Signal transmission device Number:7,394,989 from the United States Patent and Trademark Office (PTO) owispatent A transmission unit of a signal transmission device includes: a transmission-side detection unit that detects image information from an inputted electrical signal; a receiving unit that receives, from a reception unit, a status signal representing an arrival status of an outputted optical signal; and a control unit that controls an electrical-optical conversion unit on the basis of the detection result of the transmission-side detection unit and the status signal of the receiving unit so that the output of the optical signal is shut down in at least one of a case where image information is not included in an electrical signal and a case where an optical signal has not arrived.<H transmission, device, Signal, transmis, 7394989.html, Patent, pto, 7394989

Title: Signal transmission device

Abstract: A transmission unit of a signal transmission device includes: a transmission-side detection unit that detects image information from an inputted electrical signal; a receiving unit that receives, from a reception unit, a status signal representing an arrival status of an outputted optical signal; and a control unit that controls an electrical-optical conversion unit on the basis of the detection result of the transmission-side detection unit and the status signal of the receiving unit so that the output of the optical signal is shut down in at least one of a case where image information is not included in an electrical signal and a case where an optical signal has not arrived.

Patent Number: 7,394,989 Issued on 07/01/2008 to Ozeki, et al.

Inventors: Ozeki; Shinobu (Ashigarakami-gun, JP), Kobayashi; Kenichi (Ashigarakami-gun, JP), Yamada; Hidenori (Ashigarakami-gun, JP), Kyozuka; Shinya (Ashigarakami-gun, JP), Niitsu; Takehiro (Ashigarakami-gun, JP), Suzuki; Kazuhiro (Ashigarakami-gun, JP), Baba; Tomo (Ashigarakami-gun, JP), Takanashi; Osamu (Ashigarakami-gun, JP)
Assignee: Fuji Xerox Co., Ltd. (Tokyo, JP)

Appl. No.: 10/962,914

Filed: October 13, 2004

Foreign Application Priority Data


Nov 14, 2003 [JP]			2003-385961
Jul 12, 2004 [JP]			2004-204184

Current U.S. Class: 398/141 ; 398/13; 398/140; 398/15; 398/158

Current International Class: H04B 10/12 (20060101); H04B 10/00 (20060101); H04B 10/08 (20060101)

Field of Search: 398/140,141,151,158,162,136,137,138,139,9,13,15-16,25,30,33,20,135 382/100

References Cited [Referenced By]

U.S. Patent Documents


5528409	June 1996	Cucci et al.

Foreign Patent Documents


B2 2838454	Oct., 1998	JP
A 2001-185783	Jul., 2001	JP
A 2003-209920	Jul., 2003	JP

Primary Examiner: Sedighian; M. R.
Attorney, Agent or Firm: Oliff & Berridge, PLC

Claims

What is claimed is:

1. A signal transmission device comprising: a transmission unit that converts a first portion of an inputted electrical signal capable of including image information into an optical signal, converts a second portion of the electrical inputted signal into an electrical control signal including control information other than the image information, outputs the optical signal and the electrical control signal; a reception unit that inputs the optical signal and the electrical control signal, and outputs an output-use electrical signal including image information from the optical signal and a control signal; and an optical fiber cable that transmits the optical signal and an electrical cable, connecting the transmission unit and the reception unit, that transmits the electrical control signal, wherein the transmission unit includes: an electrical-optical conversion unit that converts the first portion of the inputted electrical signal into the optical signal and outputs the optical signal, a transmission-side electrical signal input and output unit that is disposed independently from the electrical-optical conversion unit and outputs the electrical control signal including control information other than the image information, a transmission-side detection unit that detects the image information from the inputted electrical signal, a receiving unit that receives, from the reception unit, a status signal representing an arrival status of the optical signal, and a control unit that controls the electrical-optical conversion unit based on a detection result of the transmission-side detection unit and the status signal of the receiving unit so that the optical signal is shut down in a case where image information is not included in the inputted electrical signal.

2. The signal transmission device of claim 1, wherein the transmission-side detection unit outputs, to the control unit, a release signal that releases a shutdown of the optical signal when the transmission-side detection unit detects image information from a no-signal state in order to output the optical signal.

3. The signal transmission device of claim 1, wherein the control unit includes a reset input unit that inputs a reset signal, the control unit controlling the electrical-optical conversion unit so that a shutdown of the optical signal is released when the reset signal has been inputted and the control unit is controlling the electrical-optical conversion unit to shut down the optical signal.

4. The signal transmission device of claim 1, wherein the control unit further includes a switch unit that supplies or cuts off power to the electrical-optical conversion unit, the control unit controlling the switch unit so that power is supplied to the electrical-optical conversion unit when a startup signal is included in the inputted electrical signal.

5. The signal transmission device of claim 4, wherein the control unit includes, in the electrical control signal, a power signal and further outputs the power signal to the reception unit when power is supplied to the electrical-optical conversion unit by the switch unit.

6. The signal transmission device of claim 5, wherein the control unit includes a power control unit that generates the electrical control signal to include the power signal and outputs the power signal to the reception unit when image information is included in the inputted electrical signal and the optical signal has arrived.

7. The signal transmission device of claim 6, wherein the power control unit generates the electrical control signal to include the power signal and outputs the power signal to the reception unit when the signal transmission device shifts from a no-signal state to a state where the image information is included in the inputted electrical signal.

8. The signal transmission device of claim 1, wherein the receiving unit sets the status signal to a voltage level for shutting down the optical signal in the control unit and outputs the status signal when the status signal is other than representing arrival of the optical signal due to at least one of non-connection and cutting.

9. The signal transmission device of claim 1, wherein the transmission-side detection unit compares an amplitude of the inputted electrical signal with a predetermined amplitude corresponding to the image information, and detects image information based on a comparison result.

10. The signal transmission device of claim 1, wherein the transmission-side detection unit includes an extraction unit that extracts a clock from the image information included in the inputted electrical signal, and the transmission-side detection unit determines that the image information is detected when the clock is extracted by the extraction unit.

11. The signal transmission device of claim 1, wherein the control unit includes a notification unit that gives notification of a fact that trouble has occurred in regard to an optical signal when the image information is detected in the transmission-side detection unit and the status signal of the receiving unit is present.

12. The signal transmission device of claim 1, wherein the electrical-optical conversion unit, the transmission-side detection unit and the control unit are configured to correspond to characteristics of image information in the inputted electrical signal.

13. A signal transmission device comprising: a transmission unit that converts a first portion of an inputted electrical signal capable of including image information into an optical signal, converts a second portion of the inputted electrical signal into an electrical control signal including control information other than the image information, outputs the optical signal and the electrical control signal; a reception unit that inputs the optical signal and the electrical control signal, and outputs an output-use electrical signal including image information from the optical signal and a control signal; and an optical fiber cable that transmits the optical signal and an electrical cable, connecting the transmission unit and the reception unit, that transmits the electrical control signal, wherein the reception unit includes: an optical-electrical conversion unit that converts the optical signal outputted from the transmission unit into an electrical signal and outputs the electrical signal, a reception-side electrical signal input and output unit that is disposed independently from the optical-electrical conversion unit and inputs and outputs the electrical control signal including control information other than the image information, and a reception-side detection unit that detects an arrival status of the optical signal from the converted electrical signal and outputs, to the transmission unit, a status signal representing the arrival status of the optical signal of the detection result, and wherein the transmission unit includes: a control unit that controls an electrical-optical conversion unit based on a detection result of a transmission-side detection unit and a status signal of a receiving unit so that the optical signal is shut down in a case where image information is not included in the inputted electrical signal.

14. The signal transmission device of claim 13, further comprising a reception-side switch unit that supplies or cuts off power to the optical-electrical conversion unit, wherein the reception-side switch unit is controlled so that power is supplied to the optical-electrical conversion unit when a signal representing that power is being supplied to the electrical-optical conversion unit by a switch unit of the transmission unit is included in the electrical control signal inputted by the reception-side electrical signal input and output unit.

15. The signal transmission device of claim 13, wherein the reception-side detection unit includes a pre-amp that amplifies a current, and the reception-side detection unit compares an amplitude of the electrical signal outputted from the pre-amp with a predetermined amplitude corresponding to a fact that the optical signal has arrived, and sets a status signal representing the arrival status of the optical signal based on a comparison result.

16. The signal transmission device of 13, wherein the optical-electrical conversion unit and the reception-side detection unit are configured to correspond to characteristics of the image information in the inputted electrical signal.

17. A signal transmission device comprising: a transmission unit that includes an electrical-optical conversion unit that converts a first portion of an inputted electrical signal into an optical signal capable of including image information and outputs the optical signal, a transmission-side electrical signal output unit that is disposed independently from the electrical-optical conversion unit and outputs an electrical control signal including control information other than the image information, a transmission-side detection unit that detects the image information from the inputted electrical signal, a receiving unit that receives, from a reception unit, a status signal representing an arrival status of the optical signal, and a control unit that controls the electrical-optical conversion unit based on a detection result of the transmission-side detection unit and the status signal of the receiving unit so that the optical signal is shut down in a case where image information is not included in the inputted electrical signal; a reception unit that includes: an optical-electrical conversion unit that converts the optical signal outputted from the transmission unit into an electrical signal and outputs the electrical signal, a reception-side electrical signal input and output unit that is disposed independently from the optical-electrical conversion unit and inputs the electrical control signal including control information other than the image information, and reception-side detection unit that detects an arrival status of the optical signal from the converted electrical signal and outputs, to the transmission unit, a status signal representing the arrival status of the optical signal of the detection result; and an optical fiber cable that transmits the optical signal and an electrical cable, connecting the transmission unit and the reception unit, that transmits the control signal.

18. A signal transmission device comprising: a transmission unit that converts a first portion of an inputted electrical signal capable of including image information into an optical signal, converts a second portion of the inputted electrical signal into an electrical control signal including control information other than the image information, outputs the optical signal and the electrical control signal; a reception unit that inputs the optical signal and the electrical control signal, and outputs an output-use electrical signal including image information from the optical signal and a control signal; and an optical fiber cable that transmits the optical signal and an electrical cable, connecting the transmission unit and the reception unit, that transmits the electrical control signal, wherein the transmission unit includes: an electrical-optical conversion unit that converts the first portion of the inputted electrical signal into the optical signal and outputs the optical signal, a transmission-side electrical signal output unit that is disposed independently from the electrical-optical conversion unit and outputs the electrical control signal including control information other than the image information, a transmission-side detection unit that detects the image information from the inputted electrical signal, a receiving unit that receives, from the reception unit, a status signal representing an arrival status of the optical signal, and a prohibition unit that generates the control signal to include a power signal and prohibits the power signal from being outputted to the reception unit based on a detection result of the transmission-side detection unit and the status signal of the receiving unit in case where image information is not included in the electrical signal.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese Patent Application Nos. 2003-385961 and 2004-204184, the disclosures of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a signal transmission device, and in particular to a signal transmission device that uses optical signals.

2. Description of the Related Art

In accompaniment with the increase in the resolution of liquid crystal panels and plasma displays, there is a demand to transmit, as digital signals, large-capacity image signals from a host. For example, in the Digital Visual Interface standard (DVI: a digital image transmission standard), which was established by the Digital Display Working Group (DDWG) that is an industry group, high-speed signals of 1.65 Gbps per 1 bit are transmitted using a differential signaling specification called transition minimized differential signaling (TMDS). A shield-attached metal cable widely used as a display cable is used as the transmission medium.

FIG. 11 shows an example where a host computer 86 and a monitor 88 are connected by a DVI cable 71 and image signals from the host computer 86 are displayed on the monitor 88. FIG. 12 shows a configural diagram of the DVI cable 71. TMDS signals in the DVI cable 71 are 4-bit differential signal pairs, and R, G and B of image signals and pixel clocks are allocated. The DVI cable 71 has a maximum transmission speed of 1.65 Gbps depending on the resolution of the image. Display data channel (DDC: display information) signals comprise (DDC Clock) and (DDC Data), and the display information (DDC) is exchanged between the host computer 86 and the monitor 88. A 5V Power signal and a hot plug detect signal (HPD: corresponding signal of the monitor) are level signals that give notification of the connection status of the host computer 86 and the monitor 88. When the host computer 86 starts up, the 5V Power signal becomes a high level, and when the 5V Power signal is inputted to the monitor 88 in a state where the host computer 86 and the monitor 88 are connected, the HPD signal becomes a high level. In addition to these, shield (GND) lines are plurally disposed in the metal DVI cable 71.

However, the length of the DVI cable 71 cannot be stretched more than 10 m because the signals that the DVI cable 71 handles are high speed. For this reason, cables (fiber cables, etc.) that convert high-speed signals to optical signals to realize long-distance transmission have also been proposed, but problems that must be resolved remain in terms of power consumption and safety in handling a laser light source for the optical signals.

For example, laser light is used in these optical transmission devices for emission light from the light source, but when there is unintentional cutting of the fiber cable or removal of the optical connector during operation, there is the potential for the laser light to leak to the outside and cause damage to human eyes. For this reason, technology that incorporates a safety circuit to stop laser light emission when the optical cable is unplugged has been proposed (e.g., see Japanese Patent Application Laid-pen Publication (JP-A) No. 2001-185783).

However, with respect to cables in which optical fiber and electrical wiring are mixed together, problems remain in that, when cutting of the light is determined only by the connection status of the electrical wiring, the cutting cannot be grasped when only the fiber cable has been cut, and the light emission cannot be appropriately stopped. Thus, it is actually preferable to monitor the reception status of the optical signal and stop light emission when normal optical signal is not being received. As a method of determining the status of transmission from the optical reception unit, technology has been proposed in the field of bi-directional optical communication that monitors the reception status of the optical signal and detects abnormalities (e.g., see Japanese Patent No. 2838454). By reflecting this technology in the aforementioned safety circuit that stops the laser light emission, it is possible to determine the connection status of the electrical wiring and the fiber cable and stop the laser light emission.

Also, as technology that achieves power saving in relation to optical extension cables, technology has been proposed that turns the power ON in accordance with the startup of the host in a state where the host and the monitor are normally connected (e.g., see JP-A No. 2003-209920). This technology proposes shutting down the power supply when the host computer and the monitor are not connected, to thereby reduce unnecessary power consumption. Thus, as long as the host computer and the monitor are normally connected, the optical transmission unit also starts up together with the startup of the host computer resulting from the power being turned ON, and the power supply of the optical transmission unit is also cut off due to the power of the host computer being cut off.

However, with respect to optical transmission devices, the function of detecting abnormalities in the optical signals and rapidly handling them and the function of achieving power saving are conflicting functions. Namely, the function of achieving power saving is technology that contradicts the safety circuit monitoring the actual optical signals. For example, sometimes the optical signal does not reach the reception circuit and, as a result, sometimes it is perceived that trouble has arisen during the time of the system startup from when the host computer is turned ON until the image signal is outputted when the initial setting of the system is being conducted (the so-called time lag), or in cases where the image signal stops when the resolution of the image is switched, or even in cases where the host computer temporarily stops the image signal within the range of normal operation.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances and provides a signal transmission device.

The present invention is applied to a signal transmission device including: a transmission unit that converts an inputted electrical signal including image information into an optical signal including the image information, converts the electrical signal into an electrical control signal including control information other than the image information, outputs the optical signal, and inputs and outputs the control signal; a reception unit that inputs the optical signal, inputs and outputs the control signal, and outputs an output-use electrical signal including image information from the optical signal and the control signal; and a transmitting unit configured by an optical fiber cable that transmits the optical signal and an electrical cable that transmits the control signal.

In this signal transmission device, an electrical signal including information outputted from a host device such as a host computer and an electrical signal (control signal) including information other than image information are inputted to the transmission unit. In the reception unit, a device represented by an image display device such as a plasma display that displays an image is connected via an electrical cable. The transmission unit and the reception unit are connected by the transmitting unit configured by an optical fiber cable that transmits the optical signal and an electrical cable that transmits the control signal. Thus, the optical signal including image information is transmitted by the optical fiber cable, and the electrical signal (control signal) including information other than the image information is transmitted by the electrical cable.

In the signal transmission device, the transmission unit of the invention includes: an electrical-optical conversion unit that converts the inputted electrical signal into an optical signal including image information and outputs the optical signal; a transmission-side electrical signal input and output unit that is disposed independently from the electrical-optical conversion unit and inputs and outputs the control signal including control information other than the image information; a transmission-side detection unit that detects the image information from the inputted electrical signal; a receiving unit that receives, from the reception unit, a status signal representing an arrival status of the outputted optical signal; and a control unit that controls the electrical-optical conversion unit on the basis of the detection result of the transmission-side detection unit and the status signal of the receiving unit so that the output of the optical signal is shut down in at least one of a case where image information is not included in the electrical signal and a case where the optical signal has not arrived.

The electrical signal including image information inputted from the host device is converted to an optical signal including the image information and outputted by the electrical-optical conversion unit. Also, the electrical signal including control information other than image information is inputted and outputted by the transmission-side electrical signal input and output unit as a control signal including the control information. Here, the transmission-side detection unit detects the image information from the electrical signal inputted from the host device. Also, in the receiving unit, the status signal representing the arrival status of the outputted optical signal is received. The control unit controls the electrical-optical conversion unit on the basis of the detection result of the transmission-side detection unit and the status signal of the receiving unit so that the output of the optical signal is shut down in at least one of a case where image information is not included in the electrical signal and a case where the optical signal has not arrived. Thus, when image information is not included in the electrical signal, the output of the optical signal can be shut down because the output of the optical signal is unnecessary, so that power can be saved. Also, when the optical signal has not arrived, such as when the optical fiber cable has been cut or unplugged, there is the potential for the optical signal, i.e., laser light to leak to the outside. Thus, by shutting this down, the safety of the laser light can be secured. Moreover, in the case of both, power saving can be realized while securing the safety of the laser light.

In the signal transmission device, a reception unit of the invention includes: an optical-electrical conversion unit that converts the optical signal outputted from the transmission unit into an electrical signal and outputs the electrical signal, a reception-side electrical signal input and output unit that is disposed independently from the optical-electrical conversion unit and inputs and outputs the control signal including control information other than the image information, and a reception-side detection unit that detects an arrival status of the optical signal from the converted electrical signal and outputs, to the transmission unit, a status signal representing the arrival status of the optical signal of the detection result.

In the reception unit of the invention, the optical signal outputted from the transmission unit is converted and outputted in the optical-electrical conversion unit. The reception-side electrical signal input and output unit disposed independently from the optical-electrical conversion unit inputs and outputs the control signal including control information other than image information outputted from the transmission unit. In this case, the reception-side detection unit detects the arrival status of the optical signal from the electrical signal converted in the optical-electrical conversion unit, includes, in the control signal, the status signal representing the arrival status of the optical signal of the detection result, and outputs this to the transmission unit. Thus, the status signal representing the arrival status of the optical signal from the reception unit can be returned from the reception unit to the transmission unit, and on the basis of this, at the transmission side, as described above, power can be saved by shutting down the output of the optical signal when image information is not included in the electrical signal, and the safety of the laser light can be secured by preventing outside leakage of the optical signal, i.e., the laser light resulting from the non-arrival of the optical signal.

According to the signal transmission device disposed with the aforementioned transmission unit and reception unit, power can be saved by shutting down the output of the optical signal, and the safety of the laser light can be secured by preventing outside leakage of the optical signal, i.e., the laser light resulting from the non-arrival of the optical signal. Specifically, the signal transmission device of the invention includes: a transmission unit that includes an electrical-optical conversion unit that converts an inputted electrical signal into an optical signal including image information and outputs the optical signal, a transmission-side electrical signal input and output unit that is disposed independently from the electrical-optical conversion unit and inputs and outputs a control signal including control information other than the image information, a transmission-side detection unit that detects the image information from the inputted electrical signal, a receiving unit that receives, from the reception unit, a status signal representing an arrival status of the outputted optical signal, and a control unit that controls the electrical-optical conversion unit on the basis of the detection result of the transmission-side detection unit and the status signal of the receiving unit so that the output of the optical signal is shut down in at least one of a case where image information is not included in the electrical signal and a case where the optical signal has not arrived; a reception unit that includes an optical-electrical conversion unit that converts the optical signal outputted from the transmission unit into an electrical signal and outputs the electrical signal, a reception-side electrical signal input and output unit that is disposed independently from the optical-electrical conversion unit and inputs and outputs the control signal including control information other than the image information, and a reception-side detection unit that detects an arrival status of the optical signal from the converted electrical signal and outputs, to the transmission unit, a status signal representing the arrival status of the optical signal of the detection result; and a transmitting unit configured by an optical fiber cable that transmits the optical signal and an electrical cable that transmits the control signal.

With respect to the transmission unit side of the signal transmission device, in consideration of the power consumption of the reception unit, power can be saved by shutting down the output of the signal representing the power supply. Specifically, a signal transmission device of the invention includes: a transmission unit that converts an inputted electrical signal including image information into an optical signal including the image information, converts the electrical signal into an electrical control signal including control information other than the image information, outputs the optical signal, and inputs and outputs the control signal; a reception unit that inputs the optical signal, inputs and outputs the control signal, and outputs an output-use electrical signal including image information from the optical signal and the control signal; and a transmitting unit configured by an optical fiber cable that transmits the optical signal and an electrical cable that transmits the control signal, wherein the transmission unit includes an electrical-optical conversion unit that converts the inputted electrical signal into an optical signal including image information and outputs the optical signal, a transmission-side electrical signal input and output unit that is disposed independently from the electrical-optical conversion unit and inputs and outputs the control signal including control information other than the image information, a transmission-side detection unit that detects the image information from the inputted electrical signal, a receiving unit that receives, from the reception unit, a status signal representing an arrival status of the outputted optical signal, and a prohibition unit that includes, in the control signal, a signal representing power supply and prohibits the signal from being outputted to the reception unit on the basis of the detection result of the transmission-side detection unit and the status signal of the receiving unit in at least one of a case where image information is not included in the electrical signal and a case where the optical signal has not arrived.

As described above, according to the present invention, the invention includes the excellent effects that power can be saved by shutting down the output of the optical signal when image information is not included in the electrical signal, the safety of the laser light can be secured by shutting down the output of the optical signal and preventing outside leakage of the laser light when the optical signal has not arrived such as when the optical fiber cable has been cut or unplugged, and either or both or these can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described in detail based on the following figures, wherein:

FIG. 1 is a diagram showing the overall configuration of an image signal transmission system pertaining to the embodiments of the invention;

FIG. 2 is a diagram showing the overall configuration of an optical transmission device pertaining to the embodiments of the invention;

FIG. 3 is a schematic configural diagram showing an electrical and optical connection relation in the optical transmission device;

FIG. 4 is a diagram showing the schematic electrical configuration of a transmission module pertaining to a first embodiment of the invention;

FIG. 5 is a diagram showing the basic conceptual configuration of an electrical-optical conversion circuit;

FIG. 6 is a diagram showing the schematic electrical configuration of a reception module;

FIG. 7 is a diagram showing the basic conceptual configuration of an optical-electrical conversion circuit;

FIG. 8 is a flow chart showing the flow of an operation in a standby state of the optical transmission device pertaining to the first embodiment of the invention;

FIG. 9 is a flow chart showing the flow of an operation in an operating state of the optical transmission device pertaining to the first embodiment of the invention;

FIG. 10 is a timing chart showing the flow of a mixed environment of the standby state and the operating state of the optical transmission device;

FIG. 11 is a schematic configural diagram showing a conventional system in which a host computer and a monitor are connected by a conventional metal DVI cable;

FIG. 12 is a schematic configural diagram showing the conventional metal DVI cable;

FIG. 13 is a characteristic diagram showing the relation between a light emission amount and an electrical current flowing in a forward direction of a diode of a semiconductor laser;

FIG. 14 is a block diagram showing the schematic electrical configuration of a transmission module pertaining to a second embodiment of the invention;

FIGS. 15A and 15B are explanatory diagrams showing a status output circuit pertaining to the second embodiment of the invention, with FIG. 15A showing main functional portions in the periphery of the status output circuit and FIG. 15B showing an operating state;

FIG. 16 is a flow chart showing the flow of an operation in a standby state of an optical transmission device pertaining to a second embodiment of the invention; and

FIG. 17 is a flow chart showing the flow of an operation in an operating state of the optical transmission device pertaining to the second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

An optical transmission device pertaining to embodiments of the invention will be described in detail below with reference to the drawings.

First Embodiment

(Overall Configuration)

As shown in FIG. 1, an image signal transmission system pertaining to the present embodiment is configured by a host computer 86, a monitor 88, an optical transmission device 10, an image signal cable 28 that is a metal DVI cable connecting the host computer 86 to the optical transmission device 10, and an image signal cable 56 that is a metal DVI cable connecting the monitor 88 to the optical transmission device 10. The optical transmission device 10 is configured by a transmission module 12, a reception module 14, and an optical fiber cable 72 and a metal cable (electrical cable) 78 that connect the transmission module 12 and the reception module 14. External power supplies 43 and 83 are connected to the transmission module 12 and the reception module 14 in order to supply power from the outside.

The optical transmission device 10 of the present embodiment corresponds to a signal transmission device of the invention, the transmission module 12 corresponds to a transmission unit of the invention, the reception module 14 corresponds to a reception unit of the invention, and the optical fiber cable 72 and the metal cable 78 correspond to an optical fiber cable and an electrical cable of the invention.

(Optical Transmission Device)

As shown in FIG. 2, the configuration of the optical transmission device 10 comprises the transmission module 12, the reception module 14, and the optical fiber cable 72 and the metal cable 78 that connect these.

(Transmission Module)

The transmission module 12 is disposed with a box-shaped housing 16 of the same shape as that of a later-described housing 46 of the reception module 14. Inside the housing 16 are disposed an electrical-optical conversion circuit board 18, which converts electrical signals to optical signals and transmits the optical signals, and an electrical signal transmission circuit board 20 that transmits inputted electrical signals. These boards are attached with screws to the housing 16. A female electrical connector 22 that inputs electrical signals is attached to one end of the electrical-optical conversion circuit board 18, and a female optical connector 24 that outputs optical signals is attached to the other end of the electrical-optical conversion circuit board 18. A laser diode 26 that outputs optical signals is internally housed in the female optical connector 24.

A male electrical connector 30 of an image signal cable 28, which is an image signal cable connected to the host computer 86, is connected to the female electrical connector 22. In the present embodiment, image signals and image control signals are outputted from a personal computer to the image signal cable 28.

Also, a female electrical connector 32 is attached to the electrical-optical conversion circuit board 18, and a male electrical connector 34 is attached to the electrical signal transmission circuit board 20. The female electrical connector 32 and the male electrical connector 34 are connected to each other. Two circuits--a power supply circuit 38 that supplies DC power to an electrical-optical conversion circuit 36 of the electrical-optical conversion circuit board 18, and an electrical signal transmission circuit 40 that transmits inputted image control signals--are disposed on the electrical signal transmission circuit board 20. Also, an external power supply 43 configured by an AC adapter 44 connected to an AC power supply is connected to the power supply circuit 38. The power supply circuit 38 controls the supply of the DC power to the electrical-optical conversion circuit 36.

The electrical signal transmission circuit board 20 is disposed with, for example, a green LED (indicated by letter "A" in the drawing) that displays the fact that the transmission module 12 is in operation. The LED (A) lights up during operation. The electrical signal transmission circuit board 20 is also disposed with, for example, a red LED (indicated by letter "B" in the drawing). The red LED (B) lights up when the transmission module 12 is not operating properly or when the signal transmission is poor. The LED (A) and the LED (B) are attached so as to be seen from the outside of the housing 16.

By poor signal transmission is meant, for example, a case where the optical fiber cable 72 is not connected or has been cut, so that the reception module 14 is unable to receive the optical signals from the optical fiber cable 72. The details will be described later.

(Reception Module)

The reception module 14 is disposed with a box-shaped housing 46 of the same shape as that of the housing 16 of the transmission module 12. Inside the housing 46 are disposed an optical-electrical conversion circuit board 48, which converts the received optical signals to electrical signals and outputs the electrical signals, and an electrical signal reception circuit board 50 that transmits inputted electrical signals. These boards are attached with screws to the housing 46. A female optical connector 51 that inputs optical signals is attached to one end of the optical-electrical conversion circuit board 48, and a female electrical connector 52 that outputs electrical signals is attached to the other end of the optical-electrical conversion circuit board 48.

A photodiode 54 that receives optical signals is internally housed in the female optical connector 51. A male electrical connector 58 of an image signal cable 56 connected to the monitor 88 (e.g., a plasma display) is connected to the female electrical connector 52. Image signals and image control signals from a later-described electrical signal reception circuit 68 are outputted from the female electrical connector 52.

Also, a female electrical connector 60 is attached to the optical-electrical conversion circuit board 48, and a male electrical connector 62 is attached to the electrical signal reception circuit board 50. The female electrical connector 60 and the male electrical connector 62 are connected to each other. A female electrical connector 70 for inputting the image control signals that the transmission module 12 has transmitted is attached to the electrical signal reception circuit board 50. Also, two circuits--a power supply circuit 66 that supplies DC power to the optical-electrical conversion circuit 64, and an electrical signal reception circuit 68 that receives the image control signals--are disposed on the electrical signal reception circuit board 50. Also, an external power supply 83 configured by an AC adapter 84 connected to an AC power supply is connected to the power supply circuit 66. The power supply circuit 66 controls the supply of the DC power to the optical-electrical conversion circuit 64.

The electrical signal reception circuit board 50 is disposed with, for example, a green LED (indicated by letter "C" in the drawing) that displays the fact that the reception module 14 is in operation. The LED (C) lights up during operation. The electrical signal reception circuit board 50 is also disposed with, for example, a red LED (indicated by letter "D" in the drawing). The red LED (D) lights up when it is detected by a diagnosis circuit that the reception module 14 is not operating properly or not receiving optical signals (when the transmission module 12 is not transmitting) or that the signal transmission is poor. The LED (C) and the LED (D) are attached so as to be seen from the outside of the housing 46. By poor signal transmission is meant, for example, a case where the optical fiber cable 72 is not connected or has been cut.

The reception module 14 includes a configuration where, in regard to the reception of the optical signals, it is determined, in accordance with the light amount of the optical signals, whether or not the optical signals from the transmission module 12 have reached the reception module 14, and which transmits an LOP signal (Loss of Power: light amount monitor signal) to the transmission module 12 via the metal cable 78.

(Electrical Connection Relation of the Optical Transmission Device)

As shown in FIG. 3, the electrical and optical connection relation of the optical transmission device 10 is configured by the transmission module 12 and the reception module 14 being connected by the optical fiber cable 72 and the metal cable 78. In the transmission module 12, TMDS signals of the image signals inputted from the host computer 86 are inputted to electrical-optical conversion circuits 36A, 36B, 36C and 36D corresponding to the individual TMDS signals. Among the individual TMDS signals, there are signals of differential signal pairs comprising data0+ and data0-, data1+ and data1-, data2+ and data2-, and Clock+ and Clock-. The individual TMDS signals are converted to optical signals in the electrical-optical conversion circuits 36A to 36D and outputted. The reception module 14 is disposed with optical-electrical conversion circuits 64A, 64B, 64C and 64D in correspondence to these differential signal pair signals. Individual optical signals are converted to corresponding TMDS signals in the optical-electrical conversion circuits 64A to 64D and outputted. The electrical-optical conversion circuit 36 comprising the electrical-optical conversion circuits 36A to 36D and the optical-electrical conversion circuit 64 comprising the optical-electrical conversion circuits 64A to 64D are connected by the optical fiber cable 72.

In the transmission module 12, signals (control signals) other than the TMDS signals of the image signals inputted from the host computer 68 are outputted to the reception module 12. Among the signals (control signals) other than the TMDS signals, there are LOP (Loss of Power: light amount monitor signal, the details of which will be described later), 5V Power, DDC Clock, DDC Data, HPD and GND signals. These signals are transmitted between the transmission module 12 and the reception module 14 connected by the metal cable 78.

In terms of the directions of the signals between the transmission module 12 and the reception module 14, the TMDS signals run in one direction from the transmission module 12 (Tx) to the reception module 14 (Rx), and as for the control signals, the Tx 5V and Clock signals run in one direction from the transmission module 12 (Tx) to the reception module 14 (Rx), the LOP and HPD signals run in one direction from the reception module 14 (Rx) to the transmission module 12 (Tx), and the Data signal runs in both directions.

Due to the above configuration, 4-bit TMDS signals are converted to optical signals by the transmission module 12 (Tx unit), which is a transceiver, and the optical signals are transmitted to the reception module 14 (Rx unit), which is a receiver, using four optical fiber cables. The reception module 14 restores the optical signals to TMDS signals and outputs the TMDS signals to the monitor 88. Here, a case is described where a fiber cable is used for each TMDS signal of the differential signal pairs, but it is also possible to reduce the number of fiber cables by multiplexing the TMDS signals using wavelength division multiplexing or time division multiplexing. A loss of power (LOP) signal that gives notification of the signal reception status of the reception module 14 is also included in these signals. In the present embodiment, the LOP signal is a high level when the reception module 14 is normally receiving the optical signals and becomes a binary level signal of a low level when the reception module 14 is not receiving the signals or when there is an abnormality in the reception.

The transmission module is disposed with a reset input end 37, for releasing the output-stop state of the optical signals, and the external power supply 43 for supplying power. Also, the reception module is disposed with the external power supply 83 for supplying power.

(Electrical Configuration of the Transmission Module)

FIG. 4 shows the schematic electrical configuration of the transmission module 12. The female electrical connector 22, which is a DVI connector of the transmission module 12, includes terminals 22A, 22B, 22C and 22D for the TMDS signals of the differential signal pairs. These terminals are connected to the electrical-optical conversion circuits 36A, 36B, 36C and 36D. The TMDS signals are converted to optical signals by the electrical-optical conversion circuit 36. Each of these electrical-optical conversion circuits 36A to 36D is connected to a power supply line 39 in order to receive the supply of power, and the power supply line 39 is connected to the external power supply 43 via an internal switch 38A internally housed in the power supply circuit 38. A terminal 22E for the 5V Power signal of the control signals other than the TMDS signals of the female electrical connector 22 is connected to the internal switch 38A. The female electrical connector 22 also includes terminals 22F, 22G, 22H and 22J for the control signals (DDC Clock, DDC Data, HPD and GND) other than the TMDS signals.

Thus, when the 5V Power signal, which is a startup signal outputted as a result of the host computer 86 starting up, is supplied (e.g., when the signal becomes a high level), the internal switch 38A becomes electrically continuous so that the external power supply 43 and the power supply line 39 are connected and the power from the external power supply 43 is supplied to the power supply line 39. When the 5V Power signal is not supplied as a result of the operation of the host computer 86 shutting down (e.g., when the signal becomes a low level), the internal switch 38A becomes electrically discontinuous so that the external power supply 38 and the power supply line 39 are not connected and the supply of power to the power supply line 39 is cut off.

Namely, the external power supply 43 is configured to supply power to the inside of the transmission module 12 via the internal switch 38A. That which controls the internal switch 38A is the 5V Power level signal that the host computer 86 outputs, so that the transmission module 12 is turned ON in association with the power of the host computer 86 being turned ON. The signal lines transmitted by the metal cable 78 may be directly connected as is, but when the cable length is long, it is preferable to insert a buffer resulting from a buffer circuit 40A. In the present embodiment, a case will be described where a buffer is inserted.

Also, the electrical-optical conversion circuits 36A to 36D are disposed with terminals that instruct input of a return to the initial state. These terminals are connected to the reset-input end 37. An instruction device such as a reset switch that outputs a reset signal as a result of being pushed is connected to the reset input end 37.

Also, the electrical-optical conversion circuits 36A to 36D are disposed with terminals that receive the input of the LOP signal from the reception module 14. These terminals are connected so that the LOP signal from the reception module 14 is inputted via a buffer 29. The buffer 29 is connected to the power supply line 39 in order to receive the supply of power.

The LOP signal is transferred by the metal cable 78, and among other signals transferred by the metal cable 78, there are the Tx 5V signal, the Clock signal, the Data signal, the HPD signal and the GND signal. The Tx 5V signal is used as a signal representing the power supply status when the power supply of the external power supply is effected by the electrical continuity of the internal switch 38A resulting from the 5V Power signal by connecting the signal terminals to the power supply line 39. It also serves as a signal representing the cutting off of the power supply from the external power supply 43 as a result of the 5V Power signal not being supplied. The Clock signal is a signal where the DDC Clock signal outputted from the terminal 22F is outputted via the corresponding buffer inside the buffer circuit 40A internally housed in the electrical signal transmission circuit 40. Similarly, the Data signal is a signal where the DDC Data signal outputted from the terminal 22G is outputted via the corresponding buffer inside the buffer circuit 40A. The HPD signal is a signal that is outputted from the reception module 14 and inputted to the terminal 22H for HPD via the corresponding buffer inside the buffer circuit 40A. The GND signal is connected as is to the metal cable 78. The buffer circuit 40A of the electrical signal transmission circuit 40 is connected to the power supply line 39 in order to receive the supply of power.

An LED (indicated by the encircled letter "A" in the drawing) is connected to the power supply line 39 and can be controlled to light up during operation.

(Electrical Configuration of the Electrical-Optical Conversion Circuit)

FIG. 5 shows the basic schematic configuration of the electrical-optical conversion circuit 36A. Here, the electrical-optical conversion circuit 36A will be representatively described, but the configurations of the other electrical-optical conversion circuits 36B to 36D are the same as that of the electrical-optical conversion circuit 36A. The electrical-optical conversion circuit 36A is disposed with a TMDS signal detector 100, a laser shutdown controller 102, a laser light amount controller 104 and a laser diode driver 106.

A laser diode 26 (26A) corresponding to the TMDS signals of the terminals 22A is connected to the output side of the laser diode driver 106. The terminals 22A for the TMDS signals are connected to a signal input side of the laser diode driver 106. The signal lines between the signal input side of the laser diode driver 106 and the terminals 22A are connected to the power supply via terminal resistors 110 and are connected to an input side of the TMDS signal detector 100. The output sides of the laser shutdown controller 102 and the laser light amount controller 104 are connected to a control signal input side of the laser diode driver 106. An output side of the TMDS signal detector 100 and output sides of the reset input end 37 and the buffer 29 that outputs the LOP signal are connected to an input side of the laser shutdown controller 102. The signal line between the input side of the laser shutdown controller 102 and the output side of the buffer 29 that outputs the LOP signal is connected via a pull-down resistor 108.

In the electrical-optical conversion circuit 36A, the laser diode driver 106 is driven by the TMDS signals, and a drive current is supplied to the laser diode 26A. The laser light amount controller 104 is for controlling the laser light amount so that the light emission amount becomes a predetermined light amount without fluctuating due to the surrounding temperature and element characteristics. Thus, the laser diode 26A lights up and off in accordance with the inputted TMDS signals. The lighting of the laser diode 26A can be forcibly stopped by the laser shutdown controller 102. Namely, the laser shutdown controller 102 can control the laser diode driver 106 so that the emission light of the laser diode 26A is forcibly stopped with a signal from the TMDS signal detector 100 or the reception status signal (LOP signal) from the reception module 14.

The operation of the laser shutdown controller 102 will be described. When, for example, the host computer 86 is outputting the TMDS signals and the LOP signal is a low level, the laser shutdown controller 102 controls the laser diode driver 106 in order to immediately stop the laser diode 26A. This is a case where, regardless of the fact that optical signals are being outputted in accordance with the output of the TMDS signals, the LOP signal is returned at a low level without the optical signals reaching the reception module 14. For this reason, in this case, it is assumed that the optical signals have not reached the reception module 14 due to some kind of trouble, and there is the potential for the laser light to be leaking to the outside of the device. Thus, the light emission of the laser diode 26A is stopped in consideration of the safety of the user.

A state where the TMDS signals are not being outputted from the host computer 86 indicates that the LOP signal is in principle a low level, i.e., that the optical signals are not reaching the reception module 14. When the output of the TMDS signals is initiated from this state, the LOP signal is returned at a low level, whereby the forced shutdown of the light emission of the laser diode 26A is maintained and the output of the TMDS signals by the optical signals cannot be done. In order to eliminate this, the LOP signal is temporarily monitored and the laser diode 26A is caused to emit light for a predetermined time necessary for the establishment of communication in a case where the state where the TMDS signals are not being outputted from the host computer 86 has shifted to the start state of the TMDS signal output when the LOP signal is a low level. Thus, output of the TMDS signals by the optical signals becomes possible.

By "predetermined time necessary for establishment of communication" is meant an amount of time equal to or greater than that sufficient for the LOP signal to be transmitted to the transmission module 12 when the laser diode 26A begins emitting light and the reception module 14 receives the optical signals and the LOP signal becomes a high level, and an amount of time equal to or less than that in which the laser light must be stopped when there is light leakage, which time is determined by laser safety standards. As a specific configuration for temporarily monitoring the LOP signal, the laser shutdown controller 102 may be disposed with a high level setter that temporarily resets the level of the LOP signal to a high level when, for example, the TMDS signals begin to be inputted, and a time-controllable delay circuit that maintains the state where the LOP signal has been temporarily reset to a high level. The delay circuit is controlled so that the laser shutdown controller 102 functions as a safety circuit during the time from when the level of the LOP signal is temporarily reset to a high level when the TMDS signals begin to be inputted to until the level of the LOP signal is again reflected after the reset, i.e., a time predetermined by experiment or calculation.

The TMDS signal detector 100 is for monitoring one of the 4-bit TMDS signals and detects whether or not a signal significant as image information is being outputted from the host computer 86. This can be realized by, for example, disposing the TMDS signal detector 100 with a peak hold circuit and comparing the voltage amplitude of the signal obtained by the peak hold circuit with a predetermined threshold. An example of the predetermined threshold is a value where the voltage amplitude in a case where a significant signal including image information is outputted from the host computer 86 is statistically predetermined by experiment or calculation.

As another example of the TMDS signal detector 100, a clock extraction function used in high-speed serial transmission can be used. Assuming that, in a case where there is a signal significant as image information, a clock of a predetermined period is embedded in the TMDS signal, the fact that a significant signal is coming when the clock component embedded in the TMDS signal can be determined and detected. Namely, this can be realized by disposing an extraction circuit that extracts the clock component from the TMDS signal and determining whether or not the signal obtained by the extraction circuit is a clock or comparing the period of the clock signal obtained by the extraction circuit with a predetermined period. An example of the predetermined threshold is a value where, in a case in which the clock period embedded in the TMDS signal is extracted when there is a signal significant as image information, a clock period of an allowed range is statistically predetermined by experiment or calculation.

With respect to the transmission line of the LOP signal, there is the potential for the level to become unstable when the metal cable 78 is not connected or is cut. In this manner, even in a case where proper notification of the LOP signal cannot be given, the level of the LOP input portion of the laser shutdown controller 102 can be forcibly established to a level where the laser diode 26A does not emit light so that the laser light is not emitted from the transmission module 12. In the present embodiment, because the LOP signal becomes a high level in an optical signal reception state, the pull-down resistor 108 is added to the inside of the transmission module 12, i.e., to the signal line between the buffer 29 and the laser shutdown controller 102. A pull-up resistor to a high level may be added in a case where the LOP signal has opposite characteristics.

An LED (indicated by the encircled letter "B" in the drawing) is connected to the laser shutdown controller 102. The laser shutdown controller 102 can control the LED so that the LED lights up when the transmission module 12 is not operating properly or when there is poor signal transmission.

(Electrical Configuration of the Reception Module)

FIG. 6 shows the schematic electrical configuration of the reception module 14. The female electrical connector 52, which is a DVI connector of the reception module 14, includes terminals 52A, 52B, 52C and 52D for the TMDS signals of the differential signal pairs. These terminals are connected to the optical-electrical conversion circuits 64A, 64B, 64C and 64D. Each of these optical-electrical conversion circuits 64A to 64D is connected to a power supply line 67 in order to receive the supply of power, and the power supply line 67 is connected to the external power supply 83 via an internal switch 66A internally housed in the power supply circuit 66. The operation of the internal switch 66A is controlled by a Tx 5V signal of the control signals other than the TMDS signals inputted via the metal cable 78.

Namely, when the Tx 5V signal is supplied (e.g., when the signal becomes a high level), the internal switch 66A becomes electrically continuous so that the external power supply 83 and the power supply line 67 are connected and the power from the external power supply 83 is supplied to the power supply line 67. When the Tx 5V signal is not supplied (e.g., when the signal becomes a low level), the internal switch 66A becomes electrically discontinuous so the supply of power to the power supply line 67 is cut off.

Namely, similar to the transmission module 12, the external power supply 83 supplies power to the reception module 14 via the internal switch 66A, but when the tran