Broadcast receiving system and method, and medium storing a broadcast reception control program Number:7,151,577 from the United States Patent and Trademark Office (PTO) owispatent For receiving a voice FM broadcast it has so far been necessary to separately provide an SAW filter and a voice intermediate frequency amplifier circuit and the freedom of circuit design has been limited.In the present invention there is used a variable filter circuit 15 (a variable filter means). The variable filter circuit 15 allows an intermediate frequency signal (IF) to pass therethrough, the intermediate frequency signal being outputted from a mixing circuit 14 as a constituent of a tuner means. The variable filter circuit 15 can change a limitation on the frequency band of the intermediate frequency signal passing therethrough. The frequency band of the intermediate frequency signal passing through the variable filter circuit 15 is thereby limited according to the type of a received broadcasting radio wave, and a VCO circuit 32 (a variable oscillator means) is controlled so as to change the oscillation frequency of an oscillation signal.<H reception, broadcast, Broadcast, recei, 7151577.html, Patent, pto, 7151577

Title: Broadcast receiving system and method, and medium storing a broadcast reception control program

Abstract: For receiving a voice FM broadcast it has so far been necessary to separately provide an SAW filter and a voice intermediate frequency amplifier circuit and the freedom of circuit design has been limited.In the present invention there is used a variable filter circuit 15 (a variable filter means). The variable filter circuit 15 allows an intermediate frequency signal (IF) to pass therethrough, the intermediate frequency signal being outputted from a mixing circuit 14 as a constituent of a tuner means. The variable filter circuit 15 can change a limitation on the frequency band of the intermediate frequency signal passing therethrough. The frequency band of the intermediate frequency signal passing through the variable filter circuit 15 is thereby limited according to the type of a received broadcasting radio wave, and a VCO circuit 32 (a variable oscillator means) is controlled so as to change the oscillation frequency of an oscillation signal.

Patent Number: 7,151,577 Issued on 12/19/2006 to Yamamoto, et al.

Inventors: Yamamoto; Kazuhiko (Daito, JP), Suzuki; Hirotsugu (Daito, JP)
Assignee: Funai Electric Co., Ltd. (Daito, JP)

Appl. No.: 10/038,725

Filed: January 8, 2002

Foreign Application Priority Data


Jan 09, 2001 [JP]			2001-000016

Current U.S. Class: 348/729 ; 348/725; 348/731; 348/733

Current International Class: H04N 5/46 (20060101)

Field of Search: 348/729,725-727,731-733,735,738,553 455/266,260,264,340,188.1

References Cited [Referenced By]

U.S. Patent Documents


4939789	July 1990	Sakashita et al.
5148280	September 1992	Wignot et al.
5293633	March 1994	Robbins
5507025	April 1996	Rodeffer
5710993	January 1998	Brekelmans
6633345	October 2003	Izuta et al.

Foreign Patent Documents


56-086538	Jul., 1981	JP
57-69356	Apr., 1982	JP
61-081034	Apr., 1986	JP
11-225295	Aug., 1999	JP

Primary Examiner: Tran; Trang U.
Attorney, Agent or Firm: Crowell & Moring LLP

Claims

We claim:

1. A broadcast receiving system comprising: a high frequency amplifier circuit which receives and amplifies a broadcasting radio wave corresponding to a desired frequency and which provides an amplified output; a local oscillator circuit which produces and outputs in a PLL circuit a local oscillation signal having a local oscillation frequency corresponding to the desired frequency of the broadcasting radio wave; a mixing circuit which mixes the output provided from the high frequency amplifier circuit with the local oscillation signal provided from the local oscillator circuit to make conversion into an intermediate frequency signal and which outputs the intermediate frequency signal; a variable filter circuit which allows the intermediate frequency signal to pass therethrough, the variable filter circuit having a band-pass filter circuit which limits the frequency band of the signal passing therethrough and a switching circuit capable of switching whether the intermediate frequency signal outputted from the mixing circuit is to pass through or bypass the band-pass filter; an SAW filter which allows the intermediate frequency signal having passed through the variable filter circuit to pass therethrough; an intermediate frequency amplifier circuit for intermediate frequency amplification of the intermediate frequency signal having passed through the SAW filter; a VCO circuit which generates an oscillation signal and which can change the oscillation frequency of the oscillation signal; a detector circuit which, on the basis of the oscillation frequency of the oscillation signal, detects the intermediate frequency signal amplified by the intermediate frequency amplifier circuit and which outputs a video signal and an audio signal; and a microcomputer which, when receiving a broadcasting radio wave in voice FM broadcast, makes control for causing the switching circuit to switch over to the side where the intermediate frequency signal is allowed to pass through the band-pass filter circuit and for causing the VCO circuit to change the oscillation frequency of the oscillation signal into an oscillation frequency corresponding to the broadcasting radio wave in the voice FM broadcast.

2. A broadcast receiving system according to claim 1, wherein: the high frequency amplifier circuit the local oscillator circuit, the mixing circuit, and the variable filter circuit are provided in a tuner IC which is connected to the microcomputer; the intermediate frequency amplifier circuit, the detector circuit, and the VCO circuit are provided in a chroma IC which is connected not only to the microcomputer but also to the tuner IC through an SAW filter; a crystal oscillator circuit which generates a reference oscillation signal of a predetermined oscillation frequency and which amplifies and outputs the reference oscillation signal through an emitter follower circuit, and a series resonance circuit connected to the crystal oscillator circuit and having a resonance frequency nearly equal to the predetermined oscillation frequency of the reference oscillation signal, are provided; the VCO circuit produces the oscillation signal in accordance with the reference oscillation signal outputted from the crystal oscillator circuit; and the local oscillator circuit acquires the reference oscillation signal through the series resonance circuit and produces the local oscillation signal in accordance with the reference oscillation signal.

3. A broadcast receiving system comprising: a tuner means which receives a broadcasting radio wave corresponding to a desired frequency and which converts it into an intermediate frequency signal and outputs the intermediate frequency signal; a variable filter means which allows the intermediate frequency signal outputted from the tuner means to pass therethrough and which can change a limitation on the frequency band of the intermediate frequency signal passing therethrough; a variable oscillator means which generates an oscillation signal and which can change the oscillation frequency of the oscillation signal; an amplifier/detector means which, in accordance with the oscillation frequency of the oscillation signal, subjects the intermediate frequency signal having passed through the variable filter means to intermediate frequency amplification and detection and which outputs a video signal and an audio signal; and a control means which, in accordance with the type of the received broadcasting radio wave, makes control to let the variable filter means limit the frequency band of the intermediate frequency signal passing therethrough and let the variable oscillator means change the oscillation frequency of the oscillation signal, wherein the variable filter means is provided with a band-pass filter circuit which limits the frequency band of a signal passing therethrough and a switching circuit capable of switching whether the intermediate frequency signal is to pass through or bypass the band-pass filter circuit; and the control means makes control to let the switching circuit switch whether the intermediate frequency signal is to pass through or bypass the band-pass filter circuit in accordance with the type of the received broadcasting radio wave.

4. A broadcast receiving system according to claim 3, wherein: when receiving a broadcasting radio wave in voice FM broadcast, the control means makes control to let the variable filter means limit the frequency band and let the variable oscillator means change the oscillation frequency of the oscillation signal into an oscillation frequency corresponding to the broadcasting radio wave in voice FM broadcast.

5. A broadcast receiving system according to claim 3, wherein: when receiving a broadcasting radio wave in voice FM broadcast, the control means makes control to let the switching circuit switch the intermediate frequency signal to the side where the signal is allowed to pass through the band-pass filter circuit.

6. A broadcast receiving system according to claim 3, wherein: the tuner means is provided with a local oscillator means which produces and outputs in a PLL circuit a local oscillation signal of a local oscillation frequency corresponding to a desired frequency of the broadcasting radio wave and is also provided with a mixing circuit which amplifies the inputted broadcasting radio wave and which mixes the thus-amplified signal with the local oscillation signal outputted from the local oscillator means to make conversion into an intermediate frequency signal, the mixing circuit then outputting the intermediate frequency signal to the variable filter means.

7. A broadcast receiving system according to claim 6, wherein: the tuner means and the variable filter means are provided in a tuner IC; the amplifier/detector means and the variable oscillator means are provided in a chroma IC which is connected to the tuner IC through an SAW filter; and the control means is provided in a microcomputer which is connected to both the tuner IC and the chroma IC.

8. A broadcast receiving system according to claim 6, wherein: a crystal oscillator circuit for generating a reference oscillation signal of a predetermined oscillation frequency is provided; the variable oscillator means produces the oscillation signal in accordance with the reference oscillation signal provided from the crystal oscillator circuit; and the local oscillator means produces the local oscillation signal in accordance with the reference oscillation signal.

9. A broadcast receiving system according to claim 8, wherein: a resonance circuit is provided which is connected to the crystal oscillator circuit and whose resonance frequency is almost equal to the predetermined oscillation frequency of the resonance oscillation signal; and the local oscillator means acquires the reference oscillation signal through the resonance circuit.

10. A broadcast receiving system according to claim 8, wherein: the crystal oscillator circuit is provided with an emitter follower circuit which amplifies the reference oscillation signal and which outputs the thus-amplified signal.

11. A broadcast receiving method comprising: receiving a broadcasting radio wave corresponding to a desired frequency and converting it into an intermediate frequency signal by means of a tuner; allowing the intermediate frequency signal to pass through a variable filter which is provided with a band-pass filter circuit which limits the frequency band of a signal passing therethrough and a switching circuit capable of switching whether the intermediate frequency signal is to pass through or bypass the band-pass filter circuit in accordance with the type of the received broadcasting radio wave; subjecting the intermediate frequency signal having passed through the variable filter to intermediate frequency amplification and simultaneous detection in accordance with an oscillation frequency provided from a variable oscillator which can change the oscillation frequency of an oscillation signal; and outputting a video signal and an audio signal, wherein according to the type of the received broadcasting radio wave there is made control to let the switching circuit switch whether the intermediate frequency signal is to pass through or bypass the band-pass filter circuit, and let the variable oscillator change the oscillation frequency of the oscillation signal.

12. A program storage device readable by a machine tangibly embodying a program of instruction executable by the machine to perform method steps for broadcast reception control, said method comprising: receiving a broadcasting radio wave corresponding to a desired frequency, converting it into an intermediate frequency signal by means of a tuner, allowing the intermediate frequency signal to pass through a variable filter which is provided with a band-pass filter circuit which limits the frequency band of a signal passing therethrough and a switching circuit capable of switching whether the intermediate frequency signal is to pass through or bypass the band-pass filter circuit, in accordance with the type of the received broadcasting radio wave; subjecting the intermediate frequency signal having passed through the variable filter to intermediate frequency amplification and simultaneous detection in accordance with an oscillation frequency provided from a variable oscillator which can change the oscillation frequency of an oscillation signal, and outputting a video signal and an audio signal, wherein according to the type of the received broadcasting radio wave there is made control to let the switching circuit switch whether the intermediate frequency signal is to pass through or bypass the band-pass filter circuit, and let the variable oscillator change the oscillation frequency of the oscillation signal.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a broadcast receiving system and method for receiving a broadcasting radio wave and producing and outputting a video signal and an audio signal, as well as a medium which stores a broadcast reception control program.

2. Description of the Prior Art

Heretofore there has been known a broadcast receiving method wherein, with use of a broadcast receiving system in television, a broadcast radio wave in voice FM broadcast is received and is converted into an intermediate frequency signal, followed by amplification and detection to produce and output an audio signal. As this type of a broadcast receiving system there is known such a system as shown in a block diagram of FIG. 8. In the same figure, the broadcast receiving system roughly comprises a tuner IC 1, an SAW filter 2, a video intermediate frequency amplifier (VIF) circuit 3 and a detector circuit 4 both incorporated in a chroma IC, a VCO circuit 5, an SAW filter 6, a voice intermediate frequency amplifier (QIF) circuit 7, and a microcomputer 8.

The tuner IC 1, which is a frequency synthesizer type tuner, receives a broadcasting radio wave in television broadcast or voice FM broadcast, then converts it into an intermediate frequency signal and outputs the same signal, under control of the microcomputer 8.

The circuit which processes the intermediate frequency signal is a split carrier type circuit. In this circuit, the intermediate frequency signal passes through the SAW filter 2 when receiving television broadcast, while it passes through the SAW filter 6 when receiving voice FM broadcast. The SAW filters 2 and 6 are for removing a disturbance component from the intermediate frequency signal. But it is necessary that the frequency band for passage of the intermediate frequency signal be made narrower when receiving voice FM broadcast than when receiving television broadcast. For this reason the passing frequency band of the SAW filter 6 is set narrower than that of the SAW filter 2.

The intermediate frequency signal which has passed through the SAW filter 2 is subjected to intermediate frequency amplification in the VIF circuit 3 and is subjected to video detection in the detector circuit 4 in accordance with an oscillation frequency of an oscillation signal inputted from the VCO circuit 5, then is converted into an RGB signal. In the course of the intermediate frequency amplification there is produced a second voice intermediate frequency signal, which in the detector circuit 4 is subjected to amplification and FM detection into an AUDIO signal. As a result, an image is projected from a picture tube in accordance with the RGB signal and voice is outputted from a speaker in accordance with the AUDIO signal.

On the other hand, the intermediate frequency signal which has passed through the SAW filter 6 is subjected to intermediate frequency amplification in the QIF circuit 7 in accordance with the oscillation frequency of the oscillation signal inputted from the VCO circuit 5 and is inputted to the detector circuit 4, in which it is subjected to amplification and FM detection into an AUDIO signal. As a result, voice is outputted from the speaker.

There also is known such a broadcast receiving system as disclosed in JP-A No. 81034/1986. In this system, both a wide band pass filer and a narrow band pass filter which permits control of a resonance frequency according to channel selection are provided in a tuner portion and are used selectively. According to the construction disclosed therein, there is detected a displacement of carrier frequency from the output of a demodulation circuit and the resonance frequency is corrected in accordance with the detected displacement. According to the JP-A No. 81034/1986, both television broadcast and voice broadcast can thereby be received by a common tuner.

However, the above conventional broadcast receiving system involves the following problems.

In the former system, for the reception of voice FM broadcast it is necessary to separately provide an SAW filter and a voice intermediate frequency amplifier circuit. Besides, since it is necessary to let the pass band of the voice FM broadcast receiving SAW filter match the oscillation frequency of the oscillation signal outputted from the VCO circuit, it is impossible to use a general-purpose SAW filter and thus the freedom of circuit design is limited.

In the latter system, both television broadcast and voice broadcast can be received by a common tuner, but it is also required to let the pass band of the voice FM broadcast receiving SAW filter match the oscillation frequency of the oscillation signal outputted from the VCO circuit.

SUMMARY OF THE INVENTION

The present invention has been accomplished in view of the above-mentioned problems and it is an object of the invention to provide a broadcast receiving system which does not require a separate provision of a filter and an intermediate frequency amplifier circuit and which can improve the freedom of circuit design.

For achieving the above-mentioned object, in a first aspect of the present invention there is provided a broadcast receiving system comprising a high frequency amplifier circuit which receives and amplifies a broadcasting radio wave corresponding to a desired frequency and which provides an amplified output, a local oscillator circuit which produces and outputs in a PLL circuit a local oscillation signal having a local oscillation frequency corresponding to the desired frequency of the broadcasting radio wave, a mixing circuit which mixes the output provided from the high frequency amplifier circuit with the local oscillation signal provided from the local oscillator circuit to make conversion into an intermediate frequency signal and which outputs the intermediate frequency signal, a variable filter circuit which allows the intermediate frequency signal to pass therethrough, the variable filter circuit having a band-pass filter circuit which limits the frequency band of the signal passing therethrough and a switching circuit capable of switching whether the intermediate frequency signal outputted from the mixing circuit is to pass through or bypass the band-pass filter, an SAW filter which allows the intermediate frequency signal having passed through the variable filter circuit to pass therethrough, an intermediate frequency amplifier circuit for intermediate frequency amplification of the intermediate frequency signal having passed through the SAW filter, a VCO circuit which generates an oscillation signal and which can change the oscillation frequency of the oscillation signal, a detector circuit which, on the basis of the oscillation frequency of the oscillation signal, detects the intermediate frequency signal amplified by the intermediate frequency amplifier circuit and which outputs a video signal and an audio signal, and a microcomputer which, when receiving a broadcasting radio wave in voice FM broadcast, makes control to let the switching circuit switch over to the side where the intermediate frequency signal is allowed to pass through the band-pass filter circuit and for causing the VCO circuit to change the oscillation frequency of the oscillation signal into an oscillation frequency corresponding to the broadcasting radio wave in the voice FM broadcast.

According this construction, the high frequency amplifier circuit receives and amplifies a broadcasting radio wave corresponding to a desired frequency and provides an amplified output. The local oscillation circuit has a PLL circuit, whereby a local oscillation signal having a local oscillation frequency corresponding to the desired frequency of the broadcasting radio wave is produced and outputted. The mixing circuit mixes the output provided from the high frequency amplifier circuit with the local oscillation signal provided from the local oscillator circuit to make conversion into an intermediate frequency signal and outputs the intermediate frequency signal to the variable filter circuit.

The variable filter circuit causes the intermediate frequency signal to pass therethrough. The variable filter circuit has a band-pass filter circuit which limits the frequency band of the signal passing therethrough, and can change the limitation on the frequency band of the intermediate frequency signal passing therethrough. Whether the frequency band of the intermediate frequency signal is to be limited or not can be decided by changing over the switching circuit.

After the intermediate frequency signal which has passed through the variable filter circuit is allowed to pass through the SAW filter, the intermediate frequency amplifier circuit amplifies the intermediate frequency signal having passed through the SAW filter.

When the VCO circuit generates an oscillation signal, the detector circuit, on the basis of the oscillation frequency of the oscillation signal, detects the intermediate frequency signal amplified in the intermediate frequency amplifier circuit and outputs a video signal and an audio signal. The VCO circuit can change the oscillation frequency of the oscillation signal which it generates.

When receiving the broadcasting radio wave in voice FM broadcast, the microcomputer makes control to let the switching circuit switch over to the side where the intermediate frequency signal is allowed to pass through the band-pass filter circuit, and at the same time makes control to let the VCO circuit change the oscillation frequency of the oscillation signal into an oscillation frequency corresponding to the broadcasting radio wave in voice FM broadcast.

As a result, at the time of receiving the broadcasting radio wave in voice FM broadcast, a disturbance component is removed from the intermediate frequency signal and there are performed intermediate frequency amplification and detection. Thus, even without separately providing an SAW filter and a voice intermediate frequency amplifier circuit, it is possible to remove the disturbance component and perform intermediate frequency amplification and detection of the converted voice intermediate frequency signal. In this case, since it is possible to change the oscillation frequency of the oscillation signal which the VCO circuit utilizes, it is not necessary to let the pass band of the intermediate frequency signal match the oscillation frequency of the oscillation signal. Consequently, it is possible to improve the freedom of circuit design.

Thus, according to the present invention it is possible to provide a broadcast receiving system capable of improving the freedom of circuit design without the need of separately providing an SAW filter and a voice intermediate frequency amplifier circuit.

The various circuits referred to above may each be constituted by a combination of such electronic components as transistor, diode, resistor, capacitor, and coil, or by an integrated circuit of those electronic components. Various configurations are available. Now, there will be given an example of acquiring a reference oscillation signal of a predetermined oscillation frequency which is for the creation of a local oscillation signal in the local oscillator circuit. That is, in a second aspect of the present invention there is provided, in combination with the above first aspect, a broadcast receiving system wherein the high frequency amplifier circuit, the local oscillator circuit, the mixing circuit and the variable filter circuit are provided in a tuner IC which is connected to the microcomputer, the intermediate frequency amplifier circuit, the detector circuit and the VCO circuit are provided in a chroma IC which is connected not only to the microcomputer but also to the tuner IC through an SAW filter, further, a crystal oscillator circuit which generates a reference oscillation signal of a predetermined oscillation frequency and which amplifies and outputs the reference oscillation signal through an emitter follower circuit, and a series resonance circuit connected to the crystal oscillator circuit and having a resonance frequency nearly equal to the predetermined oscillation frequency of the reference oscillation signal, are provided, the VCO circuit produces the oscillation signal in accordance with the reference oscillation signal outputted from the crystal oscillator circuit, and the local oscillator circuit acquires the reference oscillation signal through the series resonance circuit and produces the local oscillation signal in accordance with the reference oscillation signal.

According to this configuration, the tuner IC connected to the microcomputer is provided with a high frequency amplifier circuit, a local oscillator circuit, a mixing circuit and a variable filter circuit. The chroma IC, which is connected to the microcomputer and also connected to the tuner IC through an SAW filter, is provided with an intermediate frequency amplifier circuit, a detector circuit and a VCO circuit. Thus, with a small number of components it is possible to constitute the broadcast receiving system. It is not necessary to separately provide an SAW filter and a voice intermediate frequency amplifier circuit.

The VCO circuit generates an oscillation signal in accordance with the reference oscillation signal of a predetermined oscillation frequency generated by the crystal oscillator circuit. The local oscillator circuit also generates a local oscillation signal in accordance with the reference oscillation signal generated by the crystal oscillator circuit. That is, it is no longer required to use a crystal oscillator circuit exclusive for the local oscillator circuit and hence it becomes possible to reduce the number of crystal oscillator used.

Since the series resonance circuit connected to the crystal oscillator circuit resonates the reference oscillation signal at a resonance frequency of the reference oscillation frequency, attenuation of the reference oscillation signal is prevented. Thus, the local oscillator circuit can acquire an unattenuated reference oscillation signal. The reference oscillation signal is amplified by the emitter follower circuit and there is provided an output of low impedance, whereby the influence of a mixed electrical noise can be diminished. Therefore, even when the distance from the crystal oscillator circuit is long and so is a signal line of the reference oscillation signal, the local oscillator circuit can utilize the reference oscillation signal provided from the crystal oscillator circuit.

Thus, in this configuration it becomes unnecessary to use a crystal oscillator circuit exclusive for the local oscillator circuit and hence becomes possible to reduce the number of crystal oscillator used. In this connection, even if the distance from the crystal oscillator circuit is long and so is a signal line of the reference oscillation signal, it is possible for the local oscillator circuit to utilize the reference oscillation signal provided from the crystal oscillator circuit.

The present invention is also applicable to other configurations than the above circuit configurations. More particularly, in a third aspect of the present invention there is provided a broadcast receiving system comprising a tuner means which receives a broadcasting radio wave corresponding to a desired frequency and which converts it into an intermediate frequency signal and outputs the intermediate frequency signal, a variable filter means which allows the intermediate frequency signal outputted from the tuner means to pass therethrough and which can change a limitation on the frequency band of the intermediate frequency signal passing therethrough, a variable oscillator means which generates an oscillation signal and which can change the oscillation frequency of the oscillation signal, an amplifier/detector means which, in accordance with the oscillation frequency of the oscillation signal, subjects the intermediate frequency signal having passed through the variable filter means to intermediate frequency amplification and detection and which outputs a video signal and an audio signal, and a control means which, in accordance with the type of the received broadcasting radio wave, makes control to let the variable filter means limit the frequency band of the intermediate frequency signal passing therethrough and let the variable oscillator means change the oscillation frequency of the oscillation signal.

According to this configuration, when the tuner means receives the broadcasting radio wave corresponding to the desired frequency, then converts it into an intermediate frequency signal and outputs the intermediate frequency signal, the variable filter means allows the intermediate frequency signal to pass therethrough. At this time, it is possible to change the limitation on the frequency band of the passing intermediate frequency signal.

When the variable oscillator means generates an oscillation signal, the amplifier/detector means subjects the intermediate frequency signal having passed through the variable filter to intermediate frequency amplification and detection in accordance with the oscillation frequency of the oscillation signal and outputs a video signal and an audio signal. The variable oscillator means can change the oscillation frequency of the oscillation signal which is generated.

In accordance with the type of the received broadcasting radio wave the control means makes control to let the variable filter means limit the frequency band of the intermediate frequency signal passing therethrough and at the same time makes control to let the variable oscillator means change the oscillation frequency of the oscillation signal.

Therefore, in the case of receiving a broadcasting radio wave for which it is necessary to limit the frequency band of the intermediate frequency signal, if the intermediate frequency signal is limited by the variable filter means to the frequency band matching the type of the broadcasting radio wave and the oscillation frequency of the oscillation signal is changed by the variable oscillator means and further if the intermediate frequency signal having passed through the variable filter means is amplified by the amplifier/detector means, a disturbance component is removed from the intermediate frequency signal and there are performed intermediate frequency amplification and detection. That is, even without separate provision of a filter and an intermediate frequency amplifier circuit, the converted intermediate frequency signal after the removal of a disturbance component can be subjected to intermediate frequency amplification and detection. At this time, since it is possible to change the oscillation frequency of the oscillation signal which the amplifier/detector means utilizes, it is not necessary to let the pass band of the intermediate frequency signal match the oscillation frequency of the oscillation signal. Consequently, it is possible to improve the freedom of circuit design.

Thus, it is possible to provide a broadcast receiving system which does not require separate provision of a filter and an intermediate frequency amplifier circuit and which permits improving the freedom of circuit design.

As an example of the above control, in a fourth aspect of the present invention there is provided, in combination with the above third aspect, a broadcast receiving system wherein when receiving a broadcasting radio wave in voice FM broadcast, the control means makes control to let the variable filter means limit the frequency band and let the variable oscillator means change the oscillation frequency of the oscillation signal into an oscillation frequency corresponding to the broadcasting radio wave in voice FM broadcast.

According to this configuration, when receiving the broadcasting radio wave in voice FM broadcast, the frequency band of the intermediate frequency signal passing through the variable filter means is limited and the oscillation frequency of the oscillation signal changes to an oscillation frequency corresponding to the broadcasting radio wave in voice FM broadcast. That is, an example of the control means can be provided. This example is suitable for receiving the broadcasting radio wave in voice FM broadcast by utilizing the broadcast receiving system in television.

Of course, various types of broadcasting radio waves are conceivable wherein the frequency band of an intermediate frequency signal is limited. For example, the present invention may be applied to receiving a broadcasting radio wave in voice AM broadcast.

By so doing, it is possible to provide an example of the control means.

The variable filter means which allows the intermediate frequency signal outputted from the tuner means to pass therethrough may be configured variously insofar as it can change the limitation on the frequency band of the passing intermediate frequency signal. As an example thereof, in a fifth aspect of the present invention there is provided, in combination with the above third aspect, a broadcast receiving system wherein the variable filter means is provided with a band-pass filter circuit which limits the frequency band of a signal passing therethrough and a switching circuit capable of switching whether the intermediate frequency signal is to pass through or bypass the band-pass filter circuit, and the control means makes control to let the switching circuit switch whether the intermediate frequency signal is to pass through or bypass the band-pass filter circuit, in accordance with the type of the received broadcasting radio wave.

According to this configuration, by making control to switch the switching circuit, it becomes possible for the control means to make control whether the frequency band of the intermediate frequency signal is to be limited or not. That is, the variable filter means is constituted by both the band-pass filter circuit and the switching circuit.

In this way the variable filter means can be fabricated from both the band-pass filter circuit and the switching circuit.

As an example of configuration wherein a broadcasting radio wave in voice FM broadcast is received by utilizing the variable filter means described above, in a sixth aspect of the present invention there is provided, in combination with the above fifth aspect, a broadcast receiving system wherein, when receiving a broadcasting radio wave in voice FM broadcast, the control means makes control to let the switching circuit switch the intermediate frequency signal to the side where the signal is allowed to pass through the band-pass filter circuit.

According to this configuration, when receiving the broadcasting radio wave in voice FM broadcast, the intermediate frequency signal passes through the band-pass filter circuit, so that the frequency band of the intermediate frequency signal can be limited. That is, it is possible to provide an example of controlling the switching operation of the switching circuit.

The tuner means may be configured variously insofar as it can receive a broadcasting radio wave corresponding to a desired frequency and is capable of converting it into an intermediate frequency signal and outputting it. As an example thereof, in a seventh aspect of the present invention there is provided, in combination with the above third aspect, a broadcast receiving system wherein the tuner means is provided with a local oscillator means which produces and outputs in a PLL circuit a local oscillation signal of a local oscillation frequency corresponding to a desired frequency of the broadcasting radio wave and is also provided with a mixing circuit which amplifies the inputted broadcasting radio wave and which mixes the thus-amplified signal with the local oscillation signal outputted from the local oscillator means to make conversion into an intermediate frequency signal, the mixing circuit then outputting the intermediate frequency signal to the variable filter means.

According to this configuration, the local oscillation means has a PLL circuit, whereby a local oscillation signal of a local oscillation frequency corresponding to the desired frequency of the received broadcasting radio wave is produced and outputted. The mixing means amplifies the inputted broadcasting radio wave, mixes the amplified signal with the local oscillation signal outputted from the local oscillator means to make conversion into an intermediate frequency signal and then outputs the intermediate frequency signal to the variable filter means. That is, the tuner means is constituted by both the local oscillator means and the mixing means.

The frequency of the converted intermediate frequency signal is the difference or sum between the local oscillation frequency and the frequency of the signal amplified from the broadcasting radio wave. Therefore, by controlling the local oscillation frequency of the local oscillation signal it is possible to determine the frequency of the intermediate frequency signal.

The various means described above may be constituted by a combined circuit of electronic components including transistor or by utilizing an integrated circuit of those electronic components. Various configurations are available. As an example thereof, in an eighth aspect of the present invention there is provided, in combination with the above seventh aspect, a broadcast receiving system wherein the tuner means and the variable filter means are provided in a tuner IC, the amplifier/detector means and the variable oscillator means are provided in a chroma IC which is connected to the tuner IC through an SAW filter, and the control means is provided in a microcomputer which is connected to both the tuner IC and the chroma IC.

According to this configuration, the tuner IC is provided with the tuner means and the variable filter means, the chroma IC connected to the tuner IC through an SAW filter is provided with the amplifier/detector means and the variable oscillator means, and the microcomputer connected to both the tuner IC and the chroma IC is provided with the control means. That is, the broadcast receiving system in question can be constituted with use of a reduced number of components. In this case, it is not necessary to separately provide a filter and an intermediate frequency amplifier circuit.

As an example of acquiring a reference oscillation signal of a predetermined oscillation frequency which is used for the local oscillator means to produce a local oscillation signal, in a ninth aspect of the present invention there is provided, in combination with the above seventh aspect, a broadcast receiving system wherein there is provided a crystal oscillator circuit for generating a reference oscillation signal of a predetermined oscillation frequency, the variable oscillator means produces the oscillation signal in accordance with the reference oscillation signal provided from the crystal oscillator circuit, and the local oscillator means produces the local oscillation signal in accordance with the reference oscillation signal.

According to this configuration, the variable oscillator means produces an oscillation signal in accordance with the reference oscillation signal of the predetermined oscillation frequency provided from the crystal oscillator circuit. Also as to the local oscillator means, it produces a local oscillation signal in accordance with the reference oscillation signal provided from the crystal oscillator circuit. That is, it is not necessary to use a crystal oscillator circuit exclusive for the local oscillator means and hence it is possible to reduce the number of crystal oscillator used. Even when the oscillation frequency of the reference oscillation signal which the local oscillator means utilizes changes, this can be coped with by a corrective calculation which is performed by the control means.

Of course, the configuration wherein the local oscillator means also utilizes the reference oscillation signal which the variable oscillator means utilizes, is a mere example. If there is provided a crystal oscillator circuit not connected to the variable oscillator means, there may be utilized a reference oscillation signal produced by the crystal oscillator circuit. It is also possible to utilize a reference oscillation signal generated by a crystal oscillator circuit which is exclusive for the local oscillator means, because the resulting demerit is a mere incapability of reducing the number of crystal oscillator. The local oscillator means can acquire reference oscillation signals from various crystal oscillator circuits.

As an example of the configuration wherein the local oscillator means acquires a reference oscillation signal, in a tenth aspect of the present invention there is provided, in combination with the above ninth aspect, a broadcast receiving system wherein there is provided a resonance circuit which is connected to the crystal oscillator circuit and whose resonance frequency is almost equal to the predetermined oscillation frequency of the reference oscillation signal, and the local oscillator means acquires the reference oscillation signal through the resonance circuit.

According to this configuration, it is possible to prevent attenuation of the reference oscillation signal because the resonance circuit connected to the crystal oscillator circuit resonates the reference oscillation signal with a resonance frequency of the reference oscillation frequency. Consequently, the local oscillator means can acquire a reference oscillation signal which is not attenuated. Accordingly, even when the distance from the crystal oscillator circuit is long and so is a signal line of the reference oscillation signal, the local oscillator means can utilize the reference oscillation signal provided from the crystal oscillator circuit.

Various configurations are available for the resonance circuit insofar as the resonance frequency is almost equal to the predetermined oscillation frequency of the reference oscillation signal. For example, it is possible to utilize a series resonance circuit of coil and capacitor.

As an example of the configuration wherein the crystal oscillator circuit outputs the reference oscillation signal, in an eleventh aspect of the present invention there is provided, in combination with the above ninth aspect, a broadcast receiving system wherein the crystal oscillator circuit is provided with an emitter follower circuit which amplifies the reference oscillation signal and which outputs the thus-amplified signal.

According to this configuration, the reference oscillation signal is amplified by the emitted follower circuit. At this time, the output of the reference oscillation signal becomes low in impedance, so that it is possible to diminish a mixed electrical noise, and even if a signal line of the reference oscillation signal is long, the local oscillator means can utilize the reference oscillation signal provided from the crystal oscillator circuit.

Of course, the above technique is not limited to its application to a substantial system, but is also effective as a method thereof. In a twelfth aspect of the present invention there is provided a broadcast receiving method comprising receiving a broadcasting radio wave corresponding to a desired frequency and converting it into an intermediate frequency signal by means of a tuner, allowing the intermediate frequency signal to pass through a variable filter which can change a limitation on the frequency band of the signal passing therethrough, subjecting the intermediate frequency signal having passed through the variable filter to intermediate frequency amplification and simultaneous detection in accordance with an oscillation frequency provided from a variable oscillator which can change the oscillation frequency of an oscillation signal, and outputting a video signal and an audio signal, wherein according to the type of the received broadcasting radio wave there is made control to limit the frequency band of the intermediate frequency signal passing through the variable filter and let the variable oscillator change the oscillation frequency of the oscillation signal.

The concept of the invention is not limited to the above, but includes various modes. In some case such a broadcast receiving system exists alone or in another case it is utilized in an incorporated state into a certain apparatus. Thus, a change may be made appropriately between software and hardware.

In the case where an embodied example of the invention concept is software, it is inevitably considered that the invention concept exists and is utilized also on a recording medium which stores the software.

Therefore, in a thirteenth aspect of the present invention there is provided a medium storing a broadcast reception control program, the broadcast reception control program being used in receiving a broadcasting radio wave corresponding to a desired frequency, converting it into an intermediate frequency signal by means of a tuner, allowing the intermediate frequency signal to pass through a variable filter which can change a limitation on the frequency band of the signal passing therethrough, subjecting the intermediate frequency signal having passed through the variable filter to intermediate frequency amplification and simultaneous detection in accordance with an oscillation frequency provided from a variable oscillator which can change the oscillation frequency of an oscillation signal, and outputting a video signal and an audio signal, wherein a computer is allowed to implement a function of making control to let the variable filter limit the frequency band of the intermediate frequency signal passing therethrough and let the variable oscillator change the oscillation frequency of the oscillation signal.

Of course, the above storage medium may be a magnetic storage medium or a magneto-optic storage medium. Just the same thinking is also applicable to all of storage mediums to be developed in future. This is completely true of duplicating stages, including primary and secondary duplicate products.

The concept of the invention is further applicable in just the same manner to the case where the invention is implemented partially by software and partially by hardware. The invention may be implemented in a mode such that the program is partially stored on the storage medium and is read as necessary. It goes without saying that the invention concept is reflected rather in the program itself.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing schematically the configuration of a combined voice FM broadcast receiver and television to which is applied a broadcast receiving system according to an embodiment of the present invention;

FIG. 2 is a block diagram showing the configuration of the broadcast receiving system;

FIG. 3 is a block diagram showing the configuration of a local oscillator circuit;

FIG. 4 is a block diagram showing the configuration of a variable filter circuit;

FIG. 5 is a circuit diagram showing schematically a crystal oscillator circuit and a series resonance circuit;

FIG. 6 is a flowchart showing schematically a control processing carried out by a microcomputer;

FIG. 7 is a flowchart showing an example of a control processing carried out by the microcomputer; and

FIG. 8 is a block diagram showing schematically the configuration of a conventional broadcast receiving system.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention will be described hereinunder with reference to the drawings.

FIG. 1 illustrates in terms of a block diagram a schematic configuration of a combined voice FM broadcast receiver and television to which is applied a broadcast receiving system 100 according to an embodiment of the present invention. An operation panel and a remote controller to be used by a user are not shown in the same figure.

In FIG. 1, the broadcast receiving system 100 is roughly composed of a tuner IC 10, a SAW (Surface Acoustic Wave) filter 20 connected to the tuner IC 10, a chroma IC 30 connected to the SAW filter 20, a crystal oscillator circuit 40 connected to the chroma IC 30, a series resonance circuit 50 connected to both crystal oscillator circuit 40 and tuner IC 10, and a microcomputer 60 connected to both tuner IC 10 and chroma IC 30. The tuner IC 10, chroma IC 30 and microcomputer 60 are connected to an IIC bus 70. The microcomputer 60 controls the entire television by serial data communication, thereby implementing the function as a combined voice FM broadcast receiver and television.

FIG. 2 is a block diagram showing the configuration of the broadcast receiving system 100, in which the IIC bus 70 is not shown.

The tuner IC 10, which is a frequency synthesizer type tuner, receives a radio wave in television broadcast or voice FM broadcast, then converts it into an intermediate frequency signal and outputs the intermediate frequency signal, under control of the microcomputer 60.

In FIG. 2, the tuner IC 10 is provided with a high frequency amplifier circuit 12 connected to both antenna 11 and microcomputer 60, a local oscillator circuit 13 connected to both series resonance circuit 50 and microcomputer 60, a mixing circuit 14 connected to both local oscillator circuit 13 and high frequency amplifier circuit 12, and a variable filter circuit 15 connected to all of mixing circuit 14, SAW filter 20 and microcomputer 60. The variable filter circuit 15 has a band-pass filter circuit 16 and a switching circuit 17, the switching circuit 17 being connected to the microcomputer 60 located outside.

The high frequency amplifier circuit 12, local oscillator circuit 13 and mixing circuit 14 may be any of various circuits for television which have been adopted heretofore.

The high frequency amplifier circuit 12 has a band30 pass filter (not shown) and, under control of the microcomputer 60, receives a broadcasting radio wave corresponding to a desired frequency from the antenna 11 through the band-pass filter and amplifies it into a high frequency signal. The frequency of this high frequency signal is the same as that of the broadcasting radio wave in a selected channel. The high frequency amplifier circuit outputs the high frequency signal to the mixing circuit 14.

As shown in FIG. 3, the local oscillator circuit 13 is constituted by a PLL (Phase Locked Loop) circuit. With the PLL circuit, a local oscillation signal of a local oscillation frequency corresponding to the desired frequency of the broadcasting radio wave is produced and outputted to the mixing circuit 14. That is, the local oscillator circuit 13 constitutes the local oscillator means as referred to herein. In the figure, the series resonance circuit 50 and the microcomputer 60 are indicated by dotted lines.

In FIG. 3, a local oscillation signal outputted from a voltage-controlled oscillator 13a is inputted to a pre-frequency divider 13b which is set to a predetermined frequency dividing ratio, and is frequency-divided, then is further inputted to a variable frequency divider 13c and is frequency-divided. The microcomputer 60 controls the frequency dividing ratio of the variable frequency divider 13c so as to give a local oscillation frequency corresponding to the desired frequency which is received. On the other hand, a reference oscillation signal is fed from the series resonance circuit 50 to a frequency divider 13d which is set to a predetermined frequency dividing ratio, and is frequency-divided. The thus frequency-divided local oscillation signal and reference oscillation signal are inputted to a phase detector 13e, from which a detection output as a result of frequency comparison is fed to an integrating circuit 13f. From the integrating circuit 13f is provided a voltage output which varies depending on the detection output. This voltage output is fed to the voltage-controlled oscillator 13a and the frequency of the local oscillation signal is made coincident with the local oscillation frequency corresponding to the desired frequency.

The local oscillation frequency differs according to countries. For example, in the case of receiving television broadcast in the U.S., a local oscillation frequency is set 45.75 MHz higher than the frequency of the high frequency signal outputted from the high frequency amplifier circuit 12. In the case of receiving television broadcast in Japan, a local oscillation frequency is 58.75 MHz higher than the frequency of the high frequency signal.

The mixing circuit 14 mixes the output from the high frequency amplifier circuit 12 with the local oscillation signal provided from the local oscillator circuit 13 to make conversion into an intermediate frequency signal and outputs the intermediate frequency signal to the variable filter circuit 15. That is, the high frequency amplifier circuit 12 and the mixing circuit 14 constitute the mixing means as referred to in the present invention.

The frequency of the intermediate frequency signal corresponds to the local oscillation frequency of the local oscillation signal minus the frequency of the high frequency signal. For example, in the case of setting for reception of television broadcast in the U.S., the frequency of the intermediate frequency signal is 45.75 MHz. In the U.S. television broadcast, the frequency of a voice component in the intermediate frequency signal is set at 41.25 MHz.

Thus, the high frequency amplifier circuit 12, local oscillator circuit 13 and mixing circuit 14, which receive a broadcasting radio wave corresponding to a desired frequency, make conversion into an intermediate frequency signal and output the intermediate frequency signal, constitute the tuner means as referred to in the present invention.

As shown in FIG. 4, the variable filter circuit 15 has a band-pass filter 16a which constitutes the band-pass filter circuit 16 and a switch 17a which constitutes the switching circuit 17, and allows the intermediate frequency signal outputted from the mixing circuit 14 to pass therethrough. In the same figure, the mixing circuit 14, SAW filter 20 and microcomputer 60 are indicated by dotted lines.

In FIG. 4, the band-pass filter 16a is of a narrow band and limits the frequency band of the intermediate frequency signal passing therethrough. For example, in the case where the band-pass filter 16a has a frequency passing characteristic of 42.0.+-.1.0 MHz, a component smaller than 41.0 MHz and a component larger than 43.0 MHz in the intermediate frequency signal passing through the band-pass filter 16a are cut off. The frequency band limited by the band-pass filter 16a is included in the frequency band limited by the SAW filter 20.

If the switch 17a is not incorporated into the tuner IC 10, it can be constituted, for example, by combination with a switching transistor. In accordance with a signal of high or low voltage level outputted from the microcomputer 60 the switch 17a can switch whether the intermediate frequency signal outputted from the mixing circuit 14 is to pass through or bypass the band-pass filter 16a.

The variable filter circuit 15 which can thus allow the intermediate frequency signal provided from the mixing circuit 14 to pass therethrough and which can change the limitation on the frequency band of the intermediate frequency signal passing therethrough, constitutes the variable filter means as referred to in the present invention.

The SAW filter 20 is a band-pass filter of a wide band which allows the intermediate frequency signal having passed through the variable filter circuit 15 to pass therethrough. The SAW filter 20 has a comb-shaped electrode formed on a piezoelectric substrate, whereby when the intermediate frequency signal moves through the comb-shaped electrode, the component outside the predetermined frequency band is eliminated. Consequently, as the intermediate frequency signal passes through the SAW filter 20, a disturbance component outside the predetermined frequency band is eliminated.

Of course, instead of the SAW filter 20 there may be used any of various band-pass filter circuits so far adopted as circuits for television.

The chroma IC 30 is provided with an intermediate frequency amplifier (VIF) circuit 31 connected to the SAW filter 20, a VCO (Voltage Controlled Oscillator) circuit 32 connected to both crystal oscillator circuit 40 and microcomputer 60, a detector circuit 33 connected to both VCO circuit 32 and VIF circuit 31, and a synchronizing circuit 34 connected to the detector circuit 33. It suffices for the broadcast receiving system 100 according to the present invention to permit the generation of both video (RGB) signal and audio (AUDIO) signal from the inputted broadcasting radio wave, but in this embodiment the synchronizing circuit 34 is also provided in the chroma IC 30 for the purpose of reducing the number of components used as a whole of television.

As the VIF circuit 31, VCO circuit 32, detector circuit 33 and synchronizing circuit 34 there may be used any of various conventional circuits for television.

The VIF circuit 31 subjects the intermediate frequency signal having passed through the SAW filter 20 to intermediate frequency amplification. The thus-amplified intermediate frequency signal is then inputted to the detector circuit 33.

The VCO circuit 32 can change the oscillation frequency of an oscillation signal which is generated in accordance with an inputted voltage. The VCO circuit 32 generates an oscillation signal at an oscillation frequency corresponding to the voltage. The microcomputer 60 controls the voltage inputted to the VCO circuit 32 so as to give an oscillation frequency corresponding to the type of the received broadcasting radio wave. That is, the oscillation frequency of the oscillation signal is changed in accordance with the type of the received broadcasting radio wave.

For example, in the case of receiving television broadcast in the U.S., the oscillation frequency of an oscillation signal is set at 45.75 MHz which is equal to the foregoing difference between the local oscillation frequency and the frequency of a high frequency signal. In the case of receiving voice FM broadcast in the U.S., the oscillation frequency of an oscillation signal is determined to be a frequency which is 4.5 MHz larger than the frequency of the intermediate frequency signal produced in the mixing circuit 14. As an example, when the frequency of the intermediate frequency signal is 42.0 MHZ, the oscillation frequency of the oscillation signal is 42.0+4.5=46.5 MHz.

The VCO circuit 32 which thus generates an oscillation signal and which can change the oscillation frequency of the oscillation signal, constitutes the variable oscillator means as referred to in the present invention.

In accordance with the oscillation frequency of the oscillation signal the detector circuit 33 detects the intermediate frequency signal amplified in the VIF circuit 31 and outputs both RGB signal and an AUDIO signal. More specifically, the detector circuit 33 performs video detection from the amplified intermediate frequency signal while synchronizing to the oscillation frequency of the oscillation signal, separates RGB signal by performing a predetermined color demodulation and outputs it to the exterior. As to the audio signal, the detector circuit 33 mixes a voice