Method and apparatus for protecting devices in an RF power amplifier Number:7,145,396 from the United States Patent and Trademark Office (PTO) owispatent A method and apparatus are provided for use with a power amplifier for protecting active devices on the power amplifier. A peak detector is used by control circuitry to detect the presence of a peak voltage that exceeds a threshold voltage. In response to the detection of a peak voltage, the gain of the power amplifier is reduced.<H protecting, amplifier, Method, and, appa, 7145396.html, Patent, pto, 7145396

Title: Method and apparatus for protecting devices in an RF power amplifier

Abstract: A method and apparatus are provided for use with a power amplifier for protecting active devices on the power amplifier. A peak detector is used by control circuitry to detect the presence of a peak voltage that exceeds a threshold voltage. In response to the detection of a peak voltage, the gain of the power amplifier is reduced.

Patent Number: 7,145,396 Issued on 12/05/2006 to Dupuis

Inventors: Dupuis; Timothy J. (Austin, TX)
Assignee: Silicon Laboratories, Inc. (Austin, TX)

Appl. No.: 10/673,750

Filed: September 29, 2003

Current U.S. Class: 330/298 ; 330/207P; 330/278; 330/279; 330/285

Current International Class: G06F 1/04 (20060101)

Field of Search: 330/298,207P,278,279,285

References Cited [Referenced By]

U.S. Patent Documents


3900823	August 1975	Sokal et al.
4021751	May 1977	Suzuki
4032853	June 1977	Hibbs, Jr.
4075574	February 1978	Gilbert
4122400	October 1978	Medendorp et al.
4165493	August 1979	Harrington
4590436	May 1986	Butler et al.
4604532	August 1986	Gilbert
4649467	March 1987	Vesce et al.
4772856	September 1988	Nojima et al.
4808907	February 1989	Main
4857865	August 1989	Berman et al.
4893030	January 1990	Shearer et al.
4990803	February 1991	Gilbert
5023566	June 1991	El-Hamamsy et al.
5118997	June 1992	El-Hamamsy et al.
5274341	December 1993	Sekine et al.
5291123	March 1994	Brown
5298811	March 1994	Gilbert
5327337	July 1994	Cripe
5343162	August 1994	Davis
5345185	September 1994	Gilbert
5420537	May 1995	Weedon et al.
5434537	July 1995	Kukkonen
5450036	September 1995	Nishioka et al.
5477188	December 1995	Chawla et al.
5510753	April 1996	French
5604383	February 1997	Matsuzaki
5612647	March 1997	Malec
5623231	April 1997	Mohwinkel et al.
5625205	April 1997	Kusama
5635872	June 1997	Zimmerman
5646578	July 1997	Loh et al.
5648743	July 1997	Nagaya et al.
5726603	March 1998	Chawla et al.
5742205	April 1998	Cowen et al.
5831331	November 1998	Lee
5834978	November 1998	Cho
5867061	February 1999	Rabjohn et al.
5880635	March 1999	Satoh
5942946	August 1999	Su et al.
5955926	September 1999	Uda et al.
5969582	October 1999	Boesch et al.
5973368	October 1999	Pearce et al.
5974041	October 1999	Kornfeld et al.
5986500	November 1999	Park et al.
6008698	December 1999	Dacus et al.
6011438	January 2000	Kakuta et al.
6016075	January 2000	Hamo
6047167	April 2000	Yamashita
6047168	April 2000	Carlsson
6069528	May 2000	Kashima
6133793	October 2000	Lau et al.
6137273	October 2000	Bales et al.
6147511	November 2000	Patel et al.
6157258	December 2000	Adishian et al.
6167134	December 2000	Scott et al.
6181207	January 2001	Chevallier et al.
6198347	March 2001	Sander et al.
6203516	March 2001	Kepley
6208549	March 2001	Rao et al.
6208875	March 2001	Damgaard et al.
6222788	April 2001	Forbes et al.
6232634	May 2001	Wu et al.
6265939	July 2001	Wan et al.
6274937	August 2001	Ahn et al.
6319829	November 2001	Pasco et al.
6323735	November 2001	Welland et al.
6362606	March 2002	Dupuis et al.
6384540	May 2002	Porter, Jr. et al.
6392488	May 2002	Dupuis et al.
6407639	June 2002	Jean et al.
6448847	September 2002	Paul et al.
6462620	October 2002	Dupuis et al.
6492872	December 2002	Fujioka et al.
6525611	February 2003	Dening et al.
6549071	April 2003	Paul et al.
6646511	November 2003	Canyon et al.
2002/0044018	April 2002	Dupuis et al.

Foreign Patent Documents


4419318	Jul., 1995	DE
399561	Nov., 1990	EP
0654898	May., 1995	EP
2123231	Jan., 1984	GB
03128513	May., 1991	JP
200174559	Jun., 2000	JP
WO 98/37627	Aug., 1998	WO
WO 00/16492	Mar., 2000	WO
WO 02/23716	Mar., 2002	WO

Other References

Scuderi et al. "A high performance RF power amplifier with protection againt load mismatches" IEEE Microwave Symposium Digest vol. 2, Jun. 8-13, 2003 pp. 699-702. cited by examiner .
Sokal, N. O. and Sokal, A. D., "Class E--A new class of high-efficiency tuned single ended switching power amplifiers," IEEE Journal of Solid State Circuits, vol. SC-10, No. 3, Jun. 1975, pp. 168-176. cited by other .
Makihara, Chihiro et al., "The Possibility of High Frequency Functional Ceramics Substrate", International Symposium on Mulilayer Electronic Ceramic Devices, May 5, 1998 in Cincinnati, Ohio. cited by other .
Huange et al., "A BiCMOS /Automatic Gain Control Amplifier for SONET OC-3", Proceeding of the IEEE Custom IC Conference, May 1-4, 1995, pp. 103-106. cited by other .
Webster, "Websters Ninth New Collegiate Dictionary", Merriam-Webster, 1991, p. 971. cited by other .
Toffolo et al., "Development of a CMOS switched capacitor instrumentation amplifier", IEEE Colloquium on ASICS, Apr. 10, 1992 p. 2/1. cited by othe- r .
G. Trauth V. Vanhuffel J. Trichet, "An Advanced Controller For Multi-Band Open Loop Power Control Mode RF Power Amplifier", Microwave Engineering, Jul. 2002, pp. 39-40. cited by other .
RF Micro Devices, Inc., RF3110 Triple-Band GSM/DCS/PCS Power Amp Module Data Sheet, pp. 2-401-2-412. cited by other.

Primary Examiner: Shingleton; Michael B
Attorney, Agent or Firm: Johnson & Associates

Claims

What is claimed is:

1. A circuit for protecting devices in an RF power amplifier comprising: a power detector coupled to the output of the RF power amplifier for detecting the output power of the RF power amplifier; a peak detector coupled to one or more critical nodes in the RF power amplifier for detecting peak voltages at the one or more critical nodes, wherein the peak detector further comprises a first peak detector having an input coupled to the one or more critical nodes in the RF power amplifier, and a second peak detector having an input coupled to a reference tone; a divider circuit coupled between the peak detector and the one or more critical nodes; and power control circuitry coupled to the power detector and to the peak detector for controlling the output power of the power amplifier, wherein the power control circuitry protects devices in the RF power amplifier by decreasing the gain of the power amplifier when the peak detector detects a voltage above a voltage threshold at the one or more critical nodes in the RF power amplifier.

2. The circuit of claim 1, wherein outputs of the first and second peak detectors are combined to provide a peak detection signal to the control circuitry.

3. The circuit of claim 2, wherein the first and second peak detectors are matched.

4. The circuit of claim 2, wherein the outputs of the first and second peak detectors are combined by subtracting the output of the second peak detector from the output of the first peak detector.

5. The circuit of claim 2, further comprising a divider circuit coupled between the first peak detector and the output of the power amplifier.

6. The circuit of claim 5, wherein the divider is comprised of a first and second capacitor coupled between the output of the power amplifier and ground.

7. The circuit of claim 1, further comprising a power detector coupled to the output of the power amplifier and to the control circuitry for detecting the output power of the power amplifier.

8. The circuit of claim 1, wherein the peak detector detects peak voltages present across one or more transistors in the RF power amplifier.

9. The circuit of claim 1, wherein the peak detector detects peak voltages present across one or more switching devices in the RF power amplifier.

10. The circuit of claim 1, wherein the one or more critical nodes do not include the output of the power amplifier.

11. The circuit of claim 1, wherein the divider circuit is a capacitive divider circuit.

12. The circuit of claim 1, wherein the divider circuit divides the voltage detected at the one or more critical nodes; and wherein the input of the peak detector is coupled to the divided voltage.

13. A circuit comprising: an RF power amplifier having an input and an output; a power detector coupled to the output of the RF power amplifier for detecting the output power of the RF power amplifier; a peak detector coupled to the power amplifier for detecting a peak voltage at a node of the power amplifier, wherein the node is a node other than the output of the power amplifier, wherein the peak detector is comprised of first and second matched peak detectors; and power control circuitry coupled to the peak detector and to the power amplifier for controlling the gain of the power amplifier, wherein the power control circuitry limits the power at the output of the power amplifier when the peak detector detects a peak voltage greater than a threshold voltage.

14. The circuit of claim 13, wherein the first peak detector is coupled to the output of the power amplifier and the second peak detector is coupled to a reference tone.

15. The circuit of claim 14, wherein the first and second peak detectors are matched.

16. The circuit of claim 13, further comprising a power detector coupled to the output of the power amplifier and to the power control circuitry for detecting the output power of the power amplifier.

17. The circuit of claim 13, further comprising a divider circuit coupled between the peak detector and the node of the power amplifier.

18. A circuit for protecting devices in an RF power amplifier comprising: a power detector coupled to the output of the RF power amplifier for detecting the output power of the RF power amplifier; a peak detector coupled to one or more critical nodes in the RF power amplifier for detecting peak voltages at the one or more critical nodes, wherein the peak detector further comprises a first peak detector having an input coupled to the one or more critical nodes in the RF power amplifier, and a second peak detector having an input coupled to a reference tone; and power control circuitry coupled to the power detector and to the peak detector for controlling the output power of the power amplifier, wherein the power control circuitry protects devices in the RF power amplifier by decreasing the gain of the power amplifier when the peak detector detects a voltage above a voltage threshold at the one or more critical nodes in the RF power amplifier.

19. The circuit of claim 18, wherein outputs of the first and second peak detectors are combined to provide a peak detection signal to the control circuitry.

20. The circuit of claim 19, wherein the first and second peak detectors are matched.

21. The circuit of claim 19, wherein the outputs of the first and second peak detectors are combined by subtracting the output of the second peak detector from the output of the first peak detector.

22. The circuit of claim 19, further comprising a divider circuit coupled between the first peak detector and the output of the power amplifier.

23. The circuit of claim 22, wherein the divider is comprised of a first and second capacitor coupled between the output of the power amplifier and ground.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The following U.S. patent application is expressly incorporated herein by reference: Ser. No. 09/842,456, entitled "RF POWER DETECTOR" by Timothy J. Dupuis et al, filed on Apr. 26, 2001, which is a continuation-in-part of U.S. application Ser. No. 09/660,123, filed on Sep. 12, 2000, entitled "POWER AMPLIFIER CIRCUITRY AND METHOD".

FIELD OF THE INVENTION

This invention relates to the field of power amplifiers. More particularly, this invention relates to circuitry for protecting devices in an RF power amplifier.

BACKGROUND OF THE INVENTION

In some applications utilizing a power amplifier, it is desirable to limit peak voltages to which active devices of the power amplifier are subjected. For example, in CMOS devices, the transistor breakdown voltage may be only slightly greater than the supply voltage. In RF power amplifiers, high peak voltages can be caused by load mismatches, temperature extremes, and device variations, for example. High peak voltages are capable of causing breakdown of the active devices, which can lead to reliability problems.

It can therefore be seen that there is a need for amplifier designs where peak voltages applied to active devices of the amplifier are limited so that the peak voltages are below the transistor breakdown voltages of the devices being used to implement the design.

SUMMARY OF THE INVENTION

An apparatus of the present invention provides a circuit for protecting devices in an RF power amplifier comprising: a peak detector coupled to an output of the power amplifier for detecting peak voltages at the output of the power amplifier; and control circuitry coupled to the peak detector and to the power amplifier for controlling the gain of the power amplifier, wherein the control circuitry decreases the gain of the power amplifier when the peak detector detects a voltage above a voltage threshold.

One embodiment includes a circuit comprising: an RF power amplifier having an input and an output; a peak detector coupled to the power amplifier for detecting a peak voltage at a node of the power amplifier; and power control circuitry coupled to the peak detector and to the power amplifier for controlling the gain of the power amplifier, wherein the power control circuitry limits the power at the output of the power amplifier when the peak detector detects a peak voltage greater than a threshold voltage.

Another embodiment of the invention provides a method of protecting devices in an RF power amplifier comprising the steps of: detecting a peak voltage at a first node of the power amplifier; determining whether the detected peak voltage is higher than a threshold voltage; and if it is determined that the detected peak voltage is higher than the threshold voltage, decreasing the gain of the power amplifier.

Another embodiment of the invention provides a method of controlling an RF power amplifier comprising the steps of: detecting the output power of the RF power amplifier; detecting a peak voltage at a first node of the power amplifier; increasing the gain of the power amplifier if the detected output power is less than a desired output power level and if the detected peak voltage does not exceed a threshold voltage; and decreasing the gain of the power amplifier if the detected output power is greater than the desired output power level or if the detected peak voltage exceeds a threshold voltage.

Other objects, features, and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which:

FIG. 1 is a block diagram of a protection circuit of the present invention used with a power amplifier.

FIG. 2 is a flowchart illustrating the operation of the power control circuitry shown in FIG. 1.

FIG. 3 is a block diagram of a circuit similar to the circuit shown in FIG. 1 illustrating one implementation of a peak detector.

FIGS. 4 and 5 are timing diagrams illustrating the use of the invention in applications where power is ramped.

DETAILED DESCRIPTION

In order to provide a context for understanding this description, the following illustrates an example of a typical application of the present invention. A power amplifier using the protection techniques of the present invention may be used with a wireless transmission system such as a wireless telephone or other device. In a wireless device such as a cellular telephone, the wireless device may include a transceiver, an antenna duplexer, and an antenna. Connected between the transceiver and the antenna duplexer is an RF power amplifier for amplifying signals for transmission via the antenna. This is one example of an application of a power amplifier utilizing the present invention. Of course, the invention may be used in any other application requiring a power amplifier. In the case of a wireless telephone application, the invention may be applied to GSM, CDMA, PCS, DCS, etc., or other wireless systems.

FIG. 1 is a block diagram of a protection circuit of the present invention used with a power amplifier. FIG. 1 shows a circuit 100 including a power amplifier 102 and an antenna 104 coupled to the output 106 of the power amplifier 102. A transformation network 108 is connected between the antenna 104 and the output 106 of the power amplifier 102. The input 110 of the power amplifier 102 is connected to an RF input signal RFI.

During operation, the power amplifier 102 amplifies the input signal RFI to achieve a desired output power at the antenna 104. A power detector, such as directional coupler 112, is used to detect the output power. The directional coupler 112 generates an power control signal 114 which is provided to power control circuitry 116. The power control circuitry 116 has a first input 118 for receiving an input signal relating to the requested power (i.e., the desired power level provided to the antenna 104). The desired power level may depend on various factors such that is the physical distance between a cellular phone and a base station (in a cellular phone environment). The power control circuitry 116 generates a control signal 120 which is provided to the power amplifier 102 to control the gain of the power amplifier 102.

As mentioned above, it is desirable to limit the peak voltages applied to active devices of a power amplifier resulting from a load mismatches, temperature extremes, device variations, etc. The present invention utilizes a peak detector 122 to detect the presence of peak voltages at any critical nodes of the power amplifier 102 and create a peak detection signal. An example of one suitable peak detector is described below. In the example shown in FIG. 1, the input 124 of the peak detector 122 is connected to the output 106 of the power amplifier 102. In other examples, the peak detector could be connected to other critical nodes of the power amplifier 102. In addition, the peak detector 122 (or multiple peak detectors) may be connected to multiple nodes of the power amplifier 102 to detect peak voltages at multiple nodes. The output 126 of the peak detector 122 is provided as an input to the power control circuitry 116. The power control circuitry 116 uses the output 126 from the peak detector 122 to control the power amplifier 102 in such a way that dangerous peak voltages are avoided or minimized.

FIG. 2 is a flowchart illustrating the operation of the power control circuitry shown in FIG. 1. As mentioned above, the power control circuitry 116 generates a control signal 120 based on three inputs. These inputs include the desired output power level of the power amplifier 102 (input 118), the actual detected power output level (power control signal 114), and the output of the peak detector 122 (output 126). At step 2 10, the peak voltage is detected by the peak detector 122. Next, at step 2 12, the output power is detected by the directional coupler 112. Note that the order of the steps illustrated in FIG. 2 is not essential to the invention. At step 2 14, it is determined whether the detected output power (step 2 12) is less than or equal to the requested power (as determined by the signal at input 118). If the detected output power is less than or equal to the requested power, the process proceeds to step 2 16 where it is determined whether the detected peak voltage (step 2 10) is less than the a threshold voltage (i.e., a maximum allowed voltage). The maximum allowed voltage can relate to a voltage level that does not adversely affect the active devices of the power amplifier 102, but at the same time is adequate to deliver a suitable output power level to the antenna 104. If the detected peak voltage is less than the maximum allowed voltage, the process proceeds to step 2 18 where the gain of the power amplifier 102 is increased. While FIG. 2 shows the process ending at that point, during use, the process will repeat. If, at step 2 14, it is determined that the detected output power is greater than the requested power, then the process proceeds to step 2 20 where the gain of the power amplifier 102 is decreased. Similarly, if it is determined at step 2 16 that the detected peak voltage is greater than or equal to the maximum allowed voltage, the process proceeds to step 2 20 where the gain of the power amplifier 102 is decreased.

In general, the power control circuitry 116 will adjust the gain of the power amplifier 102 until the output signal power matches the requested power. In the example described, the power control circuitry 116 increases the gain of the power amplifier 102 when the detected output power is less than the desired output power and decreases the gain when the detected output power is greater than the desired output power. However, even if the detected output power is less than the desired output power, the power control circuitry 116 will decrease the gain of the power amplifier 102 (and thereby limiting the power at the output) if the peak detector 122 has detected a peak voltage. In this way, the active devices of the power amplifier 102 are protected from high voltages, which could lead to device breakdown and overall reliability problems. The power control circuitry 116 may implement the algorithm described using analog or digital signal processing using many different techniques well known in control theory.

In some implementations, for example, if the invention is implemented using CMOS, the peak detection circuitry can be difficult to design and build with a desired accuracy. FIG. 3 is a block diagram of a circuit similar to the circuit shown in FIG. 1 illustrating one implementation of a peak detector. The circuitry illustrated in the block diagram of FIG. 3 may be used with a non-linear power amplifier and utilizes two simple peak detector circuits. FIG. 3 shows a circuit 300 which includes a power amplifier 102 and an antenna 104 coupled to the output 106 of the power amplifier 102. A transformation network 108 is connected between the antenna 104 and the output 106 of the power amplifier 102. The input 110 of the power amplifier 102 is connected to an RF input signal RFI. A directional coupler 112 generates a power control signal 114 which is provided to power control circuitry 116. The power control circuitry 116 is coupled to the power amplifier 102 and to peak detector 322.

Peak detector 322 is implemented using a first peak detector 324 and a second peak detector 326. The first peak detector 324 has an input 328 which is coupled to the output 106 of the power amplifier 102. In the example shown in FIG. 3, the input 328 is connected to a divider circuit formed by capacitors C1 and C2 connected between the power amplifier output 106 and ground. Of course, other implementations are possible. The peak detector 326 has an input 330, which is coupled to a reference tone. The reference tone may be comprised of a signal having a known amplitude at the carrier frequency. In another example, the reference tone may be comprised of a constant amplitude modulated signal (e.g., the RF input in a GSM system which has a constant amplitude and consists of GMSK modulation). The reference tone may be provided from an existing signal in the device. For example, the reference tone could come from the transmit signal of the power amplifier 102 prior to final stage amplification. In this implementation, the peak detectors 324 and 326 are matched so there are no absolute accuracy requirements on the peak detectors. The output 126 of the peak detector 322 is generated by subtracting the output of the second peak detector 326 from the output of the first peak detector 324. The output 126 provides a peak feedback signal (PFB) represented by the following the equation:

.times. ##EQU00001##

where "peak.sub.13 RFO" is the peak voltage of the output of the power amplifier 102 as detected by the first peak detector 324 and "peak_tone" is the peak voltage of the reference tone as detected by the second peak detector 326. If the peak feedback signal FBS at output 126 is positive, then the peak voltage detected by the peak detector 322 is too high. Otherwise, the peak voltage is satisfactory.

Note that the peak feedback signal at output 126 may be generated using various types of peak detectors. In one example, the peak detectors may be comprised of conventional peak detectors that simply detect the peak voltage of a signal. In another example, where the signal detected is of a known type (such as a sine wave, square wave, etc.), each peak detector may be provided by the combination of an RMS detector followed by a correction circuit. Other examples may include other types of circuits that can detect some function of the waveform that relates to the peak voltage of the waveform.

In the case where the invention is used with applications where power is ramped up from zero in a controlled manner, the invention will not allow peak voltages on the output of the power amplifier to get higher than the maximum allowed voltage. This protects the active devices in the power amplifier, while limiting the ability of the power amplifier to deliver power to the load. FIGS. 4 and 5 are timing diagrams illustrating the use of the invention in applications where power is ramped. FIG. 4 shows an example where no peak voltages are detected which exceeds the maximum allowed peak voltage. FIG. 4 shows a first plot 410 which represents the requested power signal at input 118 shown in the Figures. As shown, the plot 410 starts at zero and ramps up until it reaches a desired level (e.g., 1W). A second plot 412 is shown which represents the power measured by the directional coupler. Since no excessive peak voltages were detected in this example, the measured power ramps up and down along with the requested power signal.

FIG. 5 shows an example where a peak voltage is detected that exceeds the maximum allowed peak voltage. The arrow 508 shown in FIG. 5 illustrates the point at which a peak voltage is detected by the peak detector. When the peak voltage is detected, the power control circuitry protects the active devices in the power amplifier by reducing the gain and thus the output power of the power amplifier. In the example shown, the power measured at the output of the power amplifier (plot 512) is reduced to 0.75 Watts.

In the preceding detailed description, the invention is described with reference to specific exemplary embodiments thereof. Various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

*