Power amplifier self-heating compensation circuit
Temperature compensation circuits and methods for adjusting one or more circuit parameters of a power amplifier (PA) to maintain approximately constant Gain versus time during pulsed operation sufficient to substantially offset self-heating of the PA. Some embodiments compensate for PA Gain “droop” due to self-heating using a Sample and Hold (S&H) circuit. The S&H circuit samples and holds an initial temperature of the PA at commencement of a pulse. Thereafter, the S&H circuit generates a continuous measurement that corresponds to the temperature of the PA during the remainder of the pulse. A Gain Control signal is generated that is a function of the difference between the initial temperature and the operating temperature of the PA as the PA self-heats for the duration of the pulse. The Gain Control signal is applied to one or more adjustable or tunable circuits within a PA to offset the Gain droop of the PA.
1. A compensation circuit configured to monitor a target circuit having one or more performance parameters affected by heating during operation of the target circuit, the compensation circuit including:
(a) at least one sensor located with respect to the target circuit so as to measure the temperature of the target circuit and generate an output signal T representing such temperature;
(b) at least one sample and hold circuit, each coupled to at least one sensor through an intermediate amplifier coupled between the at least one sensor and the at least one sample and hold circuit, configured to capture a temperature T(t=t 0 ) at a time to after commencement of operation of the target circuit, and to sample a temperature T(t>t 0 ) at times after time t 0 ;
(c) a comparison circuit, coupled to at least one sample and hold circuit, for determining a signal ΔT=T(t>t 0 )−T(t=t 0 ); and
(d) a mapping circuit, coupled to the comparison circuit, for receiving values of the signal ΔT and mapping the values of the signal ΔT to corresponding control signal values, the compensation circuit being configured to couple the control signal values to circuitry controlling the one or more performance parameters of the target circuit.
2. A time division duplexing radio system including (1) a power amplifier having a Gain that droops due to heating of the power amplifier during pulsed operation, and (2) a temperature compensation circuit, the temperature compensation circuit including:
(a) at least one sensor located with respect to the power amplifier so as to measure the temperature of the power amplifier and generate an output signal T representing such temperature;
(b) at least one sample and hold circuit, each coupled to at least one sensor through an intermediate amplifier coupled between the at least one sensor and the at least one sample and hold circuit, configured to capture a temperature T(t=t 0 ) at a time t 0 after commencement of pulsed operation of the power amplifier, and to sample a temperature T(t>t 0 ) at times after time t 0 ;
(c) a comparison circuit, coupled to at least one sample and hold circuit, for determining a signal ΔT=T(t>t 0 )−T(t=t 0 ); and
(d) a mapping circuit, coupled to the comparison circuit, for receiving values of the signal ΔT and mapping the values of the signal ΔT to corresponding control signal values, the control signal values being coupled to one or more adjustable circuits to adjust one or more circuit parameters of the one or more adjustable circuits.
3. The invention of claim 2 , wherein the time division duplexing radio system is a WiFi system.
4. The invention of claim 3 , wherein each pulse of pulsed operation of the power amplifier corresponds to a WiFi long packet.
5. The invention of claim 2 , wherein the control signal values maintain the Gain of the power amplifier within about ±0.05 dB during at least a 4 mS operational pulse of the power amplifier.
6. The invention of claim 2 , wherein the temperature T(t=t 0 ) is captured within about 10 μS after commencement of an operational pulse of the power amplifier.
7. The invention of claim 2 , wherein the temperature T(t=t 0 ) is captured at approximately a desired initial operating condition after commencement of an operational pulse of the power amplifier.
8. The invention of claim 2 , wherein the temperature T(t=t 0 ) is captured approximately when the power amplifier reaches peak Gain after commencement of an operational pulse of the power amplifier.
9. The invention of claim 2 , wherein at least one value of the temperature T(t>t 0 ) is captured within about 4 mS after commencement of an operational pulse of the power amplifier.
10. The invention of claim 2 , wherein the temperature T(t=t 0 ) is captured approximately when the power amplifier reaches peak Gain after commencement of an operational pulse of the power amplifier, and at least one value of the temperature T(t>t 0 ) is captured within about 4 mS after commencement of the operational pulse of the power amplifier.
11. An integrated circuit including (1) a WiFi power amplifier having a Gain that droops due to heating of the WiFi power amplifier during pulsed operation, and (2) a temperature compensation circuit, the temperature compensation circuit including:
(a) at least one sensor located with respect to the WiFi power amplifier so as to measure the temperature of the WiFi power amplifier and generate an output signal T representing such temperature;
(b) at least one sample and hold circuit, each coupled to at least one sensor through an intermediate amplifier coupled between the at least one sensor and the at least one sample and hold circuit, configured to capture a temperature T(t=t 0 ) at a time t 0 after commencement of pulsed operation of the WiFi power amplifier, and to sample a temperature T(t>t 0 ) at times after time t 0 ;
(c) a comparison circuit, coupled to at least one sample and hold circuit, for determining a signal ΔT=T(t>t 0 )−T(t=t 0 ); and
(d) a mapping circuit, coupled to the comparison circuit, for receiving values of the signal ΔT and mapping the values of the signal ΔT to corresponding control signal values, the control signal values being coupled to one or more adjustable circuits to adjust one or more circuit parameters of the one or more adjustable circuits.
12. The invention of claim 11 , wherein each pulse of pulsed operation of the WiFi power amplifier corresponds to a WiFi long packet.
13. The invention of claim 11 , wherein the control signal values maintain the Gain of the WiFi power amplifier within about ±0.05 dB during at least a 4 mS operational pulse of the WiFi power amplifier.
14. The invention of claim 11 , wherein the temperature T(t=t 0 ) is captured within about 10 μS after commencement of an operational pulse of the WiFi power amplifier.
15. The invention of claim 11 , wherein the temperature T(t=t 0 ) is captured at approximately a desired initial operating condition after commencement of an operational pulse of the WiFi power amplifier.
16. The invention of claim 11 , wherein the temperature T(t=t 0 ) is captured approximately when the WiFi power amplifier reaches peak Gain after commencement of an operational pulse of the WiFi power amplifier.
17. The invention of claim 11 , wherein at least one value of the temperature T(t>t 0 ) is captured within about 4 mS after commencement of an operational pulse of the WiFi power amplifier.
18. The invention of claim 11 , wherein the temperature T(t=t 0 ) is captured approximately when the WiFi power amplifier reaches peak Gain after commencement of an operational pulse of the WiFi power amplifier, and at least one value of the temperature T(t>t 0 ) is captured within about 4 mS after commencement of the operational pulse of the WiFi power amplifier.