Absolute power detector
View Patent ↗A method and apparatus is provided for detecting the output power of a power amplifier. The output power is detected by detecting the absolute values of the voltage and current at the output of the amplifier and mixing the detected voltage and current to generate a signal related to the output power.
1. An RF power amplifier for a wireless communication system comprising:
a power amplifier having an output, the output of the power amplifier having an output power range over which the power amplifier operates;
a voltage sensor coupled to the power amplifier for sensing the voltage at the output of the power amplifier, wherein the voltage sensor includes a logarithmic amplifier;
a current sensor coupled to the power amplifier for sensing the current at the output of the power amplifier; and
a circuit coupled to the voltage sensor and current sensor for controlling the output power of the power amplifier, wherein the circuit actively controls the output power of the power amplifier over substantially the entire output power range of the power amplifier by generating a signal based on the magnitudes of the voltage and current at the output of the power amplifier, and wherein the signal is proportional to the output power of the power amplifier such that changes in the magnitudes of the voltage and current at the output of the power amplifier will cause the gain of the power amplifier to be adjusted proportionally over substantially the entire output power range of the power amplifier.
2. The RF power amplifier of claim 1 , further comprising a first envelope detector coupled to the voltage sensor for determining the magnitude of the sensed voltage.
3. The RF power amplifier of claim 2 , further comprising a second envelope detector coupled to the current sensor for determining the magnitude of the sensed current.
4. The RF power amplifier of claim 1 , wherein the voltage sensor is comprised of a voltage divider coupled to the output of the power amplifier.
5. The RF power amplifier of claim 2 , wherein the voltage sensor is comprised of a direct connection between the output of the power amplifier and the first envelope detector.
6. The RF power amplifier of claim 1 , wherein the current sensor is comprised of first and second mutually coupled inductors.
7. The RF power amplifier of claim 6 , wherein the first mutually coupled inductor is connected to the output of the power amplifier, and wherein the current is sensed by sensing the induced current in the second inductor.
8. The RF power amplifier of claim 6 , wherein the first mutually coupled inductor is comprised of a filter inductor of the power amplifier.
9. The RF power amplifier of claim 1 , wherein the current sensor is comprised of circuitry that senses a voltage drop across an impedance connected between the output of the power amplifier and a load.
10. A circuit for controlling the output power of an RF power amplifier used with a wireless communication system comprising:
circuitry for sensing the voltage at the output of the RF power amplifier;
circuitry for determining the magnitude of the sensed voltage;
circuitry for sensing the current at the output of the RF power amplifier;
circuitry for determining the magnitude of the sensed current; and
circuitry for generating a control signal for controlling the output power of an RF power amplifier based on the magnitude of the voltage at the output of the RF power amplifier and the magnitude of the current at the output of the RF power amplifier, wherein the circuitry for generating a control signal includes a summing element coupled to the circuitry for determining the magnitude of the sensed voltage and the circuitry for determining the magnitude of the sensed current, wherein the output power of the RF power amplifier is actively controlled based on the magnitude of the voltage at the output of the RF power amplifier and the magnitude of the current at the output of the RF power amplifier over substantially the entire output power range of the RF power amplifier, and wherein the control signal is proportional to the output power of the power amplifier such that changes in the magnitudes of the voltage and current at the output of the power amplifier will cause the gain of the power amplifier to be adjusted proportionally over substantially the entire output power range of the power amplifier.
11. The circuit of claim 10 , wherein the circuitry for determining the magnitude of the sensed voltage comprises a first envelope detector.
12. The circuit of claim 11 , wherein the circuitry for determining the magnitude of the sensed current comprises a second envelope detector.
13. A method of controlling the output power of an RF power amplifier used with a wireless communication system, the method comprising:
sensing the magnitude of the voltage at the output of the power amplifier;
sensing the magnitude of the current at the output of the power amplifier;
generating a control signal based on the sensed magnitudes of the voltage and current, wherein the control signal is proportional to the output power of the power amplifier, wherein the control signal is generated by combining the outputs of first and second logarithmic amplifiers; and
controlling the output power of the power amplifier based on the control signal and a desired output power level, wherein the output power of the power amplifier is actively controlled using the sensed magnitudes of the voltage and current over substantially the entire operating ranges of the sensed magnitudes of the voltage and current such that changes in the magnitudes of the voltage and current at the output of the power amplifier will cause the gain of the power amplifier to be adjusted proportionally over substantially the entire output power range of the power amplifier.
14. The method of claim 13 , wherein the magnitude of the voltage is sensed using a first envelope detector.
15. The method of claim 14 , wherein the magnitude of the current is sensed using a second envelope detector.
16. The method of claim 13 , wherein the magnitude of the voltage is sensed using a voltage divider.
17. The method of claim 13 , wherein the magnitude of the current is sensed using first and second mutually coupled inductors.
18. The method of claim 13 , wherein the magnitude of the current is sensed by detecting a voltage drop across an impedance element coupled to the output of the power amplifier.