Method and apparatus for adaptive transmit power control

1. A transceiver comprising:

a variable gain power amplifier (PA), the PA configured to receive a signal to be transmitted, and provide gain to the signal to be transmitted;

a circuit comprising:

a first resistor having a first and second terminal, the first terminal of the first resistor coupled to an output of the PA;

a switch having a first and second terminal, the second terminal of the first resistor coupled to the first terminal of the switch; and

a second resistor having a first and second terminal, the first terminal of the second resistor coupled to the second terminal of the switch and the second terminal of the second resistor coupled to an input to a low noise amplifier (LNA); and

a control module that is:

coupled to the PA and to an output of the circuit; and

configured to:

provide the signal to be transmitted to the PA;

measure whether distortion to the signal coupled from the output of the circuit is above an acceptable limit;

if the amount of distortion is below the acceptable limit, provide a signal to the PA to increase the gain provided by the PA; and

if the amount of distortion is above the acceptable limit, reduce the gain provided by the PA.

2. The transceiver of claim 1 , comprising:

a) a transmit block, wherein signals coupled from the control module to an input of the PA are coupled through the transmit block; and

b) wherein signals coupled from the circuit to the control module are coupled through the LNA.

3. The transceiver of claim 2 , comprising a receive block, wherein signals coupled between the LNA and the control module are coupled through the receive block.

4. The transceiver of claim 2 , comprising a transmit/receive (T/R) switch having a first input/output (I/O) terminal, a second I/O terminal and a common terminal, the first I/O terminal coupled to the output of the PA, the second I/O terminal coupled to an input of the LNA and the common terminal switchable to make connection with either the first I/O terminal or the second I/O terminal and wherein the circuit is formed by the leakage from the first I/O terminal to the second I/O terminal between the output of the PA and the input of the LNA.

5. The transceiver of claim 1 , wherein the control module is configured to provide a test signal to the PA to be transmitted during times at which transmission of test signals will not interfere with operations of a network.

6. The transceiver of claim 1 , wherein the control module is configured to: (i) receive information intended to be transmitted to a receiver over a network; (ii) modulate the information; and (iii) couple the modulated information to the PA.

7. The transceiver of claim 1 , wherein the distortion measurement comprises a measurement of the amount of amplitude compression in the peak amplitude of a loop-back signal.

8. The transceiver of claim 2 , wherein:

the transmit block includes a pre-amplifier;

the control module is configured to:

set a gain of the pre-amplifier independent of the PA based on the determination of whether the distortion to the signal coupled from the output of the circuit is above the acceptable limit, wherein:

if the distortion to the signal coupled from the output of the circuit is above the acceptable limit, the gain provided by the pre-amplifier is increased; and

if the distortion to the signal coupled from the output of the circuit is below the acceptable limit, the gain provided by the pre-amplifier is decreased.

9. The transceiver of claim 3 , wherein:

the receive block includes a digital to analog converter (DAC); the control module is configured to:

control a gain of digital inputs to the DAC; set the gain of the digital inputs to the DAC independent of the PA based on the determination of whether the distortion to the signal coupled from the output of the circuit is above the acceptable limit, wherein:

if the distortion to the signal coupled from the output of the circuit is above the acceptable limit, the gain of the digital inputs to the DAC is decreased; and

if the distortion to the signal coupled from the output of the circuit is below the acceptable limit, the gain of the digital inputs to the DAC is increased.

10. A method for adjusting the gain of a transmitter, the method comprising:

amplifying a transmit signal with an adjustable gain power amplifier (PA);

communicating a loopback signal, based on said amplified transmit signal, to an input of a low noise amplifier (LNA) using a first resistor coupled to an output of said PA and to a second resistor, said second resistor coupled to said input of said LNA;

measuring the amount of distortion in said loop-back signal while transmitting the amplified transmit signal to an operational load, wherein:

an output of the LNA is coupled to a distortion measurement module that is configured to determine whether the distortion in the loop-back signal is less than a limit; and

if the amount of distortion that is measured is less than the limit, increasing the gain of the PA, otherwise decreasing the gain of the PA.

11. The method of claim 10 , wherein the distortion measurement is made based on measurements of a peak amplitude of the loop-back signal.

12. The method of claim 10 , comprising performing said amplifying and measuring for each component of a transmit chain for which gain of the component can be adjusted.

13. The method of claim 10 , comprising transmitting the transmit signal to an operational load while measuring distortion on the loop-back signal.

14. The method of claim 10 , wherein the distortion measurement is made based on measurements of a peak to average ratio of the loop-back signal.

15. The method of claim 10 , wherein the distortion measurement is made based on amplitude compression in a peak amplitude of the loop-back signal.

16. The method of claim 10 , wherein the distortion measurement is made based on both phase compression and amplitude compression in a peak amplitude of the loop-back signal.

17. The method of claim 10 , wherein the distortion measurement is made based on transmit modulation error rate (MER) for the loop-back signal.

18. The method of claim 10 , wherein the transmit signal is a test tone that is an orthogonal frequency division multiplexed (OFDM) signal comprising a plurality of carriers upon which test data is modulated.

19. The method of claim 10 , wherein the transmit signal comprises live transmit signals modulated with information intended for reception by a receiver.

20. A transceiver comprising:

a variable gain power amplifier (PA), the PA configured to receive a signal to be transmitted, and provide gain to the signal to be transmitted;

a loopback circuit comprising a switch and first and second resistors, each having a first terminal and a second terminal, the first terminal of the first resistor coupled to an output of the PA, the second terminal of the first resistor coupled to the first terminal of the switch, the first terminal of the second resistor coupled to the second terminal of the switch, and the second terminal of the second resistor coupled to a low noise amplifier;

a control module that is:

coupled to the PA and to an output of the loopback circuit; and

configured to:

provide the signal to be transmitted to the PA;

measure whether distortion to the signal coupled from the output of the loopback circuit is above an acceptable limit, wherein distortion is measured by measuring the amount of amplitude compression in the peak amplitude of a loop-back signal;

if the amount of distortion is below the acceptable limit, provide a signal to the PA to increase the gain provided by the PA; and

if the amount of distortion is above the acceptable limit, reduce the gain provided by the PA.