Method and apparatus for optimizing transmitter power efficiency
A transmitter for a mobile device utilizes at least one mapper to improve power efficiency while still meeting out of band spurious emissions and waveform quality requirements. An encoder and modulator generates an encoded and modulated transmit signal from an input signal and a DAC then generates an analog representation of the encoded and modulated transmit signal. An amplifier stage coupled to the DAC amplifies the analog representation of the encoded and modulated transmit signal to generate a transmission signal. The transmitter further comprises an amplifier control block that generates an amplifier control signal to adjust at least one parameter of the amplifier stage. The amplifier control block includes at least one mapper to determine the amplifier control signal based on a peak to average power ratio and an average transmit power of the transmission signal. Environmental and operating conditions of the transmitter may be accounted for in the mappers.
1. A transmitter for a mobile device, the transmitter comprising:
an amplifier stage coupled to the digital to analog converter and configured to amplify an analog representation of an encoded and modulated transmit signal to generate a transmission signal; and
an amplifier control block configured to generate an amplifier control signal for adjusting at least one parameter of the amplifier stage, the amplifier control signal being generated based on mapping a peak to average power ratio and an average transmit power of the transmission signal and wherein the amplifier control block is configured to operate synchronously with a change in an input signal, from which the encoded and modulated transmit signal is derived, to compensate for a step response in the transmission signal to the small change in the input signal.
2. The transmitter of claim 1 , wherein the amplifier control block comprises:
a first mapper configured to generate a first signal representative of the peak to average power ratio based on a type of the encoded and modulated transmit signal;
a second mapper configured to generate a second signal representative of the average transmit power of the transmission signal; and
a summer configured to generate the amplifier control signal by summing the first and second signals.
3. The transmitter of claim 1 , wherein the amplifier control block comprises a mapper having a plurality of stored arrays or look up tables corresponding to a plurality of different peak to average power ratios to generate a corresponding amplifier control signal based on the average transmit power of the transmission signal.
4. The transmitter of claim 3 , wherein the mapper is configured to generate the corresponding amplifier control signal further based on one or more environmental conditions in which the transmitter is operating and wherein the mapper is updated at a rate appropriate to the changing one or more environmental conditions.
5. The transmitter of claim 3 , wherein the mapper is configured to generate the corresponding amplifier control signal further based on one or more operating conditions of the transmitter.
6. The transmitter of claim 5 , wherein the operating conditions of the transmitter comprise transmit frequency and drive band.
7. The transmitter of claim 1 , wherein the amplifier stage comprises:
an automatic gain control amplifier coupled to an output of the digital to analog converter; and
a power amplifier coupled to an output of the automatic gain control amplifier, wherein the amplifier control signal is for adjusting at least one parameter of the power amplifier.
8. The transmitter of claim 7 , further comprising a gain control block configured to generate an automatic gain control signal for controlling gain in the automatic gain control amplifier based on an average transmit power indicator corresponding to the average transmit power of the transmission signal.
9. The transmitter of claim 8 , further comprising a gain control compensation block coupled to the gain control block in a feedback loop, wherein the gain control compensation block is configured to generate a gain correction factor for the gain control block based on the amplifier control signal, wherein the gain correction factor compensates for gain expansion in the power amplifier due to variation in supply voltage of the power amplifier.
10. The transmitter of claim 9 , wherein either the gain correction factor is applied to one of the average transmit power indicator provided to the gain controller to adjust the automatic gain control signal and the automatic gain control signal directly.
11. The transmitter of claim 9 , wherein the gain correction factor is an input to the gain control block, and the gain control block is configured to generate the automatic gain control signal based further on the gain correction factor.
12. The transmitter of claim 7 , wherein the at least one parameter of the power amplifier comprises at least one of a bias, a current bias, a supply voltage, a stage switch-in, a stage switch-out, a turning on, a turning off, a gain, a gain distribution, a conducting angle, an amplifier class change, a load, or an impedance.
13. The transmitter of claim 1 , wherein the amplifier control block comprises a plurality of mappers configured to determine a corresponding plurality of amplifier control signals based on the peak to average power ratio and the average transmit power of the transmission signal.
14. The transmitter of claim 1 , wherein at least one of the plurality of amplifier control signals is for adjusting a supply voltage or current bias of the amplifier stage.
15. The transmitter of claim 1 , wherein the amplifier control signal and the analog representation of the encoded and modulated transmit signal are delay aligned.
16. The transmitter of claim 1 , wherein the amplifier control signal is advanced in time with respect to the analog representation of the encoded and modulated transmit signal.
17. The transmitter of claim 1 , wherein the analog representation of the encoded and modulated transmit signal is delayed in time with respect to the amplifier control signal.
18. The transmitter of claim 1 , wherein at least one of the encoder and modulator, the digital to analog converter, and the amplifier stage has a stepped response; and wherein the at least one mapper comprises a plurality of stored arrays or look up tables; and further wherein one of the plurality of stored arrays or lookup tables is selected based on an input to the at least one of the encoder and modulator, the digital to analog converter, and the amplifier stage and the stepped response.
19. A method of optimizing power efficiency in an amplifier stage, the method comprising:
amplifying an analog representation of an encoded and modulated transmit signal in the amplifier stage to generate a transmission signal;
generating an amplifier control signal based on mapping a peak to average power ratio and an average transmit power of the transmission signal;
operating synchronously with a change in an input signal, from which the encoded and modulated transmit signal is derived, to compensate for a step response in the transmission signal to the small change in the input signal; and
adjusting at least one parameter of the amplifier stage using the amplifier control signal.
20. A computer-readable storage medium storing instructions executable by a processor coupled to the storage medium, the instructions for programming the processor, when executed, to perform the method of claim 19 .