Input drive control for switcher regulated power amplifier modules
Various embodiments described herein relate to a power management block and an amplification block used in the transmitter of a communication subsystem. The power management block provides improved control for the gain control signal provided to a pre-amplifier and the supply voltage provided to a power amplifier which are both in the amplification block. The power expended by the power amplifier is optimized by employing a continuous control method in which one or more feedback loops are employed to take into account various characteristics of the transmitter components and control values.
1. A control system for a transmitter of a wireless device, the transmitter having a pre-amplifier and a power amplifier coupled to an output of the pre-amplifier, the control system comprising:
a switching regulator control block configured to generate a switching supply control signal based on a pre-amplified transmission signal detected at the output of the pre-amplifier, the switching supply control signal comprising control values for controlling a switched mode power supply to generate a supply voltage signal for the power amplifier; and
a compensating control block configured to generate a gain correction signal based on the supply voltage signal and a rate of change of the supply voltage signal, the gain correction signal being used to adjust a gain control signal provided to the pre-amplifier for controlling gain in the pre-amplifier,
wherein the compensating control block has a compensating transfer function adapted to produce the gain correction signal to maintain a substantially linear relationship between the gain control signal and power of an amplified transmission signal produced by the power amplifier.
2. The control system of claim 1 , wherein the compensating transfer function is further adapted to postpone saturation effects of a relationship between the gain control signal and the power of the amplified transmission signal.
3. The control system of claim 1 , wherein the compensating transfer function is implemented in hardware by a filter and is adapted to compensate for static gain changes and dynamic variation due to lags in the pre-amplifier, the power amplifier and the control system.
4. The control system of claim 1 , further comprising:
a summer configured to subtract the gain correction signal from an automatic gain control signal to generate a modified automatic gain control signal; and
a power limit control block configured to generate the gain control signal based on the modified automatic gain control signal, the pre-amplified transmission signal, and a transmit power limit signal for limiting transmission power of the transmitter.
5. The control system of claim 4 , wherein the power limit control block is configured to anticipate and correct an over-power condition by modifying the pre-amplifier gain.
6. The control system of claim 4 , further comprising a detector coupled to an output of the pre-amplifier to provide a detected pre-amp output signal and wherein the power limit control block comprises:
a clipper configured to produce a clipped power error signal by converting negative values of a power error signal to zero and multiplying positive values of the power error signal by an adjustment factor, the power error signal being produced by subtracting the transmit power limit signal from the detected pre-amp output signal;
an integrator configured to integrate the clipped power error signal to produce an integrated power error signal; and
a power limiting transfer function configured to process the integrated power error signal to detect the over-power condition before this condition occurs and to generate an error signal,
wherein the gain control signal is generated by subtracting the error signal from the modified automatic gain control signal.
7. The control system of claim 1 , wherein at least one of the switching regulator control block and the compensating control block are implemented in a processor.
8. The control system of claim 1 , wherein the switching regulator control block is configured to apply a switching control transfer function.
9. The control system of claim 8 , wherein at least one the compensating transfer function and the switching control transfer function is defined in a processor using one or more look-up tables.
10. The control system of claim 4 , wherein the power limit control block is implemented in a processor and is configured to apply a transfer function defined in the processor using one or more look-up tables to generate the gain control signal.
11. A method of controlling a transmitter of a wireless device using a control system, the transmitter having a pre-amplifier and a power amplifier coupled to an output of the pre-amplifier, the method comprising:
generating a switching supply control signal based on a pre-amplified transmission signal detected at the output of the pre-amplifier, the switching supply control signal comprising control values for controlling a switched mode power supply;
providing the switching supply control signal to the switched mode power supply to generate a supply voltage signal for the power amplifier;
generating a gain correction signal based on the supply voltage signal and a rate of change of the supply voltage signal;
adjusting a gain control signal using the gain correction signal, the gain control signal for controlling gain in the pre-amplifier; and
providing the gain control signal to the pre-amplifier,
wherein the gain correction signal is generated using a compensating transfer function to maintain a substantially linear relationship between the gain control signal and power of an amplified transmission signal produced by the power amplifier.
12. The method of claim 11 , further comprising adapting the compensating transfer function to postpone saturation effects of a relationship between the gain control signal and the power of the amplified transmission signal.
13. The method of claim 11 , further comprising adapting the compensating transfer function to compensate for static gain changes and dynamic variation due to lags in the pre-amplifier, the power amplifier and the control system.
14. The method of claim 11 , further comprising
subtracting the gain correction signal from an automatic gain control signal to generate a modified automatic gain control signal; and
generating the gain control signal based on the modified automatic gain control signal, the pre-amplified transmission signal, and a transmit power limit signal for limiting transmission power of the transmitter.
15. The method of claim 14 , further comprising anticipating an over-power condition and modifying the pre-amplifier gain to correct for the over-power condition.
16. The method of claim 15 , further comprising:
detecting an output of the pre-amplifier to provide a detected pre-amp output signal;
producing a power error signal by subtracting the transmit power limit signal from the detected pre-amp output signal;
clipping the power error signal to produce a clipped power error signal by converting negative values of the power error signal to zero and multiplying positive values of the power error signal by an adjustment factor;
integrating the clipped power error signal to produce an integrated power error signal;
processing the integrated power error signal with a power limiting transfer function to detect the over-power condition before this condition occurs and to generate an error signal; and
generating the gain control signal by subtracting the error signal from the modified automatic gain control signal.
17. The method of claim 11 , wherein at least one of the switching supply control signal and the gain correction signal are generated in a processor.
18. The method of claim 11 , further comprising defining the transfer function in the processor using one or more look-up tables.
19. The method of claim 10 , wherein the gain control signal is generated in a processor and the method further comprises applying a transfer function defined in the processor using one or more look-up tables to generate the gain control signal.