Current saving by reduced modulation code and selective gating of RF signal
A polar modulation power amplifier employs both thermometer coded and binary coded amplitude modulation data. The thermometer coded amplitude modulation data selectively activates one or more equally weighted power amplifier cells. The binary coded amplitude modulation data selectively activates one or more binary weighted power amplifier cells. When less than full output power is required and the MSBs of the amplitude modulation data are zero (reducing output power at the expense of quantization noise), the power dissipated by RF signal buffers for the unused power amplifier cells corresponding to the MSBs is substantially reduced by gating off the RF signal upstream of the buffers.
1. A method of reducing power consumption in a wireless communication transmitter power amplifier, comprising:
providing a phase-modulated radio frequency periodic signal to a plurality of power amplifier cells;
receiving digital amplitude modulation data;
thermometer coding a first plurality of the modulation data bits;
selectively activating one or more equally weighted power amplifier cells based on the thermometer coded modulation data bits;
binary coding a second plurality of the modulation data bits;
selectively activating one or more binary weighted power amplifier cells based on the binary coded modulation data bits;
receiving an output power requirement indication;
if the output power requirement exceeds a predetermined threshold, enabling the phase-modulated radio frequency periodic signal to all of the power amplifier cells; and
if the output power requirement is less than the threshold, selectively gating the phase-modulated radio frequency periodic signal upstream of one or more final buffers associated with inactive power amplifier cells, to eliminate switching current in the buffers.
2. The method of claim 1 wherein selectively activating one or more equally weighted power amplifier cells based on the thermometer coded modulation data bits comprises selectively activating a plurality of equally weighted power amplifier cells based on the thermometer coded modulation data bits.
3. The method of claim 1 wherein selectively activating one or more binary weighted power amplifier cells based on the thermometer coded modulation data bits comprises selectively activating a plurality of binary weighted power amplifier cells based on the thermometer coded modulation data bits.
4. The method of claim 1 wherein the current through each power amplifier cell is regulated by a cascode transistor, and further comprising, if the output power requirement is less than the threshold, adjusting the current through the active power amplifier cells via the cascode transistor to maintain a desired output power.
5. The method of claim 1 wherein the first plurality of the modulation data bits comprise the most significant bits of the modulation data and the second plurality of the modulation data bits comprise the least significant bits of the modulation data.
6. The method of claim 1 wherein selectively gating the phase-modulated radio frequency periodic signal upstream of one or more final buffers comprises
providing digital power amplifier cell enable data; and
wherein providing a phase-modulated radio frequency periodic signal to a plurality of power amplifier cells comprises logically gating the phase-modulated radio frequency periodic signal with each bit of the digital power amplifier cell enable data and providing each gated phase-modulated radio frequency periodic signal to each power amplifier cell.
7. The method of claim 1 wherein
the plurality of power amplifier cells is nineteen cells;
the digital amplitude modulation data is 8 bits;
the first plurality of thermometer coded modulation data bits is 15 bits and the plurality of equally weighted power amplifier cells is 15 cells; and
the second plurality of binary coded modulation data bits is 4 bits and the plurality of binary weighted power amplifier cells is 4 cells.
8. The method of claim 7 wherein the 15 evenly weighted power amplifier cells have a weight of 16, and the 4 binary weighted power amplifier cells have weights of 8, 4, 2, and 1.
9. A power amplifier output stage for a wireless communication transmitter, comprising:
control circuits operative to receive digital amplitude modulation data and an output power requirement indication, and generate digital power amplifier cell enable data;
a plurality of gating signal drivers operative to receive a phase-modulated radio frequency periodic signal, and to generate a plurality of gated phase-modulated radio frequency periodic signals, each gating signal drivers including
a final buffer; and
a logic gate upstream of the final buffer, the logic gate receiving the phase-modulated radio frequency periodic signal and one bit of the digital power amplifier cell enable data;
an encoder operative to thermometer code a first plurality of the modulation data bits and to binary code a second plurality of the modulation data bits;
a plurality of evenly weighted power amplifier cells each adapted to receive a corresponding one of the plurality of gated phase-modulated radio frequency periodic signal and a thermometer coded modulation data bit, and operative to selectively amplify the gated phase-modulated radio frequency periodic signal if activated by the thermometer coded modulation data bit; and
a plurality of binary weighted power amplifier cells each adapted to receive a corresponding one of the plurality of gated phase-modulated radio frequency periodic signal and a binary coded modulation data bit, and operative to selectively amplify the gated phase-modulated radio frequency periodic signal if activated by the binary coded modulation data bit;
wherein the control circuits are further operative to selectively gate the phase-modulated radio frequency periodic signal upstream of the final buffer via the digital power amplifier cell enable data if the output power requirement is less than a threshold, to eliminate switching current in the final buffer.
10. The amplifier output stage of claim 9 further comprising a cascode transistor operative to regulate the current through each power amplifier cell, and wherein the control circuits are further operative, if the output power requirement is less than the threshold, to adjust the current through the active power amplifier cells via the cascode transistor to maintain a desired output power.
11. The amplifier output stage of claim 9 wherein the first plurality of the modulation data bits comprise the most significant bits of the modulation data and the second plurality of the modulation data bits comprise the least significant bits of the modulation data.
12. The amplifier output stage of claim 9 wherein
the first plurality of thermometer coded modulation data bits is 15 bits and the plurality of evenly weighted power amplifier cells is 15 cells;
the second plurality of binary coded modulation data bits is 4 bits and the plurality of binary weighted power amplifier cells is 4 cells;
the digital amplitude modulation data is 8 bits; and
the digital power amplifier cell enable data is 19 bits.
13. The amplifier output stage of claim 12 wherein the 15 evenly weighted power amplifier cells have a weight of 16, and the 4 binary weighted power amplifier cells have weights of 8, 4, 2, and 1.