Radio frequency transmitter having an amplifier with power supply modulation
A circuit including a carrier amplifier having an input, an output, a first transistor coupled to a first power supply voltage terminal for receiving a modulated power supply voltage, and a second transistor coupled to a second power supply voltage terminal for receiving a fixed power supply voltage is provided. The circuit further includes a peaking amplifier having an input coupled to the input of the carrier amplifier and an output coupled to the output of the carrier amplifier.
1. A circuit comprising:
a carrier amplifier having an input, an output, a first transistor coupled to a first power supply voltage terminal for receiving a modulated power supply voltage, and a second transistor coupled to a second power supply voltage terminal for receiving a fixed power supply voltage; and
a peaking amplifier having an input coupled to the input of the carrier amplifier and an output coupled to the output of the carrier amplifier.
2. The circuit of claim 1 further comprising a power supply modulation circuit for providing the modulated power supply voltage in response to an envelope of an input signal provided to the circuit.
3. The circuit of claim 2 , wherein the power supply modulation circuit further comprises an envelope detector.
4. The circuit of claim 2 further comprising:
a baseband block for providing the input signal as in-phase and quadrature signals;
and wherein the power supply modulation circuit comprises:
a transfer function block for applying a transfer function to the in-phase and quadrature signals to produce an envelope signal corresponding to the envelope of the in-phase and quadrature signals;
a digital-to-analog converter for converting the envelope signal to an analog signal; and
an amplifier coupled to receive the analog signal, and in response, to provide the modulated power supply voltage.
5. The circuit of claim 4 , wherein the transfer function block comprises a look-up table.
6. The circuit of claim 4 , wherein the transfer function is approximated by a piece-wise linear response to produce the envelope signal.
7. The circuit of claim 4 , wherein the amplifier is further characterized as being one of a class S modulator or a DC-DC converter.
8. The circuit of claim 1 , wherein the first power supply voltage terminal is coupled to a drain of the first transistor, and the second power supply voltage terminal is coupled to a drain of the second transistor.
9. The circuit of claim 1 further comprising a gate bias modulation circuit for providing a modulated gate bias voltage to bias a transistor of the peaking amplifier in response to the input signal provided to the circuit.
10. The circuit of claim 9 , further comprising:
a baseband block for providing the input signal as in-phase and quadrature signals;
and wherein the gate bias modulation circuit comprises:
a transfer function block, for applying a transfer function to the in-phase and quadrature signals to produce an envelope signal corresponding to the envelope of the in-phase and quadrature signals;
a digital-to-analog converter for converting the envelope signal to an analog signal; and
an amplifier coupled to receive the analog signal, and in response, providing the modulated gate bias voltage.
11. A transmitter comprising:
a carrier amplifier having an input, an output, a first power supply voltage terminal coupled to a first transistor for receiving a modulated power supply voltage, and a second transistor coupled to a second power supply voltage terminal for receiving a fixed power supply voltage;
a peaking amplifier having an input coupled to the input of the carrier amplifier and an output coupled to the output of the carrier amplifier; and
a power supply modulation circuit for producing the modulated power supply voltage in response to an input signal provided to the transmitter.
12. The transmitter of claim 11 , wherein the power supply modulation circuit further comprises an envelope detector.
13. The transmitter of claim 11 further comprising:
a baseband block for providing the input signal as in-phase and quadrature signals;
and wherein the power supply modulation circuit comprises:
a transfer function block for applying a transfer function to the in-phase and quadrature signals to produce an envelope signal corresponding to an envelope of the in-phase and quadrature signals;
a digital-to-analog converter for converting the envelope signal to an analog signal; and
an amplifier coupled to receive the analog signal, and in response, to provide the modulated power supply voltage.
14. The transmitter of claim 11 further comprising a gate bias modulation circuit for providing a modulated gate bias voltage to bias a transistor of the peaking amplifier in response to the input signal provided to the transmitter.
15. The transmitter of claim 14 further comprising:
a baseband block for providing the input signal as in-phase and quadrature signals;
and wherein the gate bias modulation circuit comprises:
a transfer function block, for applying a transfer function to the in-phase and quadrature signals to produce an envelope signal corresponding to the envelope of the in-phase and quadrature signals;
a digital-to-analog converter for converting the envelope signal to an analog signal; and
an amplifier coupled to receive the analog signal, and in response, providing the modulated gate bias voltage.
16. In a circuit comprising a carrier amplifier and a peaking amplifier, the carrier amplifier having an input, an output, a first transistor, and a second transistor, the peaking amplifier having an input coupled to the input of the carrier amplifier and an output coupled to the output of the carrier amplifier, a method comprising:
receiving an input signal;
converting the input signal into in-phase and quadrature signals;
producing a first envelope signal by applying a first predetermined transfer function to the in-phase and quadrature signals;
amplifying the first envelope signal to produce an amplified first signal;
providing the amplified first signal to a first power supply voltage terminal coupled to the first transistor for powering the first transistor; and
providing a fixed power supply voltage to a second power supply voltage terminal coupled to the second transistor for powering the second transistor.
17. The method of claim 16 further comprising:
producing a second envelope signal by applying a second predetermined transfer function to the in-phase and quadrature signals;
amplifying the second envelope signal to produce an amplified second signal; and
providing the amplified second signal to bias a transistor gate of the peaking amplifier.
18. The method of claim 16 , wherein producing the first envelope signal comprises squaring an amplitude of each of the in-phase and quadrature signals and summing the squared amplitudes.
19. The method of claim 16 , wherein amplifying the first signal to produce an amplified first signal further comprises amplifying the first signal using one of either a class S modulator or a DC-DC converter.
20. The method of claim 16 , wherein the method is implemented in a transmitter.