Circuit with a power amplifier and amplification method
View Patent ↗In a power amplification circuit an output signal is generated by combining the power of a first and second signal that have been amplified separately. An input signal is received that indicates a desired amplitude and phase of the output signal. A controllable phase shift circuit adapts the phase of first and second signals dependent on the desired amplitude, so that, when the signals with the adapted phases are combined, the resulting output signal will have an envelope with the desired amplitude. A time dependent common mode phase shift is applied to both the first and second signal. A control circuit selects the time dependent common mode phase shift as a function of the desired amplitude of the output signal, to compensate for envelope amplitude dependence of a common phase shift introduced by the amplification.
1. A circuit with a power amplifier, the circuit comprising:
a first amplifier circuit and a second amplifier circuit for amplifying a first and second signal respectively;
a combiner circuit coupled to outputs of the first and second amplifier circuits and configured to combine power from the first and second amplifier circuits to form an output signal with an envelope amplitude influenced by a phase relation between the first and second signals;
an input for receiving an input signal indicating a desired amplitude and phase of the output signal;
a controllable phase shift circuit configured to adapt a phase of the first and second signals; and
a control circuit coupled between the input and a control input of the controllable phase shift circuit and configured to control a time dependent common mode phase shift applied to both the first and second signals as a function of the desired amplitude indicated at the input.
2. A circuit according to claim 1 , wherein said function is a predetermined function of the desired amplitude that has values that compensate an output signal envelope amplitude dependence of phase shifts introduced by the amplifier circuits.
3. A circuit according to claim 1 , further comprising a splitter with a splitter input coupled to the input and a first splitter output and a second splitter output;
wherein the controllable phase shift circuit comprises a first phase shifter and a second phase shifter coupled between the first and second splitter outputs and the first and second amplifier circuits respectively, the control circuit being configured to control a difference between phase shifts applied by the first and second phase shifters to adapt said phase relation between the first and second signals on which the envelope amplitude of the output signal depends.
4. A circuit according to claim 3 , wherein the controllable phase shift circuit comprises a common mode phase shifter with a phase shifter input coupled to the input, the splitter being coupled between the common mode phase shifter and the first and second amplifier circuits, the control circuit having an output coupled to a phase control input of the common mode phase shifter.
5. A circuit according to claim 3 , wherein the control circuit is configured to control a common mode component of the phase shifts applied by the first and second phase shifters to change to common mode component as a function of the desired amplitude indicated at the input.
6. A circuit according to claim 1 , wherein the controller comprises a look-up table circuit storing values of control signals for controlling the common mode phase shift for a plurality of values of the desired amplitude.
7. A circuit according to claim 1 , wherein at least one of the first and second amplifier circuits comprises a controllable preamplifier circuit and a final amplifier circuit coupled in series, the controllable preamplifier circuit having a gain control input coupled to an output of the control circuit, the control circuit being configured to control a gain of the controllable preamplifier circuit dependent on the desired amplitude indicated at the input, and to set a direction and size of the time dependent common mode phase shift to values that make the time dependent common mode phase shift compensate a phase shift resulting from control of the gain of the controllable preamplifier circuit.
8. A circuit according to claim 1 , wherein the first and second amplifier circuits each comprise a controllable preamplifier circuit and a final amplifier circuit coupled in series, the controllable preamplifier circuits having gain control inputs coupled to outputs of the control circuit, the control circuit being configured to control gains of the controllable preamplifier circuits mutually differently dependent on the desired amplitude indicated at the input, keeping the output envelopes at the final amplifier circuit of the first and second amplifier circuits equal to a predetermined maximum value, at least when the desired amplitude is above a threshold value.
9. A circuit according to claim 1 , further comprising a signal generator coupled to the input for providing said input signal, the signal generator being configured to perform combined data dependent modulation of both the desired amplitude and phase of the input signal in conjunction with each other.
10. A power amplification method, the method comprising:
receiving an input signal indicating a desired amplitude and phase of an output signal;
applying a controllable phase shift circuit configured to adapt a phase of first and second signals;
amplifying a first signal and a second signal;
combining power from the first and second signals to form the output signal with an envelope amplitude dependent on a phase relation between the first and second signals;
wherein a time dependent common mode phase shift is applied to both the first and second signals, the time dependent common mode phase shift being controlled as a function of the desired amplitude indicated at the input, to common mode phase shift values that compensate envelope amplitude dependence of a common phase shift introduced by said amplifying.
11. A method according to claim 10 , wherein amplification gains applied to the first and second signals are adapted mutually differently dependent on the desired amplitude, with gain values that keep the output envelopes at the final amplifier circuit of the first and second amplifier circuits equal to a predetermined maximum value, at least when the desired amplitude is above a threshold value.