Broadband high efficiency amplifier system incorporating dynamic modulation of load impedance
View Patent ↗Systems and methods are provided for producing an amplified radio frequency (RF) signal representing a baseband input signal. A first amplifier amplifies a first intermediate signal to provide a first amplified signal. Second and third amplifiers amplify a second intermediate signal to provide second and third amplified signals. A signal combiner combines the first, second, and third amplified signals to produce the amplified RF signal. An RF modulator modulates an RF carrier signal with a baseband input signal to provide the first and second intermediate signals. The RF modulator provides the first and second intermediate signals such that the first amplified signal is out-of-phase with each of the second and third amplified signals at an output of an active device within the second amplifier when the amplitude of the baseband input signal exceeds a threshold voltage and in phase when the baseband input signal is below a threshold voltage.
1. A system for providing an amplified radio frequency (RF) signal representing a baseband input signal, the system comprising:
a first amplifier, on a first signal path, configured to amplify a first intermediate signal to provide a first amplified signal;
a second amplifier, on a second signal path, configured to amplify a second intermediate signal to provide a second amplified signal;
a third amplifier, on the second signal path, configured to amplify the second intermediate signal to provide a third amplified signal;
a signal combiner configured to combine the first amplified signal, the second amplified signal, and the third amplified signal to produce the amplified RF signal; and
an RF modulator configured to modulate an RF carrier signal with a baseband input signal to provide the first intermediate signal on a first signal path and the second intermediate signal on the second signal path, the RF modulator providing the first and second intermediate signals such that the first amplified signal is out-of-phase with each of the second and third amplified signals at an output of an active device within the second amplifier when the amplitude of the baseband input signal exceeds a first threshold voltage and the first amplified signal is in phase with each of the second and third amplified signals at the output of the active device within the second amplifier when the baseband input signal is below the first threshold voltage;
wherein the RF modulator is further configured to provide the second intermediate signal only when the baseband input signal amplitude is above a second threshold voltage, higher than the first threshold voltage, such that the first amplifier is active and the second and third amplifiers are not active, and to provide the first intermediate signal to the first amplifier such that the amplitude of the first amplified signal increases substantially linearly with the amplitude of the baseband input signal when the amplitude of the baseband input signal is below the first threshold voltage, decreases as the amplitude of the baseband input signal increases when the amplitude of the baseband input signal is between the first threshold voltage and the second threshold voltage, and increases, but is out-of-phase with each of the second and third amplified signals, when the amplitude of the baseband input signal exceeds the second threshold voltage.
2. The system of claim 1 , the RF modulator being configured to provide the second intermediate signal to the second and third amplifiers such that the amplitude of the second and third amplified signals each vary substantially linearly with the amplitude of the baseband input signal when the amplitude of the baseband input signal is between the first threshold voltage and the second threshold voltage, and second and third amplifiers operate in saturation when the amplitude of the baseband input signal exceeds the second threshold voltage.
3. The system of claim 1 , the RF modulator being configured to.
4. The system of claim 1 , the RF modulator being configured, when the amplitude of the baseband input signal is below the first threshold voltage, to provide the first intermediate signal to the first amplifier such that the amplitude of the first amplified signal is equal to the product of the amplitude of the baseband input signal and an amplitude response of the system, wherein the amplitude response of the system is determined as a linear combination of respective saturation voltages of the first, second, and third amplifiers divided by a peak voltage of the baseband input signal.
5. The system of claim 1 , wherein the threshold voltage is proportional to a ratio of a saturation voltage of the first amplifier to an amplitude response of the system, wherein the amplitude response of the system is determined as a linear combination of respective saturation voltages of the first and second amplifiers divided by a peak voltage of the baseband input signal.
6. The system of claim 1 , the first amplifier being biased in class AB and each of the second and third amplifiers being biased in class C.
7. The system of claim 1 , the signal combiner comprising a quadrature combiner, the first amplified signal being provided to an isolation port of the quadrature combiner and the second and third amplified signals being provided to respective through and coupled ports of the quadrature combiner.
8. The system of claim 1 , wherein the signal combiner is configured such that a load impedance at the output of the active device within the second amplifier is modulated by the first amplified signal.
9. The system of claim 1 , further comprising a 3 dB quadrature signal splitter configured to distribute the second intermediate signal to the second and third amplifiers.