Power amplifier saturation detection

摘要

In a portable radio transceiver, a power amplifier system includes a saturation detector that detects power amplifier saturation in response to duty cycle of the amplifier transistor collector voltage waveform. The saturation detection output signal can be used by a power control circuit to back off or reduce the amplification level of the power amplifier to avoid power amplifier control loop saturation.

主权项

1. A power amplifier circuit for a radio frequency (RF) transmitter, the power amplifier circuit comprising:
a power amplifier including a first output transistor and a second output transistor, the first output transistor including a first output transistor terminal coupled to a first supply voltage, and the second output transistor including a second output transistor terminal coupled to a second supply voltage; a first duty cycle detector including: a first input coupled to the first output transistor terminal; a first limiter coupled to the first output transistor terminal, and configured to block positive voltage excursions and to pass negative voltage excursions; and a first averaging filter coupled to an output of the first limiter; a second duty cycle detector including: a second input coupled to the second output transistor terminal; a second limiter coupled to the second output transistor terminal, and configured to block positive voltage excursions and to pass negative voltage excursions; and a second averaging filter coupled to an output of the second limiter; and a comparator circuit configured to produce a saturation detection output signal, the comparator circuit including a first input and a second input, the first input configured to be coupled to one of the first duty cycle detector and the second duty cycle detector, and the second input coupled to a reference voltage circuit.