Patent ID: 8749273

Claim:
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.