Automatisk kalibrering af bærebølgeundertrykkelse og sløjfefase i en kartesisk forstærker

A transmitter comprises an input terminal for receiving a signal to be amplified, a forward amplification path having a power amplifier output stage and a feedback path used to improve linearity, having two modes of operation: A) during a first mode of operation: i) at least occasionally measuring the DC conditions within the transmitter with the power amplifier disabled and using the results to minimise carrier output from the transmitter; ii) at least occasionally measuring the phase shift around the feedback loop required to achieve negative feedback; B) during a second mode of operation, using the measurement of phase shift to ensure negative feedback by applying phase compensation.