Abstract: A phase lock loop RF modulator system including a phase lock loop circuit having a phase detector circuit responsive to an input reference signal and a feedback signal, an oscillator circuit responsive to the phase detector circuit for providing an output signal, a forward path from the phase detector circuit to the oscillator circuit, and a feedback path from the oscillator circuit to the phase detector circuit. The system also includes a first modulation port coupled to the feedback path, a second modulation port coupled to the forward path, and a gain mismatch detection circuit responsive to modulation data and a phase error between the reference signal and the feedback signal for providing an indicator output signal that represents the gain mismatch between the first modulation port and the second modulation port.