Abstract: The circuit derives a rate signal from an a.c. signal proportional to attitude displacement provided, for example, from the synchro pickoff of a vertical gyroscope or an inertial navigation system, the pickoff receiving power from the aircraft a.c. power supply. The a.c. attitude signal is passed through a first bandpass filter tuned to the frequency of the power supply. The a.c. power supply signal is passed through a second bandpass filter identical to the first whose output is used as the reference signal for first and second identical demodulation circuits which include first and second matched low pass filters respectively. The filtered a.c. attitude signal is applied to the first demodulator circuit and the filtered power supply signal is applied to the second. The output of the first demodulator circuit is applied to a line voltage compensator and the output from the second demodulator circuit is applied to a d.c.