Abstract: An AC signal source having constant frequency-amplitude product is also easily realizable in hybrid microcircuit form. A square wave oscillator output is rectified and clamped to a feedback control voltage. The resulting controlled amplitude square wave is low-pass filtered to produce a sinusoidal output signal which is typically amplified and applied to a variable-impedance load. The sinusoidal signal is also applied to a similar but simulated load of fixed impedance value and the current flowing through the simulated load is summed with a temperature-compensated reference current producing an error current which is then integrated to produce the feedback control voltage which controls the amplitude of the sinusoidal signal so as to maintain a constant frequency amplitude product.