Synthesizing signal generator for use with lock-in amplifiers in audiofrequency measurements

Lock-in amplifiers may be used to measure audiofrequency signals with linearity errors of 10
⁻³
or less. Accuracy is often limited, however, by errors of 1–2 percent in the quadrature separation of the lock-in's polarizing signals. A signal generator is described which in the range 31 Hz–8 kHz provides sinusoidal measuring signals together with a square-wave signal which may be phase-shifted in precise steps of 90°. With this square wave as the external reference of a lock-in, signals may be resolved into orthogonal components with accuracies of 1 in 10
⁴
. The generator is programmable, and so permits sequences of measurements to be executed under computer control.