High-accuracy two-phase digital generator with automatic ratio and phase control

The experimental study of a low-frequency sinusoidal two-phase generator with digital waveform synthesis is presented, whose main purpose is improving the stability and accuracy of the complex ratio between the output voltages. The improved performance is obtained by means of a filtering technique with low phase shift and an original automatic control based on an auxiliary generator which interlocks the two out-of-phase voltages through the ratio windings of a composite transformer. With a bandwidth of 5 mHz, a reduction of the rms instability to levels ranging from a few parts to below one part in 10⁷ has been achieved, for different dynamic settings of the control.