A synchronized two-phase sinewave generator for AC metrology system compensations

A slave audio two-phase sinewave generator, which can be directly synchronized to a master generator, is described here. It can be used in ac metrology setups to provide additional “compensation” signals, traditionally derived with expensive multidecade inductive voltage divider networks. The generator is based on two direct digital synthesis (DDS) chips, programmed via the parallel printer PC interface; their clock is provided by a phase-locked loop circuit, which ensures frequency and phase synchronization of the DDS outputs with the master generator. The synchronization reference signal can be provided via an optical link reference channel, which avoids interference and ground loops. In its present implementation, the output voltage is Vpeak = 10 V, frequency range 500 Hz–4 kHz. Total harmonic distortion is contained to 65 dB, and amplitude stability is better than 500 V/V over 24 h.