Polyharmonic Digital Synthesis for the calibration of phase sensitive measuring systems up to the ultrasonic band

A double output digital polyharmonic synthesizer suitable for the calibration of phase sensitive measuring systems and harmonics in power analyzers is being developed at INRIM. Digital-to-analog converters with high resolution and update rate simultaneously synthesize a pair of waveforms with fine trimming of electric parameters and harmonics. Its bandwidth is up to 100 MHz, verified with a wideband sampling oscilloscope, and the frequency resolution is 20mHz in the whole bandwidth. The synthesizer has been characterized in terms of amplitude, accuracy, and stability up to 1MHz by means of a programmable ac/dc transfer standard. For frequencies up to 100 kHz, a calibrated precision digitizer, configured as a phase comparator, is used for its characterization. The measured phase offset and noise at 20 kHz are 5 μrad and 300 nrad, respectively. The same digitizer has been used for the precise measure of the harmonic spurs up to 100 kHz. Instead, for the evaluation of the total harmonic distortion from 100 kHz up to 50 MHz, a wideband spectrum analyzer has been used. The algorithms employed allow the use of the synthesizer as a digital phase standard or as a polyharmonic arbitrary synthesizer with independent outputs.