Characterization of a Wideband Digitizer for Power Measurements up to 1 MHz

Abstract

A two-channel high-speed digitizer has been extensively characterized in the frequency range of 50 Hz-1 MHz. Measurements involved alternating-current (ac) flatness, phase, linearity, input impedance, and the effects of direct-current offsets, temperature, and an internal self-calibration routine. A digital antialiasing filter inside the digitizer negatively affects ac flatness in the low-frequency region. An inverse compensation filter has been designed and applied, which improves frequency response with a factor of 25-60 and makes it flat within 25 μV/V up to 100 kHz and within 100 μV/V up to 1 MHz. The phase difference between the two channels can be modeled by a constant time delay between the two channels, which for the 2- V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</sub> range equals (250 ± 30) ps. The overall results of the characterization indicate that the digitizer can be applied in wideband power measurements under practical circumstances with ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> = 1) uncertainty contributions of not more than 70 and 400 μW/VA at 10 kHz and 1 MHz, respectively. This uncertainty excludes loading effects, which are significant at frequencies above 100 kHz. At low frequencies, up to three times lower uncertainty are achieved when the digitizer is calibrated at the signal level and temperature at which it is subsequently used.