A low-noise latching comparator probe for waveform sampling applications

A new latching comparator probe is described. The probe is being developed as part of an effort to augment voltage measurement capability in the 10 Hz to 1 MHz frequency range. The probe offers an input voltage range of /spl plusmn/10 V, input impedance of 1 M/spl Omega/ and root mean square noise referred to the input as low as 55 /spl mu/V. The probe's 3-dB bandwidth is approximately 20 MHz. Total harmonic distortion is as low as -93 dB at 50 kHz. Gain flatness is within /spl plusmn/10 /spl mu/V/V from 100 Hz to 100 kHz. Improved step settling performance is achieved using a technique that minimizes circuit thermal errors. The probe's input range can be extended with a frequency-compensated 1-M/spl Omega/ input impedance attenuator allowing measurement of pulses in the microsecond regime up to 100 V. The attenuator can be compensated further with a digital filtering algorithm to achieve gain accuracy better than 100 /spl mu/V/V.