The circuit employs an input transconductance amplifier capable of providing large amounts of charging current to the holding capacitor, thus enabling fast acquisition times. It also incorporates a low leakage analog switch and an output integrating amplifier with input bias current optimized to assure low droop rates. Since the analog switch always drives into a load at virtual ground, charge injection into the holding capacitor is constant over the entire input voltage range. As a result, the charge offset (pedestal voltage) resulting from this charge injection can be adjusted to zero by use of the offset adjustment capability. The device includes an internal holding capacitor to simplify ease of application; however, provision is also made to add additional external capacitance to improve the output voltage droop rate.