Constant impedance sampling switch for an analog to digital converter

TLDR: In this paper, the authors propose a sampling switch with a single metal oxide semiconductor (MOS) transistor to selectively couple the input signal to a sampling circuit, where the potential difference between the signal being sampled and the gate potential of the transistor remains substantially constant over a relatively wide range of amplitudes for the analog input signal.

Abstract: A constant impedance sampling switch suitable for a high-frequency analog-to-digital converter, presents a substantially constant impedance to the input signal regardless of the instantaneous level of the input signal. The exemplary sampling switch employs a single metal oxide semiconductor (MOS) transistor to selectively couple the input signal to a sampling circuit. The gate signal for this transistor is generated by circuitry which is disconnected from the gate of the transistor while the transistor is in an non-conductive state. During a sampling interval, the gate signal is boot-strapped by the instantaneous potential of the input signal to render the transistor conductive. Accordingly, the potential difference between the signal being sampled and the gate potential of the transistor remains substantially constant over a relatively wide range of amplitudes for the analog input signal.