Buffer Amplifier with Femtofarad Input Capacity Using Operational Amplifiers

Abstract
A unity-gain buffer amplifier with an input capacity below 0.01 pF and an input resistance above 10 12 Ω is described. Low input capacity is achieved without the necessity of feedback adjustments by bootstrapping the entire input stage, including power sources and shielding. The amplifier is of simple design and is based around commercially available operational amplifiers.