A low input capacitance voltage follower in a compatible silicon-gate MOS-bipolar technology

Using a compatible silicon-gate p-MOS-bipolar technology (SIGBIP), a voltage follower is described with protected MOSFET input stage featuring less than 1-pA input current, less than 0.1-pF input capacitance, 10-MHz bandwidth, 20-/spl mu/V p-t-p noise from 1 Hz to 100 kHz. Offset drift is less than 30 /spl mu/V//spl deg/C. The circuit is based on a new very high-gain differential stage which allows full bootstrapping of all its input capacitances. The circuit measures only 0.9 mm/SUP 2/ and is mounted in a 4-pin TO-18 package. The circuit can successfully be used for charge measurements, and especially for wide-band measurements from very high impedance sources (>10 M/spl Omega/) as occurring in bioelectronics, biochemistry, etc.