Browse Prior Art Database

DC ELECTROMETER STABILIZED CIRCUIT

IP.com Disclosure Number: IPCOM000023038D
Original Publication Date: 1976-Jul-31
Included in the Prior Art Database: 2004-Mar-27
Document File: 2 page(s) / 302K

Publishing Venue

Xerox Disclosure Journal

Abstract

The figure shows an electrometer amplifier 10 designed for the indirect measurement of a surface electrostatic poten~ tiaL The potential on a surface distributes itself electrostati~ cally between the probe-to-~surfacecapacitance and a fixed capacitor 12 at the input of the electrometer l0~

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Page 1 of 2

XEROX DISCLOSURE JOURNAL

     ELECTROMETER STABILIZED
C IRCUIT
Rudolph Vargas, Jr~

Proposed Classification
U0S~ CL 324/72
Int~. C1~ GOir 31/02

The figure shows an electrometer amplifier 10 designed for
the indirect measurement of a surface electrostatic poten~
tiaL

The potential on a surface distributes itself electrostati~
cally between the probe-to-~surfacecapacitance and a fixed
capacitor 12 at the input of the electrometer l0~

The potential on the capacitor 12 is monitored by one~half
of a dual differential matched field effect transistor
(FET) 14 (MOSFET or JFET, only the JFET configuration being
shown), operating in the source follower configurations
The output of the source follower (source outputs 16 and
18) drives a differential bipolar transistor pair 20 (or
differential FET pair), operating as a differential common
emitter (or common source) amplifier, providing the open
loop gain of the circuit~

Collector output 22 of the transistor amplifier 20 is fed
back through a gain determining resistive divider comprising
resistors 24 and 26 to the gate 28 of the alternate source
FET, The circuit ioop gain forces the gate voltage of the
alternate FET to track the voltage ~ applied to the gate
30 of the input FET, preserving their balanced operation~

+ 7V

7V

volume 1 Number 7 July 1976 43

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Page 2 of 2

D.C. ELECTROMETER STABILIZED CIRCUIT (Cont~d)

The result is optimum signal tracking with minimized thermal
unbalance. An indication of...