Browse Prior Art Database

Charge Sensing Using Bridge Networks

IP.com Disclosure Number: IPCOM000076664D
Original Publication Date: 1972-Apr-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 22K

Publishing Venue

IBM

Related People

Lee, HS: AUTHOR

Abstract

This is a capacitor sensor for measuring the presence of minute quantities of charge in localized regions in a semiconductor body. The sensor uses a capacitor bridge scheme for detecting the small charge changes to be expected from charge-coupled devices. The use of the bridge network allows more noise tolerance and sensing of smaller signals.

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Charge Sensing Using Bridge Networks

This is a capacitor sensor for measuring the presence of minute quantities of charge in localized regions in a semiconductor body. The sensor uses a capacitor bridge scheme for detecting the small charge changes to be expected from charge-coupled devices. The use of the bridge network allows more noise tolerance and sensing of smaller signals.

The circuit comprises an AC generator 10 coupled across a capacitor bridge 11, containing capacitors C1, C2, C3 and C4. Also, coupled to the capacitor bridge is an field-effect transistor (FET) detector or comparator circuit 12. Capacitor C4 of the circuit is one of the stages of a charge-coupled device. It is arranged with the other capacitors C1, C2 and C3 such that the presence of a packet of charges representing a bit "1", or the absence of such a packet of charges representing bit "0" within capacitor C4 can be detected, by the difference in the voltage outputs from the bridge network. When the bridge 11 is balanced the outputs coupled into the comparator circuit 12 are both at the same potential, but when the magnitude of the capacitor C4 is changed by having charges introduced into it; i.e., a 1 or charges taken out of it; 0, the bridge becomes unbalanced. Because C4 is thus variable, amplification of the charge is realized and a voltage proportional to the degree of unbalance is fed to comparator 12. Since the magnitude of the differential capacitance of the capacitor C4 is a fun...