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Capacitor Characterization Device

IP.com Disclosure Number: IPCOM000081185D
Original Publication Date: 1974-Apr-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Davis, J: AUTHOR [+2]

Abstract

Presently available capacitance testing devices are not readily used for determining capacitance characteristics, the capacity-voltage (C-V) relationship and selected parameters along the C-V curve for variable-capacitance units such as metal-oxide semiconductor (MOS) capacitors.

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Capacitor Characterization Device

Presently available capacitance testing devices are not readily used for determining capacitance characteristics, the capacity-voltage (C-V) relationship and selected parameters along the C-V curve for variable-capacitance units such as metal-oxide semiconductor (MOS) capacitors.

As shown in the diagram, a capacitor 1 to be tested is connected to a capacitance bridge tester 2 which has a ramp voltage input 3 to be applied to the capacitor, and an analog output 4 indicating the measured capacitance. As indicated in the Fig. 2 graph, capacitors of the MOS type have a maximum capacitance at low voltage, will have a smooth decrease of capacity as the voltage across it increases and will level off at a minimum capacitance for higher voltages.

A start test signal from a controlling processor system will be applied to an analog-to-digital (A-to-D) converter 5, to hold the digital output lines 6 at the digital value of the initial capacitance C max. The start signal is also applied to a single-shot delay circuit 7, which starts the ramp generator 8 to gradually increase the test voltage on line 3 after C max has been measured.

The measured C max on lines 6 is reconverted in digital-to-analog circuit 9 to an analog voltage on line 10. The potentiometer 11 is set to a factor representing the ratio of a capacitance C fb (flat band) to C max, and the output of potentiometer 11 is applied over line 12 to a comparator 13, which also receives the measured capacitance analog voltage on output 4. When the measured capacity has decreased to the value set on line 12, comparator 13 will put a signal on line 14 to fire a single-shot 15, which will energize sample and hold circu...