Charge detecting circuit and fingerprint sensor using the same

Details Charge detecting circuit and fingerprint sensor using the same Charge detecting circuit and fingerprint sensor using the same

2005-04-05

2009-08-04

Bella, Matthew C (Department: 2624)

Image analysis

Applications

Personnel identification

Reexamination Certificate

active

07570789

ABSTRACT:
A capacitance detecting circuit detects the variations of capacitances at intersections of a plurality of column lines and a plurality of row lines opposite to the column lines and then converts the variations of capacitances into electrical signals. The capacitance detecting circuit includes a column line driving means that drives the column lines, a comparator that is connected to the row lines to convert charges stored in capacitors formed at the intersections of the driven column lines and the row lines into a measured voltage, and that compares the measured voltage with a predetermined set value to output charging or discharging signals, a constant current source that performs charging or discharging on the charges in response to the charging or discharging signals, and a capacitor that stores charges by means of the charging or discharging current. In the capacitance detecting circuit, a voltage between both ends of the capacitor is output as the electrical signal.

REFERENCES:
patent: 4255057 (1981-03-01), Williams
patent: 5633594 (1997-05-01), Okada
patent: 5778089 (1998-07-01), Borza
patent: 6525547 (2003-02-01), Hayes
patent: 6681033 (2004-01-01), Yano et al.
patent: 2001/0012384 (2001-08-01), Kalnitsky et al.

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