Patent ID: 6438257
Filing Date: 2002-08-20
Classification: G01R,G06K,G11C

Abstract:
A small capacitance change detection device comprising:a capacitance detection element for detecting a small capacitance change; a signal generation circuit having an output side connected to said capacitance detection element to control predetermined charges; a signal amplification circuit having an input side connected to a connection point between the output side of said signal generation circuit and said capacitance detection element; and an output circuit connected to an output side of said signal amplification circuit, said signal amplification circuit comprising a first transistor having one output terminal connected to the connection portion between the output side of said signal generation circuit and said capacitance detection element, a first voltage source connected to a control terminal of said first transistor, a second voltage source, and a third voltage source, wherein one of said second and third voltage sources is connected to the other output terminal of said first transistor via a first switch, a voltage to be applied from said second voltage source to the other output terminal of said first transistor is set to have a value not less than a value obtained by subtracting a threshold voltage of said first transistor from a voltage of said first voltage source that is applied to the control terminal of said first transistor while a voltage to be applied from said third voltage source to the other output terminal of said first transistor is set to have a value not more than a value obtained by subtracting the threshold voltage of said first transistor from the voltage of said first voltage source that is applied to the control terminal of said first transistor, and said output circuit is connected to a connection point between the other output terminal of said first transistor and said first switch and, after a voltage of one of said second and third voltage sources is applied to the connection point in an ON state of said first switch, receives the voltage at the connection point on the basis of an OFF state of said first switch and charge control by said signal generation circuit after said first switch is turned off.