Patent ID: 6900752
Filing Date: 2005-05-31
Classification: H03M

Abstract:
1. A variable resistance device comprising: a first variable resistance circuit including n resistors connected in series forming a first series-resistor circuit and analog switches connected between one terminal of the series-resistor circuit and respective nodes of the resistors of the series-resistor circuit, n being an integer of 2 or more, the analog switches being on/off controlled by an output signal of a counter to stepwise change a resistance value of the first variable resistance circuit; a second variable resistance circuit one terminal of which is connected to the one terminal of the first series-resistor circuit of the first variable resistance circuit, the second variable resistance circuit including a second series-resistor circuit of a first resistor and a second resistor which have a predetermined resistance ratio therebetween, one terminal of the first resistor being connected to one terminal of the second resistor, the other terminal of the first resistor being connected to the one terminal of the series-resistor circuit of the first variable resistance circuit, a third series-resistor circuit of a plurality of resistors, one terminal of third series-resistor circuit being connected to the other terminal of the second resistor, a plurality of analog switches connected between the other terminal of the first resistor and nodes of the respective resistors of the third series-resistor circuit, an analog switch connected between the other terminal of the third series-resistor circuit and a node of the first resistor and the second resistor and controlled by an output signal of a counter, an analog switch connected between a node of resistors of the third series-resistor circuit and the node of the first resistor and the second resistor and controlled by an output signal of a counter, and a short-circuiting analog switch connected between the other terminal of series-resistor circuit of the first variable resistance circuit and the other terminal of the second resistor of the second variable resistance circuit and controlled by an output signal of a counter to make a short-circuit therebetween.