Patent ID: 7663420
Filing Date: 2010-02-16
Classification: H01L,H03H

Abstract:
1. A MOS attenuator, comprising: a plurality of MOS transistors having a first MOS transistor to N-th (the integer N is larger than 1) MOS transistor being serially connected, the source of the first MOS transistor being set to a first reference potential, the drain of the N-th MOS transistor being set to a second reference potential, and the drain of an I-th MOS transistor being connected to the source of an I+1-th MOS transistor, where I is an integer from 1 to N−1; a current source which is electrically disposed at a connection node between the drain of the N-th MOS transistors and the second reference potential; and a first operational amplifier having a first input terminal, a second input terminal and an output terminal, a third reference potential being supplied to the first input terminal, and the second input terminal being connected with a connection node electrically disposed between the drain of the N-th transistor and the second reference potential, and the output terminal being connected with gates of the MOS transistors; a first attenuator having an input terminal, an output terminal, a plurality of ground MOS transistors and at least one passing MOS transistor, the ground MOS transistors and the passing MOS transistor being disposed between the input terminal and the output terminal of the first attenuator, so that the output terminal of the first operational amplifier is connected with gates of the ground MOS transistors and a control voltage is supplied to a gate of the at least one passing MOS transistor so as to set a characteristic impedance between the input terminal and the output terminal to a predetermined value; a first resistor, electrically disposed between the input terminal of the first attenuator and a fourth reference potential, having an impedance corresponding to the characteristic impedance; a second resistor, electrically disposed between the output terminal of the first attenuator and a fifth reference potential, having an impedance corresponding to the characteristic impedance; a second operational amplifier to generate an amplified output signal in comparison with a voltage at the output terminal of the first attenuator and a predetermined voltage and to output the amplified output signal as the control voltage; and a second attenuator having an input terminal, an output terminal, a plurality of ground MOS transistors and at least one passing MOS transistor, the ground MOS transistors and the passing MOS transistor being disposed between the input terminal and the output terminal of the second attenuator, so that the output terminal of the first operational amplifier is connected with gates of the ground MOS transistors and the control voltage is supplied to a gate of the at least one passing MOS transistor.