Patent ID: 7138869

Claim:
An amplifier circuit, comprising: an operational amplifier having a first input terminal, a second input terminal, and an output terminal; a capacitive device coupled between the second input terminal and an input voltage; and a resistor network comprising a plurality of stages connected serially, coupled between the second input terminal and the output terminal, wherein each stage of the resistor network comprises: an input node; an output node; a first resistor coupled between the input node and a common node; and a second resistor coupled between the input node and the output node; wherein an input and an output of the resistor network are the input node of the first stage and the output node of the last stage of the resistor network, respectively; wherein a current of the input of the resistor network is larger than that of the output of the resistor network such that the amplifier circuit has a large-resistance capacitive time constant.