Patent ID: 7142834

Claim:
A noise removing circuit, comprising: a highpass filter for detecting a noise component included in an input signal; an amplifier for amplifying the noise component output from the highpass filter; a time constant circuit for smoothing the amplified noise component with a predetermined time constant and for generating a control voltage that is applied to the amplifier, wherein said time constant circuit comprises: a first capacitor; a charge circuit for charging the first capacitor; a discharge circuit for discharging the first capacitor; and a charge/discharge speed setting unit that causes a difference between a charge speed of the charge circuit and a discharge speed of the discharge circuit; a pulse generating circuit for generating a pulse having a predetermined width at timing when a voltage level of the noise component output from said highpass filter becomes a predetermined reference voltage or higher; an analog delaying circuit for delaying the input signal by a predetermined amount of time, and for outputting the delayed signal; and an outputting circuit for holding the signal output from said analog delaying circuit at immediately preceding timing when the pulse generated by said pulse generating circuit is input, and for outputting the signal output from said analog delaying circuit unchanged in other cases, wherein said analog delaying circuit comprises: a plurality of second capacitors; a plurality of first switches for making said plurality of second capacitors respectively hold the voltage of the input signal in correspondence with supply timing by respectively supplying the input signal to the plurality of second capacitors in a predetermined order at different timing; and a plurality of second switches for extracting the voltage of the input signal respectively held by said plurality of second capacitors before next timing when the voltage is held is reached.