Patent ID: 7279970

Claim:
A feedback, having a low-pass filter in an output portion thereof, for feeding a signal from said output portion back thereto, comprising: a first feedback circuit portion for negatively feeding a signal from an input terminal of said low-pass filter back to an inverted input terminal of an operational amplifier; and a second feedback circuit portion for negatively feeding a signal from an output terminal of said low-pass filter back to the inverted input terminal of said operational amplifier, wherein: said second feedback circuit portion is provided with a first feedback operational amplifier and a second feedback operational amplifier, said first feedback operational amplifier has a non-inverted input terminal connected to a predetermined input signal and has an inverted input terminal connected to the output terminal of said low-pass filter, said first feedback operational amplifier has an output terminal connected to the inverted input terminal of said second feedback operational amplifier and the non-inverted input terminal of said operational amplifier, said second feedback operational amplifier has an output terminal connected to the inverted input terminal of said operational amplifier through a resistor, and the output terminal of said first feedback operational amplifier and the non-inverted input terminal of said operational amplifier have a time-constant circuit disposed therebetween.