Patent ID: 7173987

Claim:
An analog front end circuit comprising: an analog amplifier which receives an analog signal and the gain of which is controllable; an analog digital converter which digitizes the output of the analog amplifier; and a digital amplifier which multiplies the output of the analog digital converter by an arbitrary value, wherein in a first operation mode, the amplification up to a predetermined gain is performed by said analog amplifier and the amplification thereafter is performed by said digital amplifier, in a second operation mode, the gain of said analog amplifier is fixed and the amplification to a desired gain is performed by said digital amplifier, in a third operation mode, the operation of said analog amplifier is stopped and the amplification for the entire gain is performed only by said digital amplifier, said operation mode is switched over among said first to third operation modes, to perform desired signal processing, a bypass line is provided via changeover switches provided in front of and behind said analog amplifier, and in said third operation mode, by activating the changeover switches, said analog amplifier is bypassed and a power supply of said analog amplifier is cut off.