AM INTERMEDIATE FREQUENCY VARIABLE GAIN AMPLIFIER CIRCUIT, VARIABLE GAIN AMPLIFIER CIRCUIT, AND SEMICONDUCTOR INTEGRATED CIRCUIT THEREOF

摘要

PROBLEM TO BE SOLVED: To provide a variable gain amplifier circuit which is used with a low power source voltage, generating little noise inside the circuit. SOLUTION: A MOS transistor 35 is connected between the sources of MOS transistors 33, 34 constituting a differential amplifier circuit. A DC bias voltage for operating the MOS transistor 35 in a nonsaturation area is applied onto the gate of the MOS transistor 35. When the output voltage of the variable gain amplifier circuit 30 is increased, a control voltage to reduce resistance between the source and drain of the MOS transistor 35 is given, so as to reduce the gain of an AM intermediate frequency variable gain amplifier circuit 30. COPYRIGHT: (C)2005,JPO&NCIPI