| 摘要 |
PURPOSE:To obtain a circuit whose gain is variable without deteriorating the band by employing a variable resistor using an FET for a source resistance of a differential amplifier. CONSTITUTION:Input signals Vin, the inverse of Vin opposite in phase to each other are amplified by a differential amplifier comprising a transistor Q1(Q2) and outputted from terminals Vout, the inverse of Vout as a voltage drop across a load resistor RL. In this case, the power voltage is given between a terminal VDD and a terminal GND and a constant current source I is given. A gain variable device 4 employing an FET variable resistor in place of a source resistor RS1 is provided to vary the source resistance thereby controlling the gain. Thus, the variable gain amplifier is formed by using one set of differential pairs only.
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