Mediatek Singapore Pte. Ltd.

Ten Voon Wong

Rawinder Dharmalinggam

Wee Liang Lien

A variable gain amplifying circuit comprises two stages, a first stage and a second stage with a common voltage-to-current converter. Each stage comprises two BJTs, two voltage controlled current sources, a variable resistor with a variable resistance, and the common voltage-to-current converter. The two BJTs construct a differential amplifier for amplifying a pair of differential signals. The variable resistor with the variable resistance is connected between the emitters of the two BJTs wherein the variable resistance of the variable resistor is represented as R. The variable resistance Ris controlled by a control voltage V. The two voltage controlled current sources are respectively connected between the corresponding emitter of BJTs and ground. The currents respectively through the voltage controlled current sources are equal to each other and represented as I. The current Iis controlled by the common voltage-to-current converter according the control voltage V. The variable resistance Rand the current Iof the voltage controlled current sources can be varied simultaneously by the control voltage Vso as to rapidly adjust the gain of the variable gain amplifying circuit.

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Oakville, Canada

Ten Voon Wong