AN MMIC VARIABLE-GAIN AMPLIFIER USING A CASCODE-CONNECTED FET WITH CONSTANT PHASE DEVIATION

An MMIC variable-gain amplifier, which improves the transmission phase deviation caused by gain control, is presented. At first, it is shown that by controlling both the common-gate FET's gate bias voltage and the common-source FET's gate bias voltage, the transmission phase devi ation caused by gain control of the variable-gain amplifier using a ca scode-connected FET is greatly improved, In this case it is not desira ble to control both of the gate bias voltages independently, because o f the complexity. Thus we propose two simple gate bias voltage control circuits controlling both of the gate bias voltages-in which only one of the two ale bias voltages is controlled independently and the othe r is controlled dependently. Then we apply these circuits to the 1.9-G Hz-band variable-gain amplifier using the cascode-connected FET, One o f the control circuits is the gate bias voltage control circuit using two resistors. It is confirmed that, by applying the newly proposed ci rcuit, phase deviation is suppressed, from between 0 degrees and -30 d egrees to between +3 degrees and -5 degrees, with 25-dB gain control. The other circuit is the gate bias voltage control circuit using the F ET's nonlinear characteristics. It is confirmed that, by applying the newly proposed circuit, phase deviation is suppressed, from between 0 degrees and -44 degrees to between +6 degrees and -3 degrees, with 30- dB gain control. This is a promising technique for reducing the transm ission phase deviation caused by gain control of the amplifiers used i n active phased array antennas.