Voltage-Controlled Amplifier

  
The CA3080 can be used as a gain controlling device. The input signal is attenuated by R1/R2 so that a 20-mVpp
Voltage-Controlled Amplifier - schematic

signal is applied to the input terminals. If this voltage is much larger, significant distortion will occur at the output. In fact, this distortion is put to good use in the triangle-to-sine wave converter. The gain of the circuit is controlled by the magnitude of the current IABC. This current flows into the CA3080 at pin 5, which is held at one diode voltage drop above the - VCc rail· The gain of the CA3080 is " "linearly" proportional to the magnitude of the IABC current over a range of 0.1 to 1 mA. Thus, by controlling IABC, you can control the signal level at the output. The output is a current output, which has to be "dumped" into a resistive load (R5) to produce a voltage output. The output impedance at IC1 pin 6 is 10 kfi (R5), but this is "unloaded" by the voltage follower (IC2) to produce a low output impedance. The circuit around IC3 is a precision voltage-to-current converter and this can be used to generate IABC. When Vm (control) is positive, it linearly controls the gain of the circuit. When it is negative, IABC is zero and so the gain is zero.




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