Op amp linearizes response of FET VCA

摘要

Fets bind common use in VCAs (voltage-controlled ampli-fiers) and attenuators, in which the FET serves as a variable resistance. A control voltage applied to the gate sets the channel resistance and overall circuit gain. You frequently need to select individual FETs because of wide spreads in FET characteristics. The circuit in Figure 1 uses a master-slave servo technique with a matched-FET pair to implement voltage-controlled variable gain. This gain is a linear function of the applied control voltage, V_c.