FIG. 15 shows an embodiment method and apparatus to provide feedback that lowers nonlinear resistor distortion of the drain to source resistance of the FET (e.g., Q2B) via amplifiers with a net gain of 0.5 from the drain to gate of the FET. FIG. 15 also prevents the control voltage from VR1 from leaking or passing to the output terminal Vout. An input signal Vin is coupled via a resistor Rs and the drain to source resistance of Q2B form a voltage divider in parallel with R1. R1 may be removed optionally.
In the circuit shown in FIG. 15, the circuit provides a smaller control voltage from VR1 compared to circuit such as shown in FIGS. 3, 4, 5, and 6 that attenuates (via the feedback network) the control voltage by 50% to the gate of the FET. Because of this 50% attenuation of the control voltage to the gate terminal, the circuits shown in FIG. 3, 4, 5, and or 6 for example require twice the voltage than control voltages for FIGS. 1 and 2 for the same attenuation range. The amplifier circuit in FIG. 15 includes an amplifier U1B that allows the control voltage from VR1 to be transferred without attenuation to the gate of the FET.
