Practical voltage/current-controlled grounded resistor with dynamic range extension

A novel voltage- or current-controlled grounded resistor is proposed. The circuit makes use of bisection of the drain-to-source voltage of a field effect transistor to produce a practical linear resistor with dynamic range extension. A second generation positive current conveyor is used with three resistors to extend the linearity of the variable resistor, and the resistance can be controlled by a variety of methods. Experimental and PSPICE simulation results, using an AD844 current feedback amplifier and a 2N5485 N-channel JFET, are presented which verify the theoretical derivations. In one experiment, the measured input resistance of the grounded resistor was observed to vary from 1.8 to 18 kOmega or by a factor often.