Complementary Paired G⁴FETs as Voltage-Controlled NDR Device

NASA’s Jet Propulsion Laboratory

It is possible to synthesize a voltage-controlled negative-differential-resistance (NDR) device or circuit by use of a pair of complementary G⁴FETs (four-gate field-effect transistors). [For more information about G⁴FETs, please see "G⁴FET Implementations of Some Logic Circuits" (NPO-44007).] As shown in Figure 1, the present voltage-controlled NDR device or circuit is an updated version of a prior NDR device or circuit, known as a lambda diode, that contains a pair of complementary junction field-effect transistors (JFETs). (The lambda diode is so named because its current-versus-voltage plot bears some resemblance to an uppercase lambda.) The present version can be derived from the prior version by substituting G⁴FETs for the JFETs and connecting both JFET gates of each G⁴FET together. The front gate terminals of the G⁴FETs constitute additional terminals (that is, terminals not available in the older JFET version) to which one can apply control voltages V_N and V_P.

Figure 1. A Lambda Diode is a negative-resistance circuit or device, previously made from JFETs, and now made from G⁴FETs.

Circuits in which NDR devices have been used include (1) Schmitt triggers and (2) oscillators containing inductance/ capacitance (LC) resonant circuits. Figure 2 depicts such circuits containing G⁴FET NDR devices like that of Figure 1. In the Schmitt trigger shown here, the G⁴FET NDR is loaded with an ordinary inversion-mode, p-channel, metal oxide/semiconductor field-effect transistor (inversion-mode PMOSFET), the V_N terminal of the G⁴FET NDR device is used as an input terminal, and the input terminals of the PMOSFET and the G⁴FET NDR device are connected. V_P can be used as an extra control voltage (that is, a control voltage not available in a typical prior Schmitt trigger) for adjusting the pinch-off voltage of the p-channel G⁴FET and thereby adjusting the trigger- voltage window.

Figure 2. This LC Oscillator and Schmitt Trigger are examples of enhanced NDR circuits that can be made by use of G⁴FETs.

In the oscillator, a G⁴FET NDR device is loaded with a conventional LC tank circuit. As in other LC NDR oscillators, oscillation occurs because the NDR counteracts the resistance in the tank circuit. The advantage of this G⁴FET NDR LC oscillator over a conventional LC NDR oscillator is that one can apply a time-varying signal to one of the extra control input terminals (V_N or V_P) to modulate the conductance of the NDR device and thereby amplitude-modulate the output signal.

This work was done by Mohammad Mojarradi of Caltech; Suheng Chen, Ben Blalock, Chuck Britton, Ben Prothro, and James Vandersand of the University of Tennessee; Ron Schrimph of Vanderbilt University; and Sorin Cristoloveanu, Kerem Akarvardar, and P. Gentil of Grenoble University for NASA’s Jet Propulsion Laboratory.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to: