Superregenerative circuits using tunnel diodes

Abstract

CONSIDERABLE DIFFICULTY has been experienced by tunneldiode circuit designers in attempting to bias the tunnel diode in the negative-resistance region and still maintaining a reasonable degree of stability. In the superregenerative circuit we may bias the tunnel diode outside of the negative resistance region, as shown in Figure 1, and periodically permit the operating point to be driven into the negative resistance region. The initial operating point may be in the forward or reverse voltage region depending upon the quench magnitude. During the excursion into the negative resistance region, provided that the net circuit resistance during this time is negative, the circuit will become oscillatory and will build up at a rate which is a function of the circuit parameters. If a small signal is injected into the resonant circuit, the rate of oscillation buildup will be a function of the input signal magnitude. Therefore, it is desired that the natural rate of oscillator voltage buildup be relatively slow. The requirements for various modes of oscillation (i.e., sinusoidal, relaxation) for a device having a negative resistance characteristic have been previously derived’. This analysis has been extended to include the tunnel diode by assuming a cubic relationship between diode current and voltage. It is shown that the voltage-time relationship for a negative resistance device, as shown in Figure 2, is given by the differential equation shown therein. RN is the value of the negative resistance at the dc operating point and R includes the tank loss and load resistance. The character of the buildup of the oscillator voltage is highly dependent upon the magnitude of e and it may be shown’ that for e 5 1, the buildup is of a relaxation type while for e 5 0.2 the voltage is sinusoidal with a slow buildup.