Simulations of signal amplification and oscillations using a SNS junction

A Superconducting - Normal metal - Superconducting junction (SNS junction) may exhibit a Low Voltage Negative Differential Resistance (LVNDR) effect over part of its Current Voltage Characteristic (CVC). As the LVNDR effect is stable against a bias voltage at this CVC range, it should be possible to combine a SNS junction with conventional electronic circuits to obtain electronic devices such as mixers, amplifiers and oscillators. Making use of this remarkable effect, we show tliat an amplifier may be feasible by assembling a simple voltage divider made up of a SNS junction in series witli a resistor. The amplifier circuit includes an adjustable DC voltage supply (the bias voltage) and an AC signal source with a given voltage. The SNS junction is connected in series with a resistor R. Choosing values of the load resistance R approximately equal to the module of the negative differential resistance (dV/dI), at the bias voltage, we may obtain large gains in this amplifier device. In order to get an oscillator, the SNS junction should be connected to a RLC tank circuit with a bias voltage adjusted in the range of the LVNDR region of its CVC. A power output of the order of one microwatt may be easily obtained