Multicrossover Cryotron—a High Gain Single Stage Amplifier

Present high gain cryotron amplifiers use dc biased cascaded crossed film cryotrons, and cannot be operated below 1 kHz because of low frequency noise. It is shown that in situations where minimum input inductance is not required, a much simpler circuit, using a crossed film cryotron with many crossovers, can be used as a single stage high gain amplifier. It is found that, if gate bias is applied in the form of pulses, helium bubble formation, which is the cause of low frequency noise, is inhibited. Also the chopping action of the gate pulse allows the amplification of dc signals. The multicrossover cryotrons described have 512 crossovers and exhibit bandwidths of 1 MHz and transimpedances of up to 10 mV/mA. It has been possible to explain their nonmonotonic gain‐temperature dependence in terms of penetration depth and thermal propagation effects.