An ultrasensitive linear cryotron amplifier

This report shows that crossed film cryotrons can be cascaded to form high-gain, high-sensitivity amplifiers if negative feedback is applied to counteract a large low-frequency noise component. The design of cryotron feedback amplifiers is analyzed, and several practical amplifier circuits are described. One of these has an upper cutoff frequency of 1.7 Mc per stage, and another can detect 5×10^-11v at 1000 cps with a 45 kc bandwidth. These figures are believed to represent an order of magnitude improvement in speed and sensitivity over previous low-noise amplifiers designed to sense low impedance cryogenic sources. The report also includes new data on the effect of control width on crossed film cryotron characteristics, and describes a method of obtaining an arbitrarily large output voltage from a cryotron circuit, without any sacrifice in bandwidth.