Parametric amplifier with thermo-electric refrigeration

It is now well known that the noise figure of the variable capacitance parametric amplifier can be greatly improved by refrigerating the diode to liquid nitrogen temperatures. To make this into a practical device, the major problem is the cryogenic system. It is much larger than the amplifier itself and requires considerable maintenance. A thermo-electric refrigerator is a very useful device for this application, because it is compact and operates with little attention. A thermo-electric refrigerator can easily be built into the amplifier without significantly increasing its mechanical dimensions. The only disadvantage of this device is that the lowest temperature achievable by a two stage refrigetor is around 215° K.