Cryogenic Differential Amplifier
Cosmic Microwave Technology, Inc. has been developing cryogenic, low noise differential amplifiers primarily for integration with Superconducting Nanowire Single Photon Detectors (SNSPD). The structure of the SNSPD consists of a meandering line embedded on a super-conducting material that is cooled to 1K. The meandering line structure is inherently differential. As a photon strikes the SNSPD, both a positive and negative spike is generated. The differential amplifier allows detection of both pulses.
The low noise of the differential amplifier will result in reducing the timing jitter of the pulses and dramatically improve the performance of the optical links. Higher data rates are achievable resulting in higher resolution images. Currently, two versions of the cryogenic differential amplifiers are available. The AC coupled version is self-biasing and requires only a single supply voltage. This bias arrangement is simple to implement.
A DC coupled version is also available. This version is suited for high data rates since the DC offset caused by AC coupling integratiob is eliminated. This version requires an additional current source for bias of the base junctions of the transistors.