Bias Electronics

The Submillimeter Technology Division designs and builds electronics for operation of (cryogenically cooled) mixing devices, such as Superconductor-Insulator-Superconducter (SIS) or Hot-Electron-Bolometer (HEB) mixers, which are regularly used in astronomical heterodyne receivers for the submillimeter regime.

Radioastronomical receivers in the submillimeter regime often use a mixing device as a first stage in their signal chain. The cryogenically cooled mixers need support electronics for operation which e.g. provide low-noise bias voltages to set the correct working point of the devices, apply clean electrical currents to electromagnetic coils to produce a stable magnetic fields etc.

In order to supply such parameters to the cryogenically cooled superconducting sub-mm mixer components, and at the same time to be able to adapt to different receiver needs, a modular design has been developed in our division, which is used throughout all of the coherent receivers designed and operated by the group.

The fundamental part of the design is a microcontroller based mainboard which provides a common electrical interface and is responsible for controlling and monitoring a set of components belonging to a single mixing device. These components are:

• the mixing junction itself
• a cold IF amplifier (HEMT or MMIC)
• a coil for magnetic field to suppress the Josephson oscillations in a SIS junction
• a heater for heating out a junction to eliminate trapped charges

The functionality to bias these components is provided by satellite boards which are plugged into the mainboard as needed. Each mainboard can be configured for different bias components and ranges.

The mainboards communicate over a high level UDP-based communication protocol with a superior control unit (e.g. the main receiver control PC) and can be aggregated according to the number of junctions used.