Front-end control electronics

Mixer-control

The mixer control provides a stable bias-circuit (most critical for reliable operation) and a protection circuit for the mixers, a magnet current for suppressing the DC-Josephson current at the superconductive mixer junction, and a heater current to remove trapped magnetic flux quanta from the device, if necessary. In total there are 16 individual units available, one for each mixer (plus two spares). The complete system can be controlled remotely, but also manually if desired. To optimize the mixer tuning, IV-curves and also the conversion curves of the mixers can be displayed online.

Local Oscillator control

The concept of using a high power W-band signal fed into cascaded frequency multiplier diodes to generate the submm local oscillator signal requires that these devices are operated at their limit. The voltage swing induced in the 1st multiplier stage easily can be large enough to damage or even destroy the device, if the input power is too high or the device is not operated at the right bias point. Therefore the low noise DC supply voltages of the local oscillator chains are generated in a dedicated control unit, a development copied from the Herschel/HIFI program. Many safety features have been implemented in this unit to avoid that the LO chains can be damaged by wrong handling or main supply failure. The internal microprocessor manages the switch-on and switch-off procedure of the chain components in a safe order. Even in case of a failure of the main, the unit is capable to switch-off the active chain in the right (safe) order. Hardware current limits are implemented to avoid excessive forward or reverse currents of the multipliers. Programmable current limits for the amplifier drain stages decrease the likeliness of damaging the amplifier by wrong biasing of the stages.