A digital SQUID controller

We describe the performance of an improved DC SQUID controller base upon a PC data acquisition board with a single digital signal processor (DSP). The main DSP algorithm, which handles the flux-locked-loop, is optimally written in assembly language. To improve the performance of the controller, we have added a custom built frequency converter circuit that matches the modulation frequency of the DSP system to that of a commercial SQUID sensor and preamplifier. The noise level of the DC SQUID controller system is comparable with a commercial analog system, similar to4muPhi(0)/rootHz at 100 Hz. The current system could control up to 5 SQUID channels. (C) 2003 Elsevier Science B.V. All rights reserved.