Compact readout electronics for 62-channel DROS magnetocardiogram system

Compact and low-cost SQUID electronics to operate double relaxation oscillation SQUIDs (DROSs) has been constructed for detecting magnetocardiogram (MCG) fields. SQUID electronics consists of low-noise preamplifier with a white noise of 0.6 nV//spl radic/Hz, flux-locked loop (FLL) circuit with auto-reset, and interface circuit to control FLL using 3 digital lines from a computer. The automatic control software adjusts SQUID parameters to the optimum operating condition within 15 seconds for 62 channels. Outputs of FLL circuits are passed through the hardware filter box to the 64-channel data acquisition board. Each SQUID electronics for FLL and digital control is built together on a printed circuit board of 45 mm /spl times/ 95 mm. When SQUID electronics is connected to DROS gradiometer with typical flux-to-voltage transfers of 1 mV//spl Phi//sub o/, the noise contribution of FLL circuit is about 0.6 /spl mu//spl Phi//sub o///spl radic/Hz or 0.6 fT//spl radic/Hz at 100 Hz, low enough to measure MCG fields.