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It is shown that DC-SQUID read-out electronics can be realized utilizing positive feedback without deteriorating the SQUID noise performance. The required gain rise is achieved by interconnecting the SQUID output and a flux modulation coil via a cooled FET acting as a voltage-controlled resistor; different SQUIDs with different types of FETs have been studied experimentally. Possible ways of adaptively controlling the feedback gain produced by the positive feedback are briefly discussed.
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Seppä et al. (1991) studied this question.
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