DC-SQUID electronics based on the noise cancellation scheme

Abstract

We have constructed a compact dc SQUID electronics unit, in which the noise of the roomtemperature amplifier is measured by the SQUID and cancelled out. This makes it unnecessary to use a transformer and a modulation scheme to achieve noise matching between the SQUID and the amplifier. The electronics unit contains a P13~2-controller and it has demonstrated a bandwidth of 100 kHz, a 1.2 p @~/ & white noise level and a l/f noise corner of 0.3 Hz in a flux-locked loop mode. The design criteria for the noise-cancelled electronics are discussed, including the problem of exess noise.

Practical dc SQUID system: Devices and electronics

“…Generally, the system noise depends on SQUID intrinsic noise, on the SQUID's flux-to-voltage transfer coefficient @V/@U, and on the preamplifier noise, which includes two sources: a voltage source V n and a current source I n . For both voltage-and current-bias mode, different voltage feedback circuits (VFC), such as additional positive feedback (APF) [2], noise cancelation (NC) [3] and SQUID bootstrap circuit (SBC) [4], have been introduced to increase @V/@U. Another way is to employ a weakly damped SQUID with large StewartMcCumber parameter b c , which exhibits a large @V/@U of several hundred lV/U 0 [5].…”

Novel Superconducting Quantum Interference Device Bootstrap Circuit and Its Application in Biomagnetism

“…It enhances the flux-tovoltage transfer coefficient to suppress the flux noise contribution of the preamplifier by setting a working point on the steep slope of a strongly asymmetric V-Φ characteristic. The other one, called noise cancellation (NC), is proposed by Seppä et al and is operated in voltage bias mode [4]. The NC increases the dynamic resistance of NC circuit, thus reducing the preamplifier noise.…”

Simplified analysis of direct SQUID readout schemes

“…It has beco me more and more popular in the past decade, stimulated in part by the need of higher bandwidth and slew rate, e.g., for the readout of cryogenic detectors. Various methods have been developed to suppress the effect of amplifier noise when using direct readout [4][5][6][7][8][9][10][11].…”