A 1-MHz low noise preamplifier based on double relaxation oscillation SQUIDs

A low noise and wideband preamplifier based on Double Relaxation Oscillation Superconducting Quantum Interference Devices (DROSs) has been realized. A major advantage of a DROS is that it can be operated in a simple flux modulation. So far, biomagnetic measurements performed in our group required only a limited bandwidth smaller than 100 kHz. Other applications, like for instance readout of radiation and particle detectors, demand a larger bandwidth. In this paper, we will discuss our efforts aimed at increasing the operational bandwidth of a DROS in flux locked loop. Presently, a flux locked loop scheme with a -3 dB bandwidth of 1.45 MHz has been built. With this system a white flux noise of 8 /spl mu//spl Phi//sub 0///spl radic/Hz was measured with a 1/f-corner frequency of 10 Hz. The slew rate was 2.5/spl middot/10/sup 5/ /spl Phi//sub 0//s. With the mutual input inductance of 6.7 nH, an input current noise of the preamplifier of 2.5 pA//spl radic/Hz was found and a current slew rate of 80 mA/s. We will discuss the suitability of our DROS-based preamplifier for readout of cryogenic particle detectors based on superconducting tunnel junctions.