A LOW-NOISE, 2-STAGE DC SQUID AMPLIFIER WITH HIGH-BANDWIDTH AND DYNAMIC-RANGE

We describe a low-noise, two-stage de Superconducting QUantum Interfer ence Device (SQUID) amplifier that is designed for applications requir ing high bandwidth and dynamic range. The output signal of a low-noise SQUID in the input stage coherently modulates a series array of ident ical SQUIDs in the output stage via a common modulation line. The inpu t stage is designed so its output signal does not produce multiple mod ulation periods in the output stage. The output stage is designed to h ave sufficient gain so the output noise is dominated by the amplified noise of the input SQUID and exceeds the noise of a preamplifier in th e room temperature readout electronics. The SQUID amplifier may theref ore be operated without flux modulation or any impedance matching netw ork, resulting in a large dynamic range and high bandwidth.