Low-Noise, Direct-Current, Squid Amplifier with Simplified Readout Electronics

Because of their low noise and enormous bandwidth, dc Superconducting Quantum Interference Devices (SQUID)s are very attractive as amplifiers for many applications. Conventional SQUID amplifiers are often not suitable for these applications, because the readout electronics employ flux modulation which imposes a severe bandwidth limitation and increases their complexity. For applications in space, this significantly increases the cost of preparing flight-qualified electronics. If the SQUID is not properly designed and damped, parasitic resonances are introduced, complicating the operation of the SQUID and leading to excess noise which degrades performance. We propose to develop a low-noise, two-stage SQUID amplifier with very simple electronics and appropriate packaging that is ideally suited for cryogenic detector readout applications in space. The amplifier consists of a single, low-noise SQUID input stage, followed by a coherently modulated, series-connected SQUID array output stage. A proven design optimization procedure is employed to ensure proper treatment of the parasitic resonances. Properly designed, the output noise is dominated by the amplified noise of the input SQUID and is sufficiently high to allow direct connection to a room-temperature preamplifier. Additional electronics are not required, and the high bandwidth and dynamic range are preserved.