A simple SQUID system with one operational amplifier as readout electronics

We describe a dc Superconducting Quantum Interference Device (SQUID) readout electronics in Flux Locked Loop (FLL) mode without integrator and with only one operational amplifier, which is called Single Chip Readout Electronics (SCRE). A weakly damped niobium-SQUID magnetometer with a large flux-to-voltage transfer coefficient of about ∂V/∂Φ ≈ 380 μV/Φ₀ and SCRE results in a very simple SQUID system. We characterize the system and demonstrate its applicability to Magnetocardiography (MCG) and measurements using the Transient ElectroMagnetic (TEM) method. SCRE not only simplifies the readout scheme, but also improves the system stability, the bandwidth and the slew rate. The difference between SCRE and a conventional readout scheme (preamplifier + amplifier + integrator) is also discussed. (paper)