Numerical analysis of the smart DROS

A digital superconducting quantum interference device (SQUID) has the potential for a very large dynamic range and a very high slew rate. Our concept of the digital SQUID consists of a double relaxation oscillation SQUID (DROS) with the complete flux locked loop (FLL) electronics on one single chip. The key element of the FLL circuitry is a superconducting up-down counter, which supplies the feedback flux to the DROS. In this paper we will concentrate on the numerical simulations of our new 100 MHz smart DROS. In this new design, the quantization unit of the feedback flux, δΦ_fb=52 mΦ₀, was optimized with respect to the flux noise of the DROS. By doing so, the flux slew rate was maximized without compromising the sensitivity. The optimization resulted in a maximum flux slew rate of δΦ_sig/δt=5×10⁶Φ₀/s.