Wideband cryogenic amplifier for a superconducting nanowire single-photon detector

We present a low-power inductorless wideband differential cryogenic amplifier using a 0.13-µm SiGe BiCMOS process for a superconducting nanowire single-photon detector (SNSPD). With a shunt-shunt feedback and capacitive coupling structure, theoretical analysis and simulations were undertaken, highlighting the relationship of the amplifier gain with the tunable design parameters of the circuit. In this way, the design and optimization flexibility can be increased, and a required gain can be achieved even without an accurate cryogenic device model. To realize a flat terminal impedance over the frequency of interest, an RC shunt compensation structure was employed, improving the amplifier’s closed-loop stability and suppressing the amplifier overshoot. The S-parameters and transient performance were measured at room temperature (300 K) and cryogenic temperature (4.2 K). With good input and output matching, the measurement results showed that the amplifier achieved a 21-dB gain with a 3-dB bandwidth of 1.13 GHz at 300 K. At 4.2 K, the gain of the amplifier can be tuned from 15 to 24 dB, achieving a 3-dB bandwidth spanning from 120 kHz to 1.3 GHz and consuming only 3.1 mW. Excluding the chip pads, the amplifier chip core area was only about 0.073 mm2.