RSFQ 1024-bit shift register for acquisition memory

Abstract

Rapid single flux quantum (RSFQ) 512-bit and 1024-bit shift registers have been demonstrated. These are the longest superconducting shift registers reported to date, employing 1045 and 2069 Josephson junctions, respectively. The circuit functionality has been confirmed with dc bias margins of +or-23% and +or-14% for the 512-bit and the 1024-bit shift registers, respectively. The 512-bit shift register has been tested to 20 GHz and 1024-bit register to 19 GHz using an external clock trigger with relative delay measurements at single and double SFQ clock frequencies. The shift registers with the same design have been used for successful implementation of the acquisition shift register (ASR) memory for the projected transient digitizer. These shift registers have the ability to acquire data at high speeds (gigahertz range), statically hold the acquired data, and then read-out the data into conventional room-temperature electronics at low speeds (megahertz range). A 32-bit ASR has been tested up to 18 GHz (the limit of our test setup), and a 1024-bit ASR-up to 16 GHz of acquisition rates, both at 33 MHz read-out frequency. Total power dissipation is about 1 mW for the 1024-bit circuit. The chips are fabricated using Hypres' Nb/AlO/sub x//Nb process with a junction critical current density of 1.0 kA/cm/sup 2/.