3.69 GHz single flux quantum pseudorandom bit sequence generator fabricated with Nb/AlO/sub x//Nb

A 4 bit 15 sequence SFQ (Single Flux Quantum) pseudorandom bit sequence generator was built with an eight-level Nb/AlO/sub x//Nb Josephson junction integrated circuit process. An SFQ circuit was built into the code generator to enable a rapid restart. The test results showed that the circuit operated correctly at the seed of 3.69 GHz. The XNOR gate and shift register worked correctly at 5 GHz. However, the back delay was longer than 200 psec and the generator acted as a 5 bit 21 sequence code generator at this frequency. At 200 MHz, the code generator was operated continuously to observe its stability. Over the course of two and one half hours, the circuit made only five code errors, indicating a bit error rate of 3/spl times/10/sup -12/. At 2 GHz we collected 10 million samples on the 4023rd bit of the sequence. No wrong signal values were observed, indicating the bit error rate is less than 5/spl times/10/sup -11/ at this frequency.