We analyzed theoretically and simulated 4-bits RSFQ logic based Pseudo Random Generators (PRG). These circuits were fabricated in IRE RAN using niobium technology. Before testing the PRG, we had experimentally investigated an XOR cell and a shift register with parallel outputs that had been used as compound parts of the PRG Experimentally measured margins for DC power supply voltage for the PRG with a serial output, the XOR cell and shift register were 10%, 15%, and 15% correspondingly. In this paper we are going to discuss the possible applications of PRG in RSFQ testing circuits and as a source of quasi-'white" digital noise.
ITRODUCTION
In different fields of engineering such as noise measurements, computer testing and others, generation of random signals is an important task. There exist a lot of methods to generate random signals using digital equipment . All of them consider a Pseudo Random Generator (PRG) that creates the desired random telegraph signal, as a main part. PRG has a wide frequency range, the upper boundry of this range is of great importance in computer testing and code-decode tasks. It is especially important in testing superconductor digital circuits with extremely high operating frequency, e.g., RSFQ logic/memory cells . During the last five years the RSFQ logic family has made remarkable progress. It has become obvious that now the digital circuits based on RSFQ logic elements are the constituent part of modern superconducting electronics. Multiple RSFQ devices have been suggested, analyzed theoretically, and demonstrated experimentally up to the present date . Traditionally low-speed methods, when all inputs are fed manually using external RS flip-flops with microsecond periods and delays, have been applied for testing RSFQ devices . As soon as a typical RSFQ unit can operate theoretically at very high frequencies (more than 500 GHz), so high-speed testing is necessary to expose the advantages of this family. Unfortunately, external semiconductor sources cannot provide and handle such high-frequency signals. In this paper we suggest a RSFQ PRG which, being built in a testing RSFQ circuit, can generate testing sequences at a required rate. Also we discuss the possibility of using PRG as a source of"quasiwhite" digital noise to calibrate noise detectors and similar devices.
RSFQ PSEUDO RANDOM GENERATOR DESIGN
The easiest RSFQ PRG (Fig. ) consists of a shift register, a mixing element (typically a two-input XOR element) and an initializing cell (DC/SFQ converter [3], for example). The inputs of the XOR element are connected to the last and any (but not arbitrary) cells of the shift register whereas the output is connected to the first cell. The number of bits of the shift register N determines the correct way of a connecting the XOR element to the register (the number of the second source cell Ni) and the longest period ]max of a pseudo-random sequence generated by the PRG: _T,,,~ = 2 ~ -1. The value of N i may be calculated using the theory of non-reducible primitive binary polynomes (see Table ). Note that a PRG may be either serial