High speed testing of a four-bit RSFQ decimation digital filter
We have developed a high speed test scheme for RSFQ circuits, in order to measure the maximum clock frequency of a four-bit RSFQ decimation digital filter (simulated to be 11 GHz). Our high speed test requires only a low speed interface and standard low-cost measurement equipment. Three auxiliary test units built of simple RSFQ circuits are used. A circular JTL structure generates an on-chip high speed clock with frequency adjustable from 4 to 16 GHz. A pseudo-random number generator with period 64 clock cycles provides parallel input to the filter. Finally, 12 four-bit acquisition shift registers collect output data. We have integrated all the above units on a single chip. The chip is initialized at low speed, run at high speed, and read out at low speed. Our testing scheme is superior to previously reported high-speed tests in the area of the added circuitry, in the requirements on high-speed input/output, in control, and in the parameters of the measurement equipment. The scheme can be easily adapted to test various RSFQ circuits.