Investigation of the parasitic coupling effects in densely packaged RSFQ digital circuits

The Rapid Single Flux Quantum (RSFQ) technique is regarded as one of the most promising electronics due to its extremely high operating speed and low power consumption. Middle-scale RSFQ applications operating at multigigahertz frequency have recently been reported on. At such high operating frequencies, the on-chip interconnects start to play a limiting role for the performance of the densely packaged digital circuits. Our previous studies have theoretically investigated the parasitic coupling effects between superconductive microstrip transmission lines and conclusions have been drawn about the critical coupling levels of several typical microstrip geometries. Here, basic RSFQ structures are investigated experimentally, which contain a Josephson transmission line stage with large inductance and can either trap or pass SFQ pulses. These structures are incorporated in critical microstrip layouts, thus being subjected to parasitic coupling. The bias levels are monitored at which the structures start to pass the SFQ pulses with and without coupling influences. Thus, the conclusions of our previous theoretical investigations are verified experimentally.