Automated Measurements of Low-Signal RSFQ Digital Circuits

| An integrated multipurpose setup for the automated testing of superconductor devices and circuits has been designed, implemented, and installed in the RSFQ Laboratory of the State University of New York at Stony Brook. The ex-tendible and modular design of the setup allows a wide variety of low-frequency superconductor experiments to be carried out including those that require immediate interaction between the setup and the researcher. The recent rapid progress in the eld of superconduc-tor electronics, particularly of Rapid Single Flux Quantum (RSFQ) logic and memory devices 1], has required adequate testing equipment that would exibly accommodate the needs of both analog and digital superconductor circuit designers. The following major features of an automated supercon-ductor testing setup (ASTS) are required in a typical research environment: a) robustness, b) easy conngurability of both the hardware and the software, c) modularity, d) reasonable data acquisition speed, and e) reasonable price. Minor but desirable features include a) simultaneous regulated dc power supply of several circuits, b) extraction of the resistance matrix and the resistive tree of a superconductor chip, c) measurements of dc I-V (current vs voltage) and-V (magnetic ux vs voltage) dependencies, d) immediate power spectrum analysis of signals, e) generation of digital test patterns and analysis of the digital response, f) calculation of one-and multi-dimensional parameter windows of the correct operation of devices, g) thermal removal of uxoids from superconductor chips, h) chip temperature control, i) long-term accumulation of acquired data, and j) adequate noise ltering, without excessive bandwidth reduction. The nature of the emerging superconductor electronics imposes certain additional requirements on a high-quality ASTS. First, the diierence between logical \0" and \1" in Niobium-based RSFQ circuits is between 150V and 2mV and is not likely to exceed tens of millivolts in the future. Thus, the RMS noise in digital output channels must be at most half this value, preferably less than 10V. The situation is more critical for analog measurements when even the noise of 0.5V may not be satisfactory. The internal clock frequency of superconductor circuits ranges from 1GHz to 700GHz. Semiconductor devices are not capable of picking up data at such a rate, but it is highly desirable that the acquisition bandwidth of an ASTS be as high as possible (100kHz and more). An important consideration is the number of I/O channels. Current SUNY standard speciies 40 contact pads per chip, and this number will be increased in …