HIGH-T-C SUPERCONDUCTOR OVERSAMPLED DELTA-MODULATOR FOR ANALOG-TO-DIGITAL CONVERTERS

Based on a single-level YBCO thin film topology and seven bicrystal gr ain-boundary junctions, a high temperature superconductor delta modula tor for analog-to-digital converters has been designed, fabricated, an d tested. A single bit quantizer based on a quantum flux parametron (Q FP) comparator is used for the modulator. A large superconducting indu ctor is used both for the signal input and for the feedback. A small r esistor is chosen for connecting the comparator to the read-out sectio n. The oversampling provides large input signal bandwidth with high dy namic range. Circuit simulations prove the concept elf the design. The effective LSB and MSB of the modulator are discussed in terms of inpu t inductance, junction critical current, and QFP noise current. The de nsity of latched output pulses is proportional to the change of input amplitude. Au wires were employed to make crossover of bias lines. Alt hough this modulator did not function as expected for low-speed measur ements, it shows the proper latching behavior of the output section at 4.2K and 35K.