Ym. Zhang et al., HIGH-T-C SUPERCONDUCTOR OVERSAMPLED DELTA-MODULATOR FOR ANALOG-TO-DIGITAL CONVERTERS, IEEE transactions on applied superconductivity, 7(2), 1997, pp. 2292-2295
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.