Look-back analog to digital converter

Abstract

In an analog-to-digital converter implemented in logic operating on the multiple lobes of a threshold curve, such as Josephson SQUIDs, two sampling registers are provided with sufficient offset to guarantee stability at sampling in one or the other regardless of other factors. Knowledge of bit value of the next lower bit order position permits determination of which sampling is valid. Encoder logic selects the valid sampling register retroactively. Each sampling register bit order position has two sampling SQUIDs and latching self-gated ANDs. Bias values are provided at higher orders to increment the phase offset so as to ensure low-to-high order readout. The lowest two bit orders may be implemented in simplified logic, effectively giving two bit order positions for logic and SQUIDs equal to that of one higher order bit position.