Superconductor modulator with very high sampling rate for analog to digital converters

An analog-to-digital modulator comprising:

• a feedback loop filter having a characteristic pass band and inputs that accept an external input signal and a modulator feedback signal, and a filter output that provides a filter output signal;
• a superconducting comparator comprising an analog input, a clock input, a digital output, and a threshold current, and
• a superconducting digital-to-analog converter with digital inputs and an analog output, the digital-to-analog converter being constructed and arranged to convert single flux quantum pulses applied to the inputs into analog signals at the analog output;
• wherein the filter is constructed and arranged to subtract the feedback signal from the external input signal and to filter the subtracted signal such that the filter output signal is attenuated when the subtracted signal is outside the pass band;
• wherein when a clock signal is applied to the clock input, each comparator samples an analog signal applied to the analog input, and generates a single flux quantum pulse at the digital output if the input current generated by the analog signal applied to the analog input is greater than the threshold current;
• wherein the analog signals are time integrated functions of the single flux quantum pulses;
• wherein the feedback loop filter, digital-to-analog converter, and superconducting comparator arranged within a feedback loop such that the filter output signal from the feedback loop filter is communicated to the analog input of the superconducting comparator such that the comparator generates the single flux quantum pulses at the digital output, which are communicated to the digital inputs of the digital-to-analog converter and therein converted to the analog signals at the analog output, which is in turn communicated via the feedback loop to the modulator feedback signal input of the feedback loop filter, and
• wherein the filter output being galvanically isolated from the analog input of the comparator.

A method for converting an analog input to a digital output comprising:

• receiving the analog input signal and a modulator feedback signal at respective inputs of a feedback loop filter, the filter having a characteristic pass band and outputting at a filter output a filter output signal;
• subtracting the feedback signal from the analog input signal;
• filtering the subtracted signal such that the filter output signal is attenuated when the subtracted signal is outside the pass band;
• receiving the filter output signal at an input of a superconducting comparator, the comparator having an analog input, a clock input, a digital output, and a characteristic threshold current;
• sampling the analog signal applied to the analog input of the comparator when a clock signal is applied to the clock input;
• generating a single flux quantum pulse at the digital output of the comparator if the input current generated by the analog signal applied to the analog input is greater than the threshold current of the comparator;
• receiving the digital output signal at the input of a superconducting digital-to-analog converter, the digital-to-analog converter having a digital input and an analog output;
• converting single flux quantum pulses applied to the input of the digital-to-analog converter into analog signal at the analog output;
• communicating the analog signal of the digital-to-analog converter via a feedback loop to the modulator feedback signal input of the feedback loop filter;
• wherein the analog signal of the digital-to-analog converter are time integrated functions of the single flux quantum pulses, and wherein the camparator and the digital-to-analog converter comprise over-damped Josephson junctions.