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Multiple Output-tap Josephson Voltage Standard
Abstract
We have invented a Josephson voltage standard with multiple independent simultaneous voltage outputs. That invention provides two or more voltage references that are generated simultaneously from the instrument (perhaps from a single voltage standard circuit or multiple circuits). This concept circumvents the need of two or multiple systems for applications that require fixed or variable voltage ratios, or dual signals (such as square waves and sine waves of similar rms voltage). As just one example of applications, this invention allows the potential wide dissemination of a compact dual output 1 V & 100 mV Josephson voltage standard, with the ability to calibrate a secondary voltage standard at 10 V through the use of a 10:1 self-calibrated resistive voltage divider. It also can be implemented in ac power metrology for power meter calibrations that require two reference signals and impedance ratio measurements that require amplitude and phase programmability.
patent description
The invention is a method for producing multiple voltage outputs simultaneously with single or multiple Josephson voltage circuits implemented in a single cryogenic system. The output voltages can be of fixed ratio, independently programmable, or frequency/phase locked for ac, power, and impedance applications. This invention can be applied to any type of Josephson voltage standards (JVS); dc voltages or stepwise approximated waveforms generated by a programmable Josephson voltage standards (PJVS), arbitrary waveforms generated by the Josephson arbitrary waveform synthesizer (JAWS), or dual RF signals for communications. This invention allows the simultaneous generation of fixed or variable voltage ratios based on the design chosen and the bias scheme adopted to operate the Josephson circuit(s). This invention is not limited in principle to only two independent voltage outputs but can be generalized to any integer number of voltage outputs as required by application. The implementation encompasses either a single chip design with multipole voltage taps or the use of multiple independent circuits/devices located within a single cryogenic vessel (dewar or cryostat). In addition, the instrument must have the appropriate additional wiring to bring the multiple additional reference voltages from cryogenic temperature to room temperature or to the appropriate temperature for the application (perhaps RF signal sources at millikelvin temperature for superconducting quantum computing or digital computing). This invention simplifies by at least a factor of two the complexity of JVS system when a voltage ratio is needed. Application of this invention includes, among others: generation of simultaneous voltage references, ratio calibrations, resistive or inductive voltage divider calibrations, reference voltage with arbitrary phase an amplitude for electric power standard calibration, impedance ratio measurement and phase standard calibration. With a single circuit, the multiple voltage taps are sharing a common node. For applications requiring fully floating voltage outputs, this limitation can be eliminated with the use of independent circuits. Another limitation of this invention is that the cooling capacity of the cryocooler, required to reach cryogenic temperature must be capable of accommodating the slightly increased heat load produced by the additional wiring and potentially the heat load of the additional circuits.
Features
This invention avoids the need to duplicate JVS systems if more than one voltage output is required for an application, thus reducing the complexity and the costs. In some applications such a multiple output signal voltage standard can provide self-calibration capabilities by use of the simultaneous voltage outputs. This invention is key for the implementation of a new compact JVS. A simultaneous 1 V and 100 mV JVS system provides the voltage references needed for calibration of a 10:1 voltage divider, which thereby extends the quantum-referenced calibration range from 1 V to 10 V. The 1 V- 100 mV compact JVS is intended for wide dissemination of the revised SI volt (without the need of external calibration). With a more affordable price tag than the current 10 V PJVS standards and full automation (turn-key), such compact JVS will certainly become a successful commercial product.
With two independent waveforms with accurate and programmable amplitudes, harmonic content, and relative phase settings, a dual output JAWS becomes a key reference instrument for multiple metrology and industrial applications. Foreseeable commercial applications of a dual output JAWS are, among others, impedance ratio calibrations, phase standard calibrations, and electric power calibrations.