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Physics Procedia

4-bit Bipolar Triangle Voltage Waveform Generator Using Single-Flux-Quantum Circuit

Tomoki Watanabe, Yoshitaka Takahashi, Hiroshi Shimada, Masaaki Maezawa, Yoshinao Mizugaki

Published Jan 1, 2015• 8 citations
Publisher

Abstract

SFQ digital-to-analog converters (DACs) are one of the candidates for AC voltage standards. We have proposed SFQ-DACs based on frequency modulation (FM). Bipolar output is required for applications of AC voltage standards, while our previous SFQ-DACs generated only positive voltages. In this paper, we present our design of a 4-bit bipolar triangle voltage waveform generator comprising an SFQ-DAC. The waveform generator has two output ports. Synthesized half-period waveforms are alternately generated in one of the output ports. The bipolar output is realized by observing the differential voltage between the ports. We confirmed a 72-μVPP bipolar triangle voltage waveform at the frequency of 35.7 Hz.

DOI
10.1016/j.phpro.2015.05.120

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IEICE Electronics Express•May 15, 2022•1 citation
SFQ digital-to-analog converters (DACs) are one of the candidates for AC voltage standards. We have proposed SFQ-DACs based on frequency modulation (FM). Bipolar output is required for applications of AC voltage standards, while our previous SFQ-DACs generated only positive voltages. In this paper, we present our design of a 4-bit bipolar triangle voltage waveform generator comprising an SFQ-DAC. The waveform generator has two output ports. Synthesized half-period waveforms are alternately generated in one of the output ports. The bipolar output is realized by observing the differential voltage between the ports. We confirmed a 72-μVPP bipolar triangle voltage waveform at the frequency of 35.7 Hz.
We present a single-flux-quantum (SFQ)-based digital-to-analog converter (DAC) generating bipolar output voltages, in which the key component is a polarity-switchable double-flux-quantum amplifier (PS-DFQA). The DAC comprised a dc/SFQ converter, an 8-bit variable pulse-number multiplier (PNM), and a ±8-fold PS-DFQA integrated on a single chip. SFQ pulse-frequency modulation was employed to realize variable output voltage amplitude, for which the multiplication factor of the variable-PNM was controlled by a commercial data generator situated at room temperature. The variable-PNM realized 8-bit resolution with a multiplication factor between 0 and 255. Bias currents fed to the ±8-fold PS-DFQA were polarity switched in synchronization with the digital code for the variable-PNM. The whole circuits including I/O elements were designed using SFQ cell libraries, and fabricated using a niobium integration process. Sinusoidal bipolar voltage waveform of 0.38 mVpp was demonstrated using a reference signal source of 43.94 MHz.
Precise voltage generation is a unique feature of superconducting single-flux-quantum (SFQ) circuits, and hence, several SFQ-based digital-to-analog converters (DACs) have been designed for metrological applications. In this letter, we propose a dual double-flux-quantum amplifier (dual-DFQA) that extends DAC output voltage from unipolar to bipolar. An SFQ-based DAC comprising a 4-bit variable pulse number multiplier and a ±20-fold dual-DFQA is fabricated using a niobium integration technology. A 1-kHz, ±0.29-mV sinusoidal voltage waveform is successfully synthesized.
Single-flux-quantum (SFQ) circuits can generate highly accurate average voltage. We have developed SFQ digital-to-analog converters (DACs) for application of new ac voltage standards. In this paper, we present a bipolar voltage amplifier (BVA) based on a double flux quantum amplifier (DFQA) for generation of intrinsic bipolar voltage in an SFQ-DAC. The BVA realizes the identical multiplication factors for the positive and negative output, whereas the conventional DFQA has different multiplication factors in the bipolar output. The BVA can be used for the output stage of the SFQ- DAC. We have designed a 19-fold BVA and confirmed that the 19-fold BVA operated for input frequency of up to 31.2 GHz in positive voltage output and 33.6 GHz in negative voltage output.
Synthesis of sinusoidal voltage waveform is a unique application in single-flux-quantum (SFQ) digital electronics. In this paper, the authors present a waveform synthesizer based on SFQ pulse-frequency modulation. It comprises a variable SFQ pulse-number-multiplier (PNM) and a code generator (CG) integrated on the same chip. The output voltage is determined by the multiplication factor in the variable-PNM, which is controlled by the code from the CG instead of room-temperature electronics. The variable-PNM realizes 5-bit resolution with the multiplication factors between 33 and 64. The CG generates the 5-bit codes for 16-step quasi-sinusoidal waveform. The whole circuits including I/O elements are designed using an SFQ digital cell library, and fabricated using a niobium integration process. The modulation of the multiplication factor for the 16-step quasi-sinusoidal waveform is confirmed by counting SFQ pulses in the low-speed testing, whereas the voltage waveform of 11 μV peak-to-valley is demonstrated using a high-speed SFQ input of 156.25 MHz.
Digital to analog converters based on the Josephson effect are promising for voltage standards, because they produce voltage steps with ultimate precision and stability. In this paper, we describe a project to develop a Josephson D/A converter designed for synthesizing a sinusoidal waveform with metrological accuracy. The D/A converter is based on RSFQ (Rapid Single Flux Quantum) logic circuits, and consists of a frequency multiplier (FM), a pulse distributor (PD), and a number of voltage multipliers (VMs). Each VM circuit, corresponding to the n-th bit digital code, multiplies the number of SFQ pulses by a factor of 2/sup n/. By gating the input SFQ pulses from the FM to the VMs using the PD circuits, a programmable output voltage is obtained. Possible sources of uncertainties in the measurement of the rms value of the synthesized sine wave are discussed.
We designed and operated a 4-bit single-flux-quantum pulse-frequency modulator for bipolar D/A conversion. It was based on our previously-proposed “sum of selected bit sequence” configuration. Two functions, a synchronization scheme with a reference signal source and a complement number system for realization of bipolar output voltage, were implemented. A test circuit excluding the output analog stage (dual double-flux-quantum amplifier) was fabricated using a 10 kA/cm2 Nb/AlOx/Nb integration process. The synchronization function was evaluated in terms of the average voltages, which agreed well with the expected values. The bipolar D/A conversion was successfully emulated by using the positive and negative output signals. The maximum over-biased input voltage was determined to be 230 µV, of which the corresponding SFQ repetition frequency was 111 GHz.