5-Bit Quasi-Sinusoidal Voltage Waveform Synthesized Using Single-Flux-Quantum Pulse-Frequency Modulation

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.

I. Introduction

Josephson voltage standards have already been established for DC voltage, and are being extended to AC voltage [1] using programmable binary-weighted arrays [2] or pulse-driven arrays [3]. Digital-to-analog conversion using single-flux-quantum (SFQ) digital technologies is another candidate for AC voltage standards [4]–[8]. Because of its ultrafast digital signal processing [9], [10], an SFQ-based digital-to-analog converter (DAC) is expected to synthesize a sinusoidal voltage waveform beyond 1 MHz.