An SFQ digital to analog converter

We have developed and demonstrated a digital to analog converter DAC which uses an SFQ counter to precisely divide an input reference oscillator to produce a set of binary frequencies/voltages. The binary input gates the output SFQ pulses of the counter flip flops to a passive summing network, producing an analog output current. The DAC is asynchronous (no clock to reset latching circuits), low power, and requires only N equal matched resistors. We have built and tested a 4-bit Nb DAC with data clocking rates up to 1 GHz. Using the DAC we have generated arbitrary wave forms including ramps and sine waves. By measuring the harmonic content of sine wave outputs, we deduce values for the DAC linearity.