Circuits

The DC/DC-converter is the smallest digital circuit in RSFQ electronics. It is composed by a DC/SFQ converter, several number of JTL's and a SFQ/DC-converter.

The DC/SFQ-converter generates one SFQ pulse per raising ramp of the input current. So there is one toggle of the output state per period of the input signal. An amplifier is in use to amplify the output signal of the SFQ/DC-converter by 60 dB. That's why the oscilloscope detected a voltage signal nearly 150 mV while the signal strength of the SFQ/DC is 150 μV.

The input current has a higher amplitude. Now there are three SFQ pulses generated per raising ramp of the input current, thus the output state flips three times per period.

At one period of the input signal the output changed the state seven times. The amplitude on the picture appears smaller because of the different measuring range.

The DFF was the topic of the first workshop problem of the FLUXONICS Design workshop The DC/TFF/DC-circuit is composed of a DFF inside a DC/DC-converter. This electronics enabled a quantum-precise analysis of the embedded Flip-Flop.

The DC/TFF/DC circuit is composed of a Toggle Flip-Flop inside a DC/DC-converter. This electronics enabled a quantum-precise analysis of the embedded Flip-Flop.

The following pictures illustrate several oscilloscope screenshots of the experimental analysis. While channel 2 displays the input signal, channel 1 is showing the output signal of the circuit. Thereby 1 V input voltage corresponds with 1 mA input current.

An amplifier which enforced the signal by 60 dB was connected between the SFQ/DC-converter and the oscilloscope. This means that the 115 mV amplitude of the output signal corresponds with an output voltage of 115 μV produced by the RSFQ-circuit.

The function illustrate by this picture is similar to that one of the DC/DC-converter. The DC/SFQ-converter produces a SFQ-pulse per every raising ramp of the input current. Every pulse is transferred by the JTL to the Toggle Flip-Flop but only every other is leaving this cell towards the SFQ/DC-converter. Thus the input frequency of the SFQ/DC is the half of the output frequency of the DC/SFQ. The output voltage state of the SFQ/DC changes with every SFQ pulse which is reaching the cell. Therefore the output frequency of this circuit is a quarter of the input frequency as you can recognize.

The operation displayed in this photograph is simimlar to that one mentioned above. The input signal measured by channel 2 is the only difference. This time the input signal is provided by a DSP which is producing a voltage pulse sequence. Thus the circuit is driven by a signal with the same frequnecy but a higher slew rate. As you recognize this didn't effected the functionality of the RSFQ-electronics. Because from the point of view of the test circuit it is still a slow slew rate.

For a better understanding a section of this diagramm is shown below. In that graphic the generation of a SFQ pulse is marked by the vertical lines. For a better overview only a selection of such events is distinguished.