Unless otherwise stated, all
parameters here and below
are in PSCAN
units (suitable for numerical simulation).
Just like the T-flip-flop T1 has two stable states: "1" and "0" characterized respectively by the presence or absence of a magnetic flux quantum stored in the loop L6 - J1 - L7 - L4 - J9 - L10 - J5 - L9. Each pulse arriving at A switches the T1 state.
An input A arriving in state "0" also produces an output pulse at the output C. This happens every other odd-numbered input pulse after the last reset.
A pulse arriving at the input DR resets T1 to the state "0". In state "1" it also produces an output pulse at the output S.
In the state "0" a pulse from DR simply flips J11, in state "1" it flips J12 and J9 releasing the magnetic flux quantum and changing the state to "0".
In the state "0" a pulse from the input A flips J1, J4 and J2 switching T1 to the state "1", in the state "1" it flips J3, J5 and J7 changing the state back to "0".
Here is the complete SFQHDL script for T1.
View online the files necessary to simulate the circuit with PSCAN or download the whole compressed directory.
Switching of the JJ /CB1/J1 (red waveform in the upper set of waveforms) indicates the arrival of an SFQ pulse at the cell's input A. The red waveform on the lower graph corresponds to the input DR.
These waveforms were obtained with the following testbench:
The JTL elements are standard JTLs, the LOAD sub-circuits are the same standard JTLs with an inductance 1.25 and resistance 0.7 connected in series to the output. The values are in PSCAN units. The element CB is a kind of a merger with a load junction removed and the output terminal connected to the input A of T1. The schematics is given below.
The following table lists the static currents through terminals in this testing environment. The currents are in PSCAN units and the values are valid for all stable states of the circuit.
| Terminal Name | Current |
|---|---|
| sub-circuit T1 | |
| C, DR, S | < 0.20 |
| A | < 0.75 |
| sub-circuit CB | |
| A,B | < 0.05 |
| O | < 0.75 |
The terminals T1.A and CB.O are connected together. Because of the relatively high static current through them T1 will almost certainly require reoptimization if used without CB. The combination of T1 and CB used as a single circuit is likely to be more successful because of the relatively small values of static currents through its outside terminals. The combined circuit contains 12 Josephson junctions.
Another set of pictures explaining T1 operation with waveforms is available here.
This version was laid out for fabrication by Hypres, Inc.
Experimentally measured DC bias margins were approximately +/-30% both for single T1 cell and 4-bit register [1].
T1 was designed by Vassili Semenov. This page was prepared by Peter Litskevitch.
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