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Josephson Device Oscillator Circuit

IP.com Disclosure Number: IPCOM000082192D
Original Publication Date: 1974-Oct-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 4 page(s) / 85K

Publishing Venue

IBM

Related People

Terlep, KD: AUTHOR

Abstract

Figs. 1 and 2 show a Josephson device oscillator circuit and timing diagram utilizing coupled, bistable superconducting loops. Each loop can have current, Iin, flowing in the right branch or left branch depending upon, respectively, whether the device within the left branch or right branch had been previously switched to it's resistive state. A third device, JR, is shown in each loop for oscillator reset as described below. Loop currents are defined and device control currents are shown adjacent to the devices. Fig. 3 shows the I gate vs. I control characteristic assumed for all devices except JR. Points that should be noted are: 1. The devices will switch for I gate of magnitude Io and I control in the same direction and of magnitude Io/2. Each device has a fan-in of two. 2.

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Josephson Device Oscillator Circuit

Figs. 1 and 2 show a Josephson device oscillator circuit and timing diagram utilizing coupled, bistable superconducting loops. Each loop can have current, Iin, flowing in the right branch or left branch depending upon, respectively, whether the device within the left branch or right branch had been previously switched to it's resistive state. A third device, JR, is shown in each loop for oscillator reset as described below. Loop currents are defined and device control currents are shown adjacent to the devices. Fig. 3 shows the I gate vs. I control characteristic assumed for all devices except JR. Points that should be noted are:
1. The devices will switch for I gate of magnitude Io and

I control in the same direction and of magnitude Io/2.

Each device has a fan-in of two.
2. Devices will not switch for I control of magnitude Io or

less if in the opposite direction to the gate-current.
3. The example in Fig. 1 shows three interacting loops A, B,

and C with branch currents of loop A controlling the

devices in loop B and, thus, it's branch currents. The

branch currents of loop B, in turn, control devices in loop

C as shown, and finally, branch currents of loop C control

the devices of loop A. This "feedback" of control permits

controlled oscillation of currents in each loop branch

between magnitudes of Imin and Io-Imin. For further

discussion of circuit operation, assume that Imin is

approximately zero and ignore it.
4. Each loop in Fig. 1 has the controls applied in the

opposite-direction for the device in the left-hand branch.
5. All loops have the control currents applied in the same

direction for devices in the right-hand branches.
6. As compared to loops B and C, loop A has its devices

controlled by correspondingly reversed branch currents.

At time, To, control current Is is applied as shown in Fig. 2 with no effect, until sometime subsequent to T1 when each device in the right hand branch switches, transferring current Io to the left-hand branch of each loop. Each of the devices in the left-hand branches has opposite direction control, Is, ensuring that they do not switch. At time T1, Iin=Io is applied as shown.

At time T2, Is is removed permitting control to be taken by the interacting loop currents. The first device to switch is the one in the left-hand branch of loop A which now has > or = Io/2 control current from I2C. With this switching, current transfer is initiated and when I1A reaches Io/2, it causes switching of the device it controls in loop B again rerouting current, etc. Examination of Fig. 2 shows vertical arrows at the time base of each branch current. An arrow pointing awa...