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Ramp Driven Differential Sense Amplifier

IP.com Disclosure Number: IPCOM000050184D
Original Publication Date: 1982-Sep-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 36K

Publishing Venue

IBM

Related People

Wolf, PH: AUTHOR

Abstract

A sense amplifier employing Josephson junctions is proposed that is capable of detecting the presence of very small currents in the order of a few microamperes. The circuit comprises a sense junction and a dummy junction operated in a differential mode. The input current to be sensed as well as a ramp signal are applied to both junctions. The use of the latter signal prevents noise disturbances and causes the junctions to switch to the voltage state. Depending on whether an input current is present, either the sense or the dummy junction switches first.

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Ramp Driven Differential Sense Amplifier

A sense amplifier employing Josephson junctions is proposed that is capable of detecting the presence of very small currents in the order of a few microamperes. The circuit comprises a sense junction and a dummy junction operated in a differential mode. The input current to be sensed as well as a ramp signal are applied to both junctions. The use of the latter signal prevents noise disturbances and causes the junctions to switch to the voltage state.

Depending on whether an input current is present, either the sense or the dummy junction switches first.

The circuit of Fig. 1 consists of a sense junction J(s) and a dummy junction J(d), both of the same size. The input current is supplied to the junctions via a control line. The winding is of opposite sense at the dummy junction as compared to that at the sense junction. The maximum Josephson current of both junctions is, for instance, 100 MuA; they are biased at approximately 60 MuA, i.e., they cannot be switched by thermal noise signals. The ramp signal, triangular or trapezoidal, is applied to both junctions via a second control line which has the same winding sense at both junctions.

This signal is sufficiently large to switch the junctions. In the sense junction, the effects of the input current and of the ramp signal are added; in the dummy junction, the input signal substracts.

Therefore, if an input signal is present, the sense junction J(s) switches first, followed by the dummy junction J(d). With no input signal, both junctions would switch simultaneously, which is undesired. To avoid this, the dummy junction is biased so that, in the absence of an input signal, it always switches first. The same can be achieved by using a smaller dummy junction and eliminating the bias...