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Complementary Schottky Current Switch

IP.com Disclosure Number: IPCOM000052519D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 77K

Publishing Venue

IBM

Related People

Blumberg, RJ: AUTHOR [+3]

Abstract

The disclosed type of logic circuit offers increased circuit speed by using Schottky diodes in a complementary current switch application. The speed improvement is realized mainly by the smaller voltage level excursions of the current switch. In addition, lateral PNP transistors are used to replace load resistors in conventional current switch circuits of this type.

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Complementary Schottky Current Switch

The disclosed type of logic circuit offers increased circuit speed by using Schottky diodes in a complementary current switch application. The speed improvement is realized mainly by the smaller voltage level excursions of the current switch. In addition, lateral PNP transistors are used to replace load resistors in conventional current switch circuits of this type.

Fig. 1 shows the basic circuit configuration and the corresponding logic level scheme. T1 and T2, together with current source I NPN, form a conventional current switch. A and VR represent the signal and reference inputs, respectively; the outputs are phi and phi. Diodes D1-D4 are low barrier Schottky diodes (SBDs) with a forward voltage (VF) of about 250 mv at 0.25 mA. Transistors T3 and T4 are standard lateral PNPs, while T1 and T2 are standard NPNs. Current source I NPN sets the down or logical "0" level. Current source I PNP sets the up or logical "1" level. For proper circuit operation, I NPN should be >/- 2 I PNP. When input A is at a down level, current flows from T4 to T2, and from T3 through D3 and D2. When input A is at an up level, current flows from T3 to T1, and from T4 through D4 and D1 to T1.

Fig. 2 shows, on the right, the basic logic circuit of Fig. 1 which has been further simplified to allow for self-biasing of the PNP circuit section. This complementary circuit is designed to operate with I NPN = 2 I PNP. Adjusting I NPN externally will automat...