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Constant Current TTL Circuit

IP.com Disclosure Number: IPCOM000086440D
Original Publication Date: 1976-Sep-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Chang, W: AUTHOR [+3]

Abstract

A Low-power transistor-transistor logic (TTL) circuit utilizing lateral PNP current sources, as base and collector load devices, affords a space saving over conventional TTL with resistor loads, and a speed improvement over integrated injection logic (IIL). Schottky diode D3 switches PNP TX4 load current from the collector of TX2 to the collector of TX1 when the circuit is switched from an on (output down) to an off state. PNP TX3 supplies current to the base and collector of TX1 through the Schottky barrier diode (SBD) D1 when any emitter of TX1 is pulled down. Otherwise, PNP TX3 supplies base and collector current to TX2 via SBDs D1 and D2. The PNPs, therefore, act as constant-current sources similar to IIL.

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Constant Current TTL Circuit

A Low-power transistor-transistor logic (TTL) circuit utilizing lateral PNP current sources, as base and collector load devices, affords a space saving over conventional TTL with resistor loads, and a speed improvement over integrated injection logic (IIL).

Schottky diode D3 switches PNP TX4 load current from the collector of TX2 to the collector of TX1 when the circuit is switched from an on (output down) to an off state. PNP TX3 supplies current to the base and collector of TX1 through the Schottky barrier diode (SBD) D1 when any emitter of TX1 is pulled down. Otherwise, PNP TX3 supplies base and collector current to TX2 via SBDs D1 and D2. The PNPs, therefore, act as constant-current sources similar to IIL.

The circuit can be operated with a reference of 0.6 volt and a current source supplying current to all PNP emitters, resulting in a circuit potential drop of -1.3 volts. The power delay product and layout area of the PNP TTL circuit provides an IIL/TTL compromise.

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