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Output Stage with Load Current Control

IP.com Disclosure Number: IPCOM000090761D
Original Publication Date: 1969-Jun-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Tertel, KG: AUTHOR

Abstract

Existing logic gates, such as the TTL type shown, consist of multiemitter input transistor T6, transistor T5 that provides phase-opposed signals, Existing logic gates, such as the TTL type shown, consist of multiemitter input transistor T6, transistor T5 that provides phase-opposed signals, adapter transistor T4 and transistors T1 and T2 of the actual output stage. Normally, T1 and T2 are alternatively conductive. To limit the output stage current in the transition periods during which T1 and T2 can be simultaneously conductive, orthodox circuits employ, for example, a limiting resistor of a typical value of 150 omega incorporated in the collector line.

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Output Stage with Load Current Control

Existing logic gates, such as the TTL type shown, consist of multiemitter input transistor T6, transistor T5 that provides phase-opposed signals, Existing logic gates, such as the TTL type shown, consist of multiemitter input transistor T6, transistor T5 that provides phase-opposed signals, adapter transistor T4 and transistors T1 and T2 of the actual output stage. Normally, T1 and T2 are alternatively conductive. To limit the output stage current in the transition periods during which T1 and T2 can be simultaneously conductive, orthodox circuits employ, for example, a limiting resistor of a typical value of 150 omega incorporated in the collector line. This current limiting resistor exerts a negative influence on the switching time of the stage when recharging, for example, capacitive load C applied to output terminals 5 and 6.

This output stage, has in comparison with the above limiting resistor, a very small resistor R4 of, for example, 30 omega connected between T1 and T2, parallel to which is arranged the control path of transistor T3. If the voltage drop over R4 exceeds the base-emitter threshold VBE of T3, the latter becomes conductive to control the base current of T1.

Recharging of C is effected by a constant load current 1 = VBE/R4. At an unchanged peak current, recharging proceeds more rapidly at a reduced rise time. In comparison with the normal TTL, this circuit also permits emitter dotting without speed loss. O...