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DTTL Push-Pull Driver

IP.com Disclosure Number: IPCOM000042474D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Boudon, G: AUTHOR [+2]

Abstract

The push-pull driver shown in Fig. 1, which operates under a low supply voltage, is compatible with conventional gates in TTL, DTTL, or DTL logic. It allows the delay of a DTTL gate to be reduced when the load capacity of the gate is high. When one of the inputs IN1 or IN2 is at a low level (Z 0.2 V) transistors T1 and T2 are OFF, which makes transistors T3 and T6 conductive. The low level at the output (OUT) is insured by means of transistor T6, since the conduction of transistor T3 prevents any current from flowing into T5. When the inputs IN1 and IN2 are at an up level, transistors T1 and T2 are ON, which makes T3 and T6 OFF. The level at OUT increases up to voltage Vc minus the base-to-emitter voltage VBE of transistor T5.

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DTTL Push-Pull Driver

The push-pull driver shown in Fig. 1, which operates under a low supply voltage, is compatible with conventional gates in TTL, DTTL, or DTL logic. It allows the delay of a DTTL gate to be reduced when the load capacity of the gate is high. When one of the inputs IN1 or IN2 is at a low level (Z 0.2 V) transistors T1 and T2 are OFF, which makes transistors T3 and T6 conductive. The low level at the output (OUT) is insured by means of transistor T6, since the conduction of transistor T3 prevents any current from flowing into T5. When the inputs IN1 and IN2 are at an up level, transistors T1 and T2 are ON, which makes T3 and T6 OFF. The level at OUT increases up to voltage Vc minus the base-to-emitter voltage VBE of transistor T5. To speed up the rising transition of the output voltage, diode-connected transistor T4 is forward biased when the output voltage is low and backward biased when the output voltage is high. The diffusion capacity (CB) of the collector-base junction of T4 is proportional to the current in this junction. This capacity is high and couples the collector of T3 to the base of T5 when the output voltage increases. In the transient period, the voltage at the base of T5 is higher than supply voltage VC, which causes an excess of the emitter current in transistor T5. Thus, the output capacity is loaded more rapidly. Transistors T1 and T2 have separate collectors in order to speed up the falling output transition. Fig. 2 shows the...