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Push-Pull Output DTL Circuit

IP.com Disclosure Number: IPCOM000041573D
Original Publication Date: 1984-Feb-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Askin, HO: AUTHOR [+2]

Abstract

This circuit is able to drive high capacitive loads faster and with higher up-level DC tolerances than the standard DTL (diode-transistor logic) circuit while using low power supply voltage. Diodes D3 and D4 together with transistor T3 and resistors R3 and R4 form a conventional DTL logic circuit. The remaining parts provide an output circuit with active pull-up, thus increasing circuit speed under large capacitive loads. Transistor T2 acts as the active pull-up device. Transistor T1 together with diodes D1 and D2 and resistor R1 form an inverter to obtain the correct polarity signal for the base of T2. Resistor R2 performs as both the collector load resistor to T1 and as the base resistor to T2. Diode D5 acts as a level shifter for the inverted signal.

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Push-Pull Output DTL Circuit

This circuit is able to drive high capacitive loads faster and with higher up-level DC tolerances than the standard DTL (diode-transistor logic) circuit while using low power supply voltage. Diodes D3 and D4 together with transistor T3 and resistors R3 and R4 form a conventional DTL logic circuit. The remaining parts provide an output circuit with active pull-up, thus increasing circuit speed under large capacitive loads. Transistor T2 acts as the active pull-up device. Transistor T1 together with diodes D1 and D2 and resistor R1 form an inverter to obtain the correct polarity signal for the base of T2. Resistor R2 performs as both the collector load resistor to T1 and as the base resistor to T2. Diode D5 acts as a level shifter for the inverted signal. The resistor values depend on the power level and delay characteristic desired. In general, R1 and R3 set the base bias for T1 and T3, respectively, and should be the largest resistors in the circuit and be approximately equal in value. Resistor R4 determines the output characteristics above VCC- 0.6 V and the circuit power dissipation when the output is in the low state. It is usually smaller than R1 and R3. The value of resistor R2 is the parallel combination of R1 and R4. D5 (a HSBD (high barrier Schottky barrier diode)) is used both to reduce power and to improve the performance. The resistor R4 helps pull up the output node to the proper supply voltage level, thereby increasing th...