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Bidirectional Pulser Circuit

IP.com Disclosure Number: IPCOM000046008D
Original Publication Date: 1983-May-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Buhler, OR: AUTHOR [+2]

Abstract

The circuit shown in Fig. 1 generates an output pulse for each transition, positive or negative, of an input signal. The width of the pulses is precisely controlled by the use of current sources to charge and discharge capacitor C and by the use of the VBE drops (baseto-- emitter voltages) on transistors Q1, Q2 and Q3 to provide a reference voltage switching point.

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Bidirectional Pulser Circuit

The circuit shown in Fig. 1 generates an output pulse for each transition, positive or negative, of an input signal. The width of the pulses is precisely controlled by the use of current sources to charge and discharge capacitor C and by the use of the VBE drops (baseto-- emitter voltages) on transistors Q1, Q2 and Q3 to provide a reference voltage switching point.

In operation, switch 10 is closed (conducting) when the input signal is down. Since current source 12 is twice the size of current source 14, a current equal to I is being pulled from capacitor C. The steady-state condition for voltage across capacitor C will be the point where transistor Q2 turns on, i.e., a voltage equal to -VBE. As shown in the waveforms of Fig. 2, the input signal is down, the output signal is down because Q2 is conducting and the voltage on the capacitor is - VBE.

When the positive-going transition of the input signal occurs, switch 10 opens. Capacitor C is now being charged up with a positive current I and its voltage is rising. As soon as the voltage on capacitor C rises above -VBE, transistor Q2 turns off. All of the transistors Q1, Q2 and Q3 are now off so the output signal rises to +VCC. When the voltage on capacitor C reaches +VBE, transistors Q1 and Q3 turn on, and the output voltage drops. The steady-state condition, when the input signal is high, is a voltage of +VBE across capacitor C, transistors Q1 and Q3 are on, and the output voltage is l...