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Sub Nanosecond Generator with Continuously Variable Pulse Width Disclosure Number: IPCOM000073486D
Original Publication Date: 1970-Dec-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 2 page(s) / 39K

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Bono, RC: AUTHOR [+2]


The use of step recovery diodes allows this circuit to generate a sub-nanosecond pulse of variable duration.

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Sub Nanosecond Generator with Continuously Variable Pulse Width

The use of step recovery diodes allows this circuit to generate a sub- nanosecond pulse of variable duration.

In the quiescent state, T1 is off since its base and emitter are reverse biased. The diode D1 and the current source I1 maintain the collector of T1 at a potential approaching the collector base-avalanche voltage (BBV(CBO) with the emitter open circuited. Step recovery diode SRD2 and the resistor Ro return the transistor T1 to its quiescent state after avalanche. SRD2 is forward biased by the difference in potential Vdb-Vcc and Ro.

When the input generator triggers the base of T1 with a differentiated pulse (spike) of sufficient magnitude to overcome the reverse bias at the emitter, the transistor T1 switches to the avalanche mode. The collector pulls reverse current through SRD2 and Ro and the voltage at the collector drops. The emitter pulls current through R2, SRD1, C1 and Zo. Most of this current comes through the load impedance Zo and the Step Recovery Diode SRD1 so that an output pulse appears across Zo. The collector-to-emitter voltage quickly settles at the collector-to-emitter breakdown voltage BV(CBO) with the base open. In this mode, the transistor looks like a constant voltage source since BV(CBO) is very nearly constant over a wide range of avalanche currents. Diode D1 is now reverse biased, isolating the collector Vcc supply from the collector of T1. Diode SRD1 is conducting in the reverse direction. The length of time that SRD1 conducts in the reverse direction is proportional to the ratio of the forward and reverse currents through SRD1. The reverse current is governed by the avalanche collector voltage, the collector resistor Ro, the current source 11 and the load impedance Zo. For any given operating parameters, t...