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Browse Prior Art Database

Current Switch Speed-up

IP.com Disclosure Number: IPCOM000121801D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 1 page(s) / 34K

Publishing Venue

IBM

Related People

Buhler, OR: AUTHOR [+2]

Abstract

This article describes a means to reduce the turn-on time of a current switch.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 100% of the total text.

Current Switch Speed-up

      This article describes a means to reduce the turn-on time of a
current switch.

      A current switch circuit is shown in the figure. (Prior art
current switches do not have a speed-up capacitor Cb.)  When the
control voltage Ein changes from above a bias voltage level Vb to
below Vb, the transistor Q1 changes from a conducting state to a
nonconducting state while transistor Q2 changes from a nonconducting
state to a conducting state. As a reasonable approximation, current
Ic changes from Ie to zero while current Io changes from zero to Ie.
The value of Ie is determined by a current source.

      Capacitance Ce causes a significant delay in the abovedescribed
action.  When Ein falls below Vb, the transistor Q1 turns off quickly
but transistor Q2 cannot turn on until Ce is sufficiently discharged
through the current source.  Capacitance Ce is normally the sum of
transistor and distributed capacitances.

      Capacitor Cb provides an additional discharge path for
capacitance Ce.  As a result, the addition of the capacitor Cb
significantly increases the circuit's switching speed.

      Disclosed anonymously.