Browse Prior Art Database

Complimentary Mirrored Emitter Follower Driver

IP.com Disclosure Number: IPCOM000108881D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 1 page(s) / 48K

Publishing Venue

IBM

Related People

Banker, DC: AUTHOR [+4]

Abstract

A method of driving high capacitance loads in a controllable manner is disclosed. The use of complimentary emitter followers has been attempted in the past but generally suffers with nonsymmetry accompanied with difficulty in biasing and/or input drive, and unusual requirements of the PNP such as being fully isolated and having a high 'Ft'.

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Complimentary Mirrored Emitter Follower Driver

      A method of driving high capacitance loads in a controllable
manner is disclosed.  The use of complimentary emitter followers has
been attempted in the past but generally suffers with nonsymmetry
accompanied with difficulty in biasing and/or input drive, and
unusual requirements of the PNP such as being fully isolated and
having a high 'Ft'.

      In FIG. 1 a unique configuration of devices is depicted that
overcomes these difficulties.  Note that both PNP's have a collector
common with the substrate (GND).  A PNP appears in both the rising
and falling waveform and thus contributes greatly to the symmetry.
In analysis performed, the 'Ft' of the NPN was six times the 'Ft' of
the PNP.  The power was half that of an NPN- only technology while
the performance was two times that of the NPN emitter follower. The
output waveform (see FIG. 2) was a faithful reproduction of the input
waveform and did not present a loading problem to the circuit driving
this configuration.

      The DC currents through T1 and T2 can be offset from the
current through T3 and T4 by controlling the respective emitter sizes
(current mirroring).  It is a trivial exercise to adapt this
configuration for a second application, i.e., a Chip Output Driver.
Output transitions can be controlled by the application of
capacitance to the input of T1 and T2, or T3 and T4.

      Disclosed anonymously.