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ECL/DCS Circuits with Cross-Coupled Active-Pull-Down Emitter-Follower Stage

IP.com Disclosure Number: IPCOM000105259D
Original Publication Date: 1993-Jul-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 4 page(s) / 93K

Publishing Venue

IBM

Related People

Anderson, CJ: AUTHOR [+2]

Abstract

Disclosed is a cross-coupled active-pull-down scheme for ECL/DCS circuits which eliminates the extra biasing devices and power for the active-pull-down transistor and preserves the emitter-dotting capability.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

ECL/DCS Circuits with Cross-Coupled Active-Pull-Down Emitter-Follower Stage

      Disclosed is a cross-coupled active-pull-down scheme for
ECL/DCS circuits which eliminates the extra biasing devices and power
for the active-pull-down transistor and preserves the emitter-dotting
capability.

      Recently, various active-pull-down schemes have been pursued to
reduce the power consumption and improve the pull-down delay of the
emitter-follower stage in high-speed ECL/DCS circuits [*].  These
schemes, however, have the following drawbacks:  (1) for the
AC-coupled scheme (Fig. 1) special element (i.e., capacitor) is
needed [*], (2) additional devices are needed to implement the
biasing circuit for the active-pull-down transistor, (3) the power
consumption for the biasing circuit is wasted, and (4)
emitter-dotting is prohibited, thus limiting the application of these
schemes.

      This disclosure describes a DC cross-coupled active-pull-down
scheme for ECL and DCS circuits (Figs. 2(a) and 2(b), respectively).
The scheme utilizes a (DC) cross-coupled transistor pair  (Q sub D,L
and Q sub D,R) as the active-pull-down devices.  Resistors R sub D,L
and R sub D,R are used to set the steady-state biasing currents for
the emitter-follower stages.  As shown in the figure, when the input
is at 'High', the output node OUT is at 'Low' (-0.25V as shown) and Q
sub D,R is at cut-in condition (barely on with almost no current).

On the other hand, the 'OUT'bar node is at 'High' (0.25V) and thus
there is a steady-state current through Q sub D,L.  When the current
switch switches, the output node rises to 'High', and provides a very
strong base drive to turn Q sub D,R on heavily.  The resulting large
dynamic current from Q sub D,R not only pulls node 'OU...