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Reduction of Cross-Over Current in Active Pull-Down ECL Output Stage Via a New Negative Feedback Control

IP.com Disclosure Number: IPCOM000120039D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 4 page(s) / 111K

Publishing Venue

IBM

Related People

Toh, KY: AUTHOR

Abstract

Disclosed is an enhancement to the active pull-down (APD) ECL circuit by incorporating a negative feedback path from the output node to the switching control node of the pull-down transistor to eliminate or to reduce substantially the cross-over current observed in the output stage of the APD ECL circuit implementation proposed in (1).

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

Reduction of Cross-Over Current in Active Pull-Down ECL Output Stage
Via a New Negative Feedback Control

      Disclosed is an enhancement to the active pull-down (APD)
ECL circuit by incorporating a negative feedback path from the output
node to the switching control node of the pull-down transistor to
eliminate or to reduce substantially the cross-over current observed
in the output stage of the APD ECL circuit implementation proposed in
(1).

      The APD ECL circuit implementation described in (1) (Fig. 1),
has no control of the output cross-over current, because the
pull-down switching control is in an opened loop.  Cross-over current
occurs when the output VOUT goes below the output low-level VOL,
which enables Q3 to turn on, resulting in a large cross-over current
flowing from Q3 to Q4 .  This cross-over current increases
substantially when the loading is reduced from the designed value.
Cross-over current is not desirable because it increases the AC-power
consumption and increases bus noises.

      The proposed enhancement is shown in Fig. 3.  This consists of
the APD ECL implementation (3) with the added feedback path between
the output node and the source of the base drive control to the pull-
down transistor Q4 .  As an illustration, the feedback path shown in
Fig. 3 consists of resistor RP and a PNP transistor QP between node A
and VT .  The feedback control is from the output node to the base of
the QP .  The operation and biasing control of the basic circuit
without the feedback path have been described in (2,3).  With the
negative feedback circuit added, when VOUT goes below the desired
VOL, QP turns on so that the source of the base drive at node A
is removed. This eliminates or reduces substantially the cross-over
current, even when the load capacitance is reduced significantly from
the designed value.  Fig. 4 shows the...