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Controlled Output Ramp Rate Off-Chip Driver, Quiet Off-Chip Driver (QOCD)

IP.com Disclosure Number: IPCOM000100773D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 3 page(s) / 72K

Publishing Venue

IBM

Related People

Ceccherelli, JC: AUTHOR [+2]

Abstract

This article describes an off-chip driver which has a controlled ramp rate to reduce dv/dt, thus reducing the delta associated with simultaneous switching of many off-chip drivers.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 56% of the total text.

Controlled Output Ramp Rate Off-Chip Driver, Quiet Off-Chip Driver (QOCD)

       This article describes an off-chip driver which has a
controlled ramp rate to reduce dv/dt, thus reducing the delta
associated with simultaneous switching of many off-chip drivers.

      The output of the off-chip driver (OCD) is controlled by a
feedback capacitor C1 with a constant current, connected to the gates
of the output transistors Q5 and Q6 via the pass gates, as shown in
Fig.  1.  The constant current pre-driver (CCP) regulates the current
through the capacitor C1.  Since i = C dv/dt and, in this circuit, i
and C are constant, dv/dt will be determined by the values of i and
C.  Transient current through Q5 and Q6 during switching is
eliminated by allowing only one transistor to be active at a time.
This is accomplished by the timing of the pass gates Q1 and Q2 and
the clamp gates Q3 and Q4.  For example, when switching from low to
high, prior to the transition the input to PD1 is high.  The output
of PD1 is low, as is the output of PD3.  The CCP output is high.
Q1 and Q4 are off, and Q2 and Q3 are on.  The input of PD1
switches low, and the output of PD1 switches high.  This turns on Q1
and turns off Q2.  At this point, the gate to Q6 is floating.  Two
gate delays later (PD2 and PD3), the output of PD3 switches high.
This turns Q4 on and Q3 off.  Q6 is turned off by Q4 pulling its
gate to ground.  The gate of Q5 remains high via the output of the
CCP and Q1 (on)...