Browse Prior Art Database

Improved Complimentary Metal Oxide Semiconductor Off Chip Driver

IP.com Disclosure Number: IPCOM000114264D
Original Publication Date: 1994-Dec-01
Included in the Prior Art Database: 2005-Mar-28
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Gemar, JR: AUTHOR [+2]

Abstract

Described is a method of providing faster Complimentary Metal Oxide Semiconductor (CMOS) drivers without increasing the switching noise resulting from the drivers switching.

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

Improved Complimentary Metal Oxide Semiconductor Off Chip Driver

      Described is a method of providing faster Complimentary Metal
Oxide Semiconductor (CMOS) drivers without increasing the switching
noise resulting from the drivers switching.

      The rate at which drivers of a given impedance are turned on
limits the number of such drivers that may be switched at the same
time.  Ground (or Vdd) inductive bounce for this number of drivers
and a given package sets the limit.  The dv/dt of the gate voltage of
the output FET determines how fast the driver ramps up its current.
No current flows until the gate voltage is above the threshold of the
device, so the time spent charging the gate from zero volts to the
threshold is wasted.

      Note in the Figure that only the "pulldown" half of a CMOS
driver is shown.  A "pullup" circuit is implied, with similar
circuitry.

      To solve the problem of the wasted time, a diode is placed in
series with the FETs that turn off the output FET (QNOUT in the
Figure).  Signal Disable2 normally keeps QP1 conducting and the path
through QP1, R1, and QN1/QN2 provides a bias current for the diode
when QNOUT is "off".  The diode voltage approximates the threshold
voltage of QNOUT and keeps it close to turning on.  Alternatively, R1
could be connected directly to the anode of the diode - the purpose
of QP1/R1 is to keep a trickle current running through the diode to
keep it forward biased.  When input data goes low,...