Agilent Technologies, Inc.

Hewlett-packard Company

Brian Cardanha

M Jason Welch

Kent R Townley

Dan Stotz

A multi-function output driver that may be used with at least two types of busses includes a multiplexer that shifts calibration bits to the pull-down transistors. This shifting changes which transistors of the transistor array are turned on when the pull-down drive transistors are driving. By changing which transistors are turned on, the impedance of the driver is changed. This shifting is used with a disable function on the pull-up drive-transistors to allow the driver to be used as an end-of-line termination, an open-drain driver, or as a source-terminated driver.

Integrated circuit with multi-function controlled impedance output drivers

The inventive mechanism provides a hysteresis margin to a comparator. The inventive mechanism generates two different voltage values, one high level and one low level, which forms the noise margin. The mechanism will select the proper level based on the output of the comparator. The comparator will then use the selected reference voltage, having either a slightly higher or lower level than a nominal reference value, as the reference voltage in its operations. The difference between each level and the nominal level is the added hysteresis noise margin. The inventive mechanism uses the higher voltage level when the output of the comparator is below the nominal reference voltage, and uses the lower voltage level when the output of the comparator is above the nominal reference voltage. Thus, a noise spike in the input signal would have to be larger than the margin provided by the mechanism, before causing the comparator to react to the noise in the signal. Since the mechanism is separate from the comparator, different comparators do not have be designed and tested. The mechanism can be disabled by a shorting some of the nodes of the mechanism together during the metal layer step of the device fabrication.

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Sunnyvale, CA, United States of America

Brian Cardanha