International Business Machines Corporation

Transwitch Corporation

Phillip R Epley

Charles R Hoffman

Robert J Christopher

Joseph Curtis Diepenbrock

Barry L Stakely

Jon E Fox

Alexis Shishkoff

Donald J DaCosta

Jaideep Prakash

Ernesto Jaritz

Jerome P Dahl

An apparatus for correcting imperfectly equalized bipolar signals includes a delay line having a reset control, an AND gate, and a one-shot multivibrator. The apparatus is used in conjunction with an adaptive equalizer with the output of the adaptive equalizer being coupled to the input of the apparatus of the invention. More particularly, the output of the equalizer is coupled to the input and reset of the delay as well as to one input of the AND gate. The output of the delay line is coupled to the other input of the AND gate. The output of the AND gate is coupled to the input of the one-shot multivibrator and the output of the one-shot multivibrator is the corrected signal. The delay line is approximately equal to the pulse width of an erroneous pulse which is expected from over-equalization. When the delayed signal is compared to the original signal via the AND gate, narrow pulses are removed from the signal. The one-shot multivibrator is configured such that each pulse entering it from the output of the AND gate cause a pulse of a set length to be generated by the one-shot multivibrator. The output of the one-shot multivibrator therefore contains pulses of equal length. If a pulse from the equalizer is too narrow to be a valid bit, it causes the delay to reset.

Method and apparatus for correcting imperfectly equalized bipolar signals

A single-port network node transceiver that does not draw any substantial current from the network when it is powered-down, enabling it to meet the ISDN powered-down loading specification when built on a CMOS integrated circuit chip. The pull-up transistors of the transmitter output circuit each have means for shorting the well terminal to source terminal connection when the circuit is operating and opening the connection when the power to the transceiver is shut down. The opening of this connection prevents the well-substrate junction of the pull-up transistors from becoming forward biased and drawing current from the network when the power to the transceiver is off and there is voltage present on the network. The transceiver also includes a plurality of ESD overvoltage protection diodes in series between the power supply rail and each input/output terminal. Since multiple diodes are connected in series and their voltage drops are added together, the diodes also do not draw current from the network when the transceiver is powered down.

Single-port network node transceiver with powered-down protection

A high-speed data transport system for use in computers, switches, microprocessors or the like includes a low impedance differential bus and a plurality of transceivers connected to the bus. Each of the transceivers is provided with a driver circuit which places data onto the bus and a receiver for accepting data from the bus. The driver includes a pseudo-differential current driving circuit arrangement which sinks current from only one side of the bus while the other side of the differential bus is undisturbed. The receiver includes a differential comparator biased to a preferred output voltage level.

High speed bus transceiver with fault tolerant design for hot pluggable

A sensing apparatus for detecting impedance changes in a variable impedance matrix keyboard. A microcomputer is utilized to control the basic key intersection scanning and for accurately calibrating and adjusting the sensing threshold of the sense amplifier prior to testing each key intersection so that the effects of stray impedance and varying voltage levels may be compensated for. The micro computer supplies sense amplifier sensitivity threshold selection address codes to set the sensing level for the amplifier. Trial drive pulses are applied to a reference capacitor and are gated to the sense amplifier while the sensing level thereof is varied until no output is obtained. This effectively adjusts the sensing circuits for variable voltage power fluctuations occurring over a short time and compensates for variable capacitive effects not associated with actual key switch movements. The micro computer also has a memory containing known stray capacitance values associated with a given keyboard design and these values are also used to compensate by modifying the sensing threshold above or below the calibrated sensing level achieved. Thisis done after driving and measuring the capacitance response until a zero output is obtained so that the sensing level may be individually set for each given key in the matrix at that precise level which can provide the highest non-saturating sensitivity level for the amount of stray capacitance known to be associated with the key and for the existing power and capacitance conditions as originally determined by checking the reference capacitor.

Program controlled capacitive keyboard variable threshold sensing system

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Raleigh, NC, United States of America

Phillip R Epley