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Browse Prior Art Database

Tablet Digitizer Pen Burst Signal

IP.com Disclosure Number: IPCOM000115566D
Original Publication Date: 1995-May-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 79K

Publishing Venue

IBM

Related People

Beers, GE: AUTHOR [+3]

Abstract

Electostatic pen digitizer tablets are very prone to noise. Described is a method of synchronizing the transmission of a pen signal to a time periodic noise signal and then delaying the transmission of the pen signal from the LCD noise while bursting the pen signal data after the noise has settled out.

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

Tablet Digitizer Pen Burst Signal

      Electostatic pen digitizer tablets are very prone to noise.
Described is a method of synchronizing the transmission of a pen
signal to a time periodic noise signal and then delaying the
transmission of the pen signal from the LCD noise while bursting the
pen signal data after the noise has settled out.

      Tablet computers with digitizing screens using pen radiated
input are susceptible to noise coupling from the LCD driving signals,
power supply switching signals, backlight driver, and other system
digital noise sources.  The noise coupling mechanism is mostly
electrostatic and because of the large digitizing surface area much
noise is picked up and transferred to the low level input circuits of
the digitizer sensor amplifiers.  The pen signal being
electrostaticly coupled into the digitizer tablet also has to
overcome the large noise signal levels.  The pen x-y location signal
is starting out at a disadvantage because it is such a small level
signal when compared to the noise signal.

      This invention involves two parts.  The first is a method of
negating the noise signal induced from the Liquid Crystal Display
(LCD) device.  This is accomplished by waiting until the noise is
past in time and then sending out the pen signal.  In this way the
major effect of the LCD noise is eliminated.  The second part of the
invention deals with synchronizing the pen signal and the digitizer
in the quiet area between the LCD noise pulses.

      Fig. 1 shows the noise contribution to the digitizer sensor
signal.  It should be apparent that there is considerable noise
present.  In the actual test circuit the noise i...