Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
1999-09-30
2002-04-23
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
C345S179000, C178S018010, C178S018030
Reexamination Certificate
active
06377248
ABSTRACT:
The invention concerns a stylus for use with a digitizing pad. Such pads can take the form of a transparent overlay atop the display of a portable computer.
BACKGROUND OF THE INVENTION
FIG. 1
is a highly simplified view of a digitizing pad
3
and its associated stylus
6
. There are four current-to-voltage amplifiers (labeled I-to-V), one at each corner. The stylus
6
, when activated, produces a signal
9
, as indicated in FIG.
2
. This signal induces currents I
1
-I
4
, which are detected by the I-to-V amplifiers.
The I-to-V amplifiers each produce a voltage indicative of the size its respective current. Processing circuitry, known in the art, receives the voltage signals, and computes the position of the stylus signal
6
, based on the voltage signals.
The currents I
1
-I
4
are induced because the stylus
6
acts as one plate of a capacitor. The digitizing pad (which bears a resistive surface of a material such as indium tin oxide) acts as the other plate. As
FIG. 3
indicates, when negative charge is applied to the tip
2
of the stylus
6
, a positive charge is induced on the surface of the pad
6
. Currents I
1
-I
4
supply this positive charge.
Conversely, as in
FIG. 4
, a positive charge on the tip
2
of the stylus
6
induces a negative charge on the pad. The currents I
1
-I
4
supply this negative charge.
The relative magnitudes of the currents depend on the position of the stylus. When the stylus is located as shown in
FIG. 5
, current I
1
is the largest, current I
4
is next largest, and currents I
2
and I
3
are nearly the same.
When the stylus is located as shown in
FIG. 6
, current I
4
is the largest, current I
1
is next, and so on. The differences in current magnitudes cause differences in the voltages produced by the I-to-V amplifiers of FIG.
2
.
Noise
The I-to-V amplifiers produce other, unwanted, signals, in addition to those generated by the stylus. For example, nearby cathode ray tubes, fluorescent lights, and electric motors induce charge on the digitizing pad. Also, “static electricity,” can be applied to the pad when touched by a user, especially when the ambient air is dry.
Because of the presence of the unwanted signals, which are called “noise,” it is desirable to use a stylus which generates a signal which is as large as possible, so that the stylus signal stands out from the noise signals. That is, the signal-to-noise ratio should be maximized.
If size and power consumption posed no limitations, then attaining a large signal-to-noise ratio would be no problem. However, the stylus is designed for portability. It must be small (about the size of a pencil) and it must operate on batteries. Operating on batteries, it must consume little power, in order to extend battery life.
Obtaining a high signal-to-noise ratio from such a stylus is not a trivial problem.
Objects of the Invention
An object of the invention is to provide an improved stylus for a digitizing pad.
A further object of the invention is to provide an improved stylus for a portable digitizing pad, which produces a large position signal.
REFERENCES:
patent: 3887767 (1975-06-01), Miller
patent: 4423286 (1983-12-01), Bergeron
patent: 5178010 (1993-01-01), Holzel
patent: 5528002 (1996-06-01), Katabami
patent: 5736980 (1998-04-01), Iguchi et al.
patent: 5945639 (1999-08-01), Patow et al.
patent: 5952999 (1999-09-01), Makinwa
patent: 5994651 (1999-11-01), Partow et al.
patent: 6081259 (2000-06-01), Teterwa
patent: 6140999 (2000-10-01), Yamada
patent: 6180894 (2001-01-01), Chao et al.
Partow Tony S.
Stanchak Carl M.
Hjerpe Richard
Nguyen Kimnhung
Townsend and Townsend / and Crew LLP
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