Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
2001-07-19
2003-09-16
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
Reexamination Certificate
active
06621487
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a circuit for generating touch detection signals and a locator device. More particularly, the invention relates to a locator device of such a type that a pair of electrodes in a grid pattern are scanned as a pair of capacitors whereby a touch detection signal having two peaks, one being greater and the other smaller than a specified reference level, is generated as a detection signal for the area around the touched electrode and its position is detected on the basis of this detection signal, characterized in that erroneous touch detection can be prevented by reducing or suppressing the variations in the offset of an electric current from the current outputting circuit which generates touch detection signals. The invention also relates to a circuit and a method for generating such touch detection signals.
The locator device is used as a substitute pointing device for the mouse, track ball and quick pointer on a computer system. It has a an electrostatic sensor portion comprising multiple X and Y electrodes arranged in a grid pattern and the position of a touched electrode is detected by sensing the difference in capacitance between adjacent electrodes in pair. For detecting the position of the touched electrode, X or Y electrodes are scanned, usually with a pair of adjacent electrodes taken as a set. The difference in capacitance between two capacitors formed by a pair of electrodes is detected as a difference in charge current by means of a charge current detector circuit and output as a touch detection signal.
If the X and Y electrodes in the electrostatic sensor portion are stripe electrodes thinner than the width of a finger which touches them, the capacitance of the touched electrode decreases because the electric lines of force between X or Y electrodes are interrupted by the finger. As a result, there occurs a change in the difference of capacitance between the touched electrode and the adjacent one which is either upstream or downstream of it. The difference in capacitance is positive and increases in the area upstream of the touched electrode. The difference then decreases and becomes zero in the touch position of the finger (its center portion) and thereafter increases taking a negative value. The difference then decreases to become zero again. This is the characteristic of the touch detection signal detected with the charge current detector circuit in the locator device. Briefly, the touch detection signal obtained by scanning X or Y electrode pairs with the charge current detector circuit varies in the scan direction such that two peaks occur with reference to a specified level, one being greater and the other smaller.
The touch detection signal generally described above is generated by a circuit of the type shown in
FIG. 2
which receives a charge current as obtained from each electrode.
FIG. 2
is a block diagram primarily for a charge current detector circuit
10
in a locator device which generates touch detection signals. Indicated by
11
is the electrostatic sensor portion (touching portion) of the charge current detector circuit;
12
is a multiplexer;
13
is a pulse drive circuit consisting of an X-side drive circuit and a Y-side drive circuit;
14
is a connection switching circuit;
15
is a differential current generator circuit;
16
a,
16
b
and
16
c
are switching circuits;
17
is an integrator circuit;
18
is a control circuit; and
19
is an offset cancelling circuit. The integrator circuit
17
consists of an integrating capacitor Cs and a parallel-connected switch circuit SW for resetting the electric charges that have built up in the capacitor Cs. In the case shown, connection switching circuit
14
, differential current generator circuit
15
and switching circuits
16
a,
16
b
and
16
c
make up the charge current detector circuit.
Switching circuits
16
a
and
16
b
are provided between multiplexer
12
and connection switching circuit
14
and as indicated by the one-long-and-one-short dashed line, switching circuits
16
a
and
16
b
and subsequent circuits including connection switching circuit
14
are assembled in an IC. Among these circuits, switching circuit
16
c
is provided between differential current generator circuit
15
and integrator circuit
17
.
Electrostatic sensor portion
11
is a flat member which has multiple stripe X electrodes spaced in the X direction and multiple stripe Y electrodes spaced in the Y direction; these two electrode groups are provided in a face-to-face relationship and superposed one on the other with a dielectric resin spacer interposed.
Two adjacent electrodes of either X or Y group are successively selected as a pair and driven by pulses supplied from pulse drive circuit
13
. The electrodes of the other group are supplied with a voltage of constant level. The two selected electrodes of either group correspond to two capacitors Ca and Cb (see
FIG. 2
) in relation to the electrodes of the other group. The difference between the capacitances of these two capacitors is output as a current value from differential current generator circuit
15
.
If the stripe electrodes of either X or Y group are driven by pulses from the pulse drive circuit
13
, a differential pulse of positive polarity (charging current pulse) is generated in response to the rise of the drive pulse and a differential pulse of negative polarity (discharging current pulse) is generated in response to the fall of the drive pulse. Connection switching circuit
14
is used to get these two kinds of differential pulse (charge current) to have the same polarity; to this end, the connection to the input terminal at the positive phase of differential current generator circuit
15
and the connection to the input terminal at the negative phase are interchanged immediately before the rise and fall of the drive pulse. As a result, connection switching circuit
14
adjusts these two kinds of current to have a single polarity (inverts the discharging current to have a positive polarity) and outputs them to differential current generator circuit
15
. The timing signal necessary for this switching operation is supplied as a timing signal T from controller
18
.
When two adjacent electrodes in the Y direction as selected by multiplexer
12
are supplied with a drive pulse P, said drive pulse P is applied at one end N of each of the capacitors Ca and Cb which form a common junction (suppose N is initially for X electrodes). The other ends Na and Nb of the selected capacitors Ca and Cb (Na and Nb are initially for Y electrodes) are supplied to the (+) and (−) phase inputs, respectively, of differential current generator circuit
15
via multiplexer
12
and connection switching circuit
14
. Differential current generator circuit
15
is composed of a Gm amplifier (transconductance amplifier) and provided at the (+) phase terminal (positive phase input terminal) and the (−) phase terminal (inverse phase input terminal) with the voltage signals (for charge current) that were generated at the other ends Na and Nb, respectively, of capacitors Ca and Cb. The circuit
15
outputs a differential current value representing the potential difference between the two input signals. For details of the technology about the charge current detector circuit, see U.S. Pat. No. 6,075,520 issued to the same assignee.
Offset cancelling circuit
19
is operated under the control of control circuit
18
. In the absence of any signal input to differential current generator circuit
15
before scanning of electrostatic sensor portion
11
starts, offset cancelling circuit
19
sets the output of differential current generator circuit
15
at a reference level and adjusts the resulting output current to the value “zero”. Since the output of differential current generator circuit
15
is set to the reference level as a result of this offset cancelling operation, touch detection signals which vary along the scan direction in such a way that two peaks occur with reference to a specified level, on
Iwasaki Mitsuharu
Nagai Takashi
Hjerpe Richard
Mattingly Stanger & Malur, P.C.
Nguyen Francis
Rohm & Co., Ltd.
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