JPH0675687A - Information input device - Google Patents

Abstract

PURPOSE:To obtain a superior S/N ratio and shorten the time of signal processing by software, and to make a cable relatively long by using a rectangular wave as a carrier for pulses and also using a tuning filter for an amplification part. CONSTITUTION:An X-side carrier switch 13 and a Y-side carrier switch 14 are applied with pulses like A from an oscillator 15 and electrode lines of a tablet 11 are applied with a signal having a waveform like B sequentially by means of the electrode line switching signal of a tablet controller 24. The signal having the waveform like B becomes a detection signal which is close to a sine wave like C at the detection electrode of a stylus pen 18 after electrostatic capacity coupling by removing an external noise by the RC integration circuit of the tablet electrode lines and the capacity of the capacity coupling. When the stylus pen 18 is made to abut on the tablet 11, a signal amplified by an intermediate frequency filter 19 and an amplifier 20 has a waveform like D and then has a waveform corresponding to position information like E through the synchronous detection of a detector 21, and then an amplifier 22 performs differential amplification.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information input device, and more specifically, simplifies the internal circuit configuration of a signal detection pen, a cursor, etc. as a coordinate pointing means in an electrostatic coupling type information input device, and reduces cost. It is about.

[0002]

2. Description of the Related Art In an electrostatic coupling type information input device, a tablet having electrode wires arranged at a predetermined interval in the coordinate axis direction and an insulating material are contacted to a desired position on the tablet for coordinate input. A detection electrode is provided on the coordinate pointing means such as an input pen and a cursor for performing. A sequential scanning signal is applied to each electrode line of the tablet, and at this time, so-called impedance conversion in which a minute voltage induced in the detection electrode is sent out with high impedance by an active element in the coordinate indicating means by capacitive coupling, The signal is led to the apparatus main body by a cable, where the signal is amplified and digitally converted and supplied to a calculating means composed of a microcomputer, and this calculating means calculates the contact position of the coordinate indicating means at that time. As a calculation means, Japanese Patent Publication No. 53-19380 and Japanese Patent Laid-Open No. 60
No. 181816 is known.

As another method, as known from Japanese Utility Model Application Laid-Open No. 1-133358, which is the applicant of the present application, the minute signal is received with low impedance and current-voltage conversion is performed, and finally the calculating means is used. There is a method of calculating the contact position of the coordinate designating means.

[0004]

In the conventional information input device, the scanning signal applied to the electrode line of the tablet is induced in the detecting means in the coordinate pointing means by the capacitive coupling. The coupling impedance is several hundred KΩ or more depending on the distance (thickness of the insulating material) between each electrode wire of the tablet and the detection electrode. Therefore, two methods of detecting the scanning signal have been considered. The former is a method of detecting the induced minute voltage as a voltage, which is a method of providing an impedance conversion circuit for receiving with a high impedance and outputting with a low impedance in the coordinate pointing means. The latter method is a method of inputting an induced minute voltage by a current, which is a current-voltage conversion capable of extremely reducing the input impedance, and the induced signal can be transmitted to the device body by a cable.

A method using the impedance conversion circuit will be described with reference to FIG. Tablet electrode wire 1
The scanning signal applied to is capacitively coupled with the detection electrode 2 with an insulating material sandwiched (equivalently shown in FIG. 4), and at this time, the coupling impedance Z ₁ (3) becomes several ₁₀₀ KΩ or more. . Therefore, in order to efficiently input the induced pulse voltage, it is necessary to increase the impedance Z ₂ (4), but if it is too high, external noise may be picked up and the signal waveform may be blunted by the influence of stray capacitance. , Usually set to about 1 MΩ. In order to transmit the input signal to the apparatus main body by the cable 5, it is necessary to output with a low impedance in order to avoid the above influence. Therefore, in order to input voltage, the impedance conversion circuit 6 that inputs with high impedance and outputs with low impedance is required.

A method using current-voltage conversion will be described with reference to FIG. Operational amplifier (hereinafter referred to as OP amplifier) 8
The non-inverting terminal (+) is zero potential (ground), and the inverting terminal (-) and the detection electrode 7 are connected by a cable. OP
Since the point A of the amplifier 8 has an imaginary short-circuit with the point B, it has a zero potential, and the pulse current I induced in the detection electrode 7 is equivalent to being grounded via a cable.
In other words, the input impedance is 0Ω, ideally O
No current flows in the P amplifier 8 and it appears as a voltage V = -IR at the point C through the resistor R9. Thus, the input impedance can be made extremely low by the current-voltage conversion circuit.

However, in the former method of impedance conversion, an impedance conversion circuit is required inside the coordinate designating means, it is difficult to reduce the cost, and the cable also needs a power supply line for the impedance conversion circuit, so it can be made too thin. There was a problem that the operability was poor. Note that the above two methods are effective only for tablets having low resistance electrode lines, and a transparent tablet having a high resistance electrode line of ITO (tin-doped indium oxide) has a high effect when the pulse width of the pulse voltage is narrow. Since the resistance electrode line equivalently forms an RC integrating circuit, the pulse waveform is deformed due to its charging characteristic (RC time constant). Also, because of the high resistance, the attenuation rate of the pulse signal increased toward the end of the electrode wire of the tablet.

[0008]

Means for Solving the Problems The present invention has been made to solve the above conventional problems, and is a tablet in which a plurality of electrode lines in the X and Y axis directions are arranged, and each electrode of the tablet. Coordinate indicating means for detecting pulses applied to each electrode line and amplification for amplifying the signal detected by the coordinate indicating means by capacitively coupling to each electrode line of the tablet and a carrier switching circuit for sequentially applying pulses to the lines An information input device comprising a calculation unit and a calculation unit that calculates a contact position of the coordinate designating unit with a tablet from a signal amplified by the amplification unit, wherein a carrier wave of a pulse applied to each electrode wire of the tablet is used. It proposes an information input device using a rectangular wave and a tuning filter in the amplification part of the detected signal.

[0009]

In the present invention, a rectangular wave is used as the carrier wave of the pulse applied to the tablet, and a tuning filter by an intermediate frequency coil (IFT) is used in the amplification part of the detected signal. The coordinate indicating means is directly connected to the main body of the information input device by a cable without a built-in circuit.

[0010]

The present invention will be described with reference to the accompanying drawings. FIG. 1 shows an electrical block configuration. Here, reference numeral 10
Indicates a transmitting means, reference numeral 11 indicates a tablet as transmitting means, and reference numeral 12 indicates a receiving means. The transmission means 10 includes an X-side carrier switching device 13 and a Y-side carrier switching device 14.
And the electrode wires 16 and 17 of the tablet 11, respectively.
(Illustrated schematically) is connected, and a carrier wave from the oscillator 15 is applied. Under the control of the tablet control 24, the X, Y side carrier changeover switches 13, 14 sequentially apply the carrier waves from the oscillator 15 to the X, Y 16, 17 side electrode lines.

The signal receiving means 12 distributes the signal from the stylus pen 18 for signal detection to the pen switch circuit 23 and the filter 19. On the other hand, the detection signal applied to the filter 19 is the first amplifier 20, the detector 21,
The analog-digital converter (not shown) connected to the second amplifier 22 and included in the control circuit 25 is applied.

Next, the actual operation will be described. In the initial state, the X side carrier switching device 1 of the signal transmitting means 10
A pulse as shown in FIG. 2A is applied from the oscillator 15 to the 3, Y-side carrier switching device 14. Tablet control 2
The signal having the waveform as shown in FIG. 2B is sequentially applied to the electrode wire of the tablet 11 as the transmitting means by the electrode wire switching signal of No. 4. When the operator holds the stylus pen 18 in his / her hand and contacts the tablet 11, the waveform of the signal amplified by the filter 19 and the first amplifier 20 of the receiving means 12 becomes as shown in FIG. 2D, which is detected. By performing synchronous detection by the device 21, a waveform corresponding to the position information as shown in FIG. 2E is obtained and differentially amplified by the second amplifier 22 and converted into a digital signal by an analog-digital converter (not shown) included in the control circuit 25. After that, it is processed as position information by the control circuit 25 and output to a host computer (not shown).

Now, the process of the detected signal from the stylus pen 18 to the filter 19 and the first amplifier 20 will be described with reference to the equivalent circuit diagram of FIG. Tablet 1
The signal applied to the electrode line 1 of No. 1 has a waveform as shown in FIG. 2B. However, in the detection electrode 26 of the stylus pen after capacitive coupling, an RC integration circuit (not shown) in the tablet electrode line 1 and capacitive coupling If external noise is removed by the capacitance, the detection signal has a shape close to a sine wave as shown in FIG. 2C.

The sine wave containing the external noise is transmitted to the intermediate frequency coil 19 through the cable, and the latter has a larger winding ratio between the primary coil 27 and the secondary coil 28 of the intermediate frequency coil 19. Is set as
It becomes possible to boost the AC signal. Further, since the secondary coil 28 forms a parallel resonance circuit with the capacitor 29, it serves as a bandpass filter. From this, the sine wave and the external noise applied to the primary coil 27 of the intermediate frequency coil 19 are induced in the secondary coil 28 by the mutual induction action, but as described above, the secondary coil 28 boosts the voltage. However, since frequencies other than the sine wave are removed by the bandpass filter, only the sine wave of the primary coil 27 is selected by the secondary coil 28. Therefore, the first amplifier 20 amplifies a sine wave having a relatively good S / N ratio.

[0015]

Since the present invention has the above-described configuration, since the rectangular wave is used as the pulse carrier and the tuning filter is used in the amplifying unit, the rectangular wave is transformed into a sine wave by the tablet or capacitive coupling. However, since it is sufficient as a carrier wave for transmitting the position information and the position signal by the sine wave can be averaged by synchronous detection by the detection circuit, the S / N
The ratio is good and it has become possible to shorten the signal processing time by software. Further, since the tuned filter removes all but the sine wave having a constant period, it is not necessary to incorporate a circuit inside the stylus pen, and the cable can be made relatively long. It is also possible to detect the position information by setting the carrier frequency below the cut-off frequency and driving at 5V or higher due to the high-frequency elimination characteristics of the integrating circuit formed by the inter-electrode capacitance in the high impedance tablet. become.

[Brief description of drawings]

FIG. 1 Electrical block diagram

[Fig. 2] Signal waveform diagram

FIG. 3 is an equivalent circuit diagram of the present invention.

FIG. 4 Conventional equivalent circuit diagram

FIG. 5 Conventional equivalent circuit diagram

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 electrode wire 2 detection electrode 3 coupling impedance 4 impedance 5 cable 6 impedance conversion circuit 7 detection electrode 8 operational amplifier 9 resistance 10 transmission means 11 tablet 12 reception means 13 X side carrier switching unit 14 Y side carrier Switcher 15 Oscillator 16 X-side electrode wire 17 Y-side electrode wire 18 Stylus pen 19 Filter-20 First amplifier 21 Detector 22 Second amplifier 23 Pen switch circuit 24 Tablet control 25 Control circuit

Claims (1)

[Claims] 1. A tablet in which a plurality of electrode lines in the X and Y axis directions are arranged, a carrier switching circuit for sequentially applying a pulse to each electrode line of the tablet, and a capacitive coupling to each electrode line of the tablet. A coordinate indicating means for detecting a pulse applied to each electrode line, an amplifying section for amplifying a signal detected by the coordinate indicating means, and a contact of the coordinate indicating means with a tablet from the signal amplified by the amplifying section An information input device comprising a calculation unit for calculating a position, wherein a rectangular wave is used as a carrier wave of a pulse applied to each electrode wire of the tablet, and a tuning filter is used as an amplification unit of the detected signal. Information input device.