JPH0637468Y2 - Information input device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an information input device, and more specifically, to an internal device such as a signal detection pen, a cursor or the like as a coordinate pointing means in an electrostatic coupling type information input device. The present invention relates to simplification of a circuit configuration and cost reduction.

[Prior Art] In an electrostatic coupling type information input device, a tablet having electrode lines arranged at predetermined intervals in the coordinate axis direction and a coordinate input by abutting at a desired position on the tablet via an insulating material. Input pen to perform
A detection electrode is provided. Then, a scanning signal is sequentially applied to the electrode lines of the tablet, and at this time, a minute voltage induced in the detection electrode by capacitive coupling is received by the active element in the coordinate pointing means with high impedance,
So-called impedance conversion for sending with low impedance is conducted, guided to the cable device main body, where the signal is amplified, digitally converted and supplied to the calculating means composed of a microcomputer, and this calculating means is brought into contact with the coordinate indicating means at that time. The position is calculated. As a calculation method, Japanese Patent Publication No. 53-193
No. 80, JP-A-60-181816 and the like are known.

[Problems to be Solved by the Invention] In the conventional information input device, the scanning signal applied to the electrode line of the tablet is induced in the detection means in the coordinate pointing means by capacitive coupling. Depending on the distance between the electrode wire of the tablet and the detection electrode (thickness of the insulating material), the coupling impedance becomes several hundreds KΩ or more, so that the voltage is detected in the coordinate designating means with high impedance and output with low impedance. There is a disadvantage that a circuit is required and it becomes difficult to reduce the price. Further, the cable also needs a power supply line for an impedance conversion circuit, which causes a problem that the operability is poor because it cannot be made too thin.

Here, a conventional signal detection method will be described with reference to FIG. The scanning signal applied to the electrode line of the tablet sandwiches the insulating material, and capacitively couples between the electrode line of the tablet and the detection electrode. At this time, the coupling impedance Z ₁ is several hundred KΩ.
That is all. Therefore, in order to efficiently input the induced pulse voltage, it is necessary to increase the input impedance Z ₂ , but if it is too high, external noise may be picked up and the signal waveform may be blunted by the effect of stray capacitance. It is set to about 1 MΩ. In order to transmit the input signal to the main body of the device with a cable, it is necessary to output with a low impedance in order to avoid the above influence. Therefore, in order to input voltage, it is necessary to provide an impedance conversion circuit that inputs with high impedance and outputs with low impedance.

[Means for Solving the Problems] The present invention has been made to solve the above conventional problems, and includes a tablet in which a plurality of electrode lines are arranged in the coordinate axis direction, and an electrode line of the tablet. A control unit for applying a scanning signal to the device, coordinate pointing means for capacitively coupling the scanning signal applied to the electrode line of the tablet for signal detection, and an amplification section for amplifying the signal detected by the coordinate pointing means. And an arithmetic unit for calculating the contact position of the coordinate designating unit with the tablet from the signal amplified by the amplifying unit, wherein the signal detected by the coordinate designating unit is a low impedance input circuit. The present invention proposes an information input device for amplifying by the amplifying section having the current-voltage converting means as described above.

[Operation] In the present invention, the impedance indicating circuit by the active element is not built in the coordinate pointing means, only the passive elements of the detection electrode and the switch circuit are built in, and the voltage amplification is not performed in the signal amplification section of the information input device body. Instead, a current-voltage conversion circuit that detects a current and converts it into a voltage is provided.

[Embodiment] The present invention will be described with reference to the accompanying drawings. FIG. 1 shows a block configuration. In the figure, reference numeral 1 is a tablet, and electrode lines are arranged at predetermined intervals in two orthogonal directions (X direction, Y direction) (not shown). Reference numeral 2 is a decoder driver, which sequentially applies scanning pulses to the above-mentioned electrode lines according to the address signal AD supplied from the central processing unit 3. The central processing unit is hereinafter referred to as "CPU", and in the following description, when other parts are abbreviated in parentheses after the names, the abbreviations will be used thereafter.

Reference numeral 4 is an input pen which is a coordinate indicating means, and reference numeral 5 is a detection electrode slidably held at its tip. Reference numeral 6 is a switch circuit, in which a plurality of switches are connected in parallel via resistors, and Vc is connected via resistors in the main body of the apparatus.
c It is pulled up to the power supply. One of the switches opens and closes in response to the sliding of the detection electrode 5. Reference numeral 7 is a current-voltage conversion circuit (IV conversion circuit) for converting the capacitance pulse induced in the detection electrode into a voltage. Reference numeral 8 in the low-pass removal filter, is for the noise caused by the vertical movement of the detection tip of the detecting electrode 5 is removed, and so as to remove the frequency components lower than 10KH _Z in this embodiment. Reference numeral 9 is a signal amplifier circuit which has a low impedance output. Reference numeral 10 is a sample hold circuit,
In response to a timing pulse TP supplied from the CPU 3 via the input / output port 12, the input voltage (electrostatic induction pulse voltage) at that time is held for a while. Reference numeral 11 is an analog-digital converter (AD converter) and has the same timing pulse.
In response to TP, the output voltage of the sample hold circuit 10 is digitally converted. The sample hold circuit 10 is for holding the electrostatic induction pulse voltage for the time required for the AD converter 11 to perform digital conversion.

The CPU 3 is a so-called microcomputer integrated into a circuit, and sends an address signal AD to the decoder driver 2 according to a program stored in the read-on memory (ROM) 13 to apply a scanning pulse to a predetermined electrode line of the tablet 1. At the same time, the sample and hold circuit 10 and AD converter
The timing pulse TP is supplied to 11, and the digital value of the induced pulse at this time is recorded in the RAM 14. Then, after performing this operation for all electrode lines or electrode lines in a predetermined range, coordinate data is calculated based on the magnitudes of the pulses.

In the present invention, the signal induced by capacitive coupling as shown in FIG. 2 is input not by the voltage but by the current. In FIG. 2, a general-purpose operational amplifier (OP amplifier) such as LM31 is used for the current-voltage conversion circuit (hereinafter referred to as IV conversion circuit).
The IV conversion circuit using 8 (manufactured by National Semiconductor), LF357 (manufactured by the same company), CA3100 (manufactured by RCA), CA3130 (manufactured by the same company), etc. is disclosed. The non-inverting terminal (+) has a zero potential (ground), and the inverting terminal (-) and the detection electrode 5 are connected by a cable. Since the point A of the OP amplifier has an imaginary short circuit with the point B, it has a zero potential, and the pulse current I induced in the detection electrode 5 is equivalent to being grounded via the cable. That is, the input impedance is 0
Ω, and ideally no current flows in the OP amplifier, and it appears as voltage V = −I · R at the point C through the resistor R. Since the input impedance can be made extremely low by IV conversion in this way, external noise is not picked up and it is less likely to be affected by the stray capacitance of the cable. Further, since the pulse current I induced in the detection electrode 5 is not influenced by the value of the feedback resistance R of the OP amplifier, a resistance value of several MΩ can be used for R and a high voltage margin can be secured.

[Advantages of the Invention] Since the present invention is configured as described above, it is possible to simplify and reduce the cost without requiring an impedance conversion circuit in the coordinate designating means, and between the device body and the coordinate designating means. The cable can also reduce the number of cores and improve operability.

[Brief description of drawings]

FIG. 1 is a block diagram of the present invention, FIG. 2 is an equivalent circuit diagram of the present invention, and FIG. 3 is a conventional equivalent circuit diagram. 1 ... Tablet, 2 ... Decoder driver, 3 ... CPU, 5 ... Detecting electrode, 6 ... Switch circuit, 7 ... Current-voltage conversion circuit, 10 ... Sample hold circuit

Claims (1)

[Scope of utility model registration request] 1. A tablet having a plurality of electrode lines arranged in a coordinate axis direction, a control unit for applying a scanning signal to the electrode lines of the tablet, and a scanning signal applied to the electrode lines of the tablet. A coordinate pointing means for capacitively detecting a signal to detect a signal, an amplification section for amplifying the signal detected by the coordinate pointing means, and a contact position of the coordinate pointing means with the tablet from the signal amplified by the amplification section. An information input device comprising a calculation unit for calculating, wherein the signal detected by the coordinate designating unit is amplified by the amplification unit having a current-voltage conversion unit as a low impedance input circuit.