JPH0149971B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a coordinate input device used for inputting coordinate information required in CAD and the like.

(Conventional technology) Conventionally, the configuration shown in FIG. 2 has been used.

A clock signal generated by the CPU is supplied to the coil unit 21 via an AC generating circuit 23 and a driving circuit 22, and an AC magnetic field is generated from the coil unit.

This signal is generated by the sense line 1, which is formed by arranging a large number of coils with one turn each in the X and Y directions.
3, and a voltage is induced in the sense line coil.

This sense line coil is controlled by the CPU via a multiplexer circuit 14, and the arrayed coils are sequentially detected. The CPU can determine the coordinate position of the pen tip by detecting the voltage-induced location.

For this purpose, the signal induced in the sense line coil is amplified by an amplifier circuit 15 in order to amplify only the AC signal driving the coil section 21, and then frequency noise other than the drive signal is removed by a bandpass filter 16. do. The pen drive AC signal component passes through a detection circuit 17 and an integration circuit 18 with a low-pass filter function, and is converted into a digital signal by an A/D conversion circuit 19 in order to detect a peak value and perform arithmetic processing on its height. Arithmetic processing is performed by the CPU 20.

The oscillation circuit 24 generally uses a crystal,
In addition to supplying the clock signal for the CPU 20,
It is also used as a clock for the timer circuit built into the CPU, and serves as a reference signal for generating alternating current signals.

The results of the arithmetic processing performed by the CPU 20 are output as coordinate values.

(Problems to be Solved by the Invention) In the conventional system, the sense line works as an antenna for minute noise, so the characteristics of the bandpass filter are important for stable operation.
Since a device with small transient response and sharp cutoff characteristics is required, adjustment is complicated, the shape is large, and it is disadvantageous in terms of cost.

Therefore, the present invention provides a detection method that eliminates this bandpass filter and provides an even better S/N ratio.

(Means for solving the problem) In order to perform detection with a good S/N ratio, the present invention uses a multiplier or an analog switch in the detection circuit, and selectively detects only the driven AC signal component. was removed.

(Operation) FIG. 3 shows waveforms of main parts in the present invention. P is a waveform when only the pen drive AC signal is output to the amplifier circuit 3 of FIG. 1, which is a block diagram of the present invention. q is a signal whose phase is shifted by the phase shift circuit 11 in order to make the AC generation signal generated by the CPU have the same phase as the P signal. When the signal P and the signal q are input to a multiplier, the output signal of the multiplier has the waveform of the signal r and becomes the detected output.

Also, the same effect can be achieved by turning on/off an analog switch using the signal q instead of this multiplier.

By integrating this signal r by the integrating circuit 18, it becomes possible to obtain the strength of the electromagnetic coupling strength as an output signal.

Here, when the signal P is noise other than the drive frequency component, the output r of the detection circuit is output in both positive and negative directions, and the integral value becomes zero, and the output r is outputted in both positive and negative directions. Noise can be removed by Further, the result of integrating the output of the integrator with respect to signals other than signals synchronized with signal q becomes zero, and the influence can be ignored.

(Example) FIG. 1 is a block diagram of the present invention, and FIG. 5 is a detailed diagram thereof.

The reference signal generated by the oscillation circuit 12 is the CPU
7 as a clock signal, and also generates a reference signal necessary for driving the coil by means of a built-in timer circuit.

This signal is used as a clock signal for the phase shift circuit 11 and is also input to the AC generating circuit 10. This AC generating circuit synthesizes two-phase signals to drive the coil. The two-phase signal is input to two amplifiers that constitute the drive circuit 9, and the coil 8
is driven by AC. The magnetic flux generated by the coil 8 induces a voltage in a sense line in which a large number of one-turn coils are arranged in the X and Y directions. The CPU 7 can know the position of the coil 8 by detecting which sense line is driven to induce the maximum voltage.

The voltage generated on the sense line 1 is amplified by an amplifier 3 and input to a detector 4, which is a feature of the present invention. A phase shift circuit 11 generates a signal that is completely synchronized with the detection signal, and a multiplier or an analog switch. Phase detection is performed by the configured detection circuit 4.

This phase detection detected signal is integrated. At this time, all components other than the noise component and the drive signal are averaged, resulting in an atmosphere signal. Therefore, the strength of the coil drive signal component becomes the output signal of the integrating circuit 18.

This signal is digitally converted by the A/D conversion circuit 6, processed by the CPU 7, and used to detect the position of the coil.

Next, from the reference signal output from CPU7,
The main waveforms until input to the A/D conversion circuit 19 are shown in FIG. 4, and the detailed circuit is shown in FIG. 5.

A 1228.8 KHz clock is input from the CPU 7 to the flip-flop 25 in FIG. Therefore flip-flop 2
Output a of 5 is 614.4KHz, flip-flop 26
The output b is a square wave output of 307.2KHz.

The output a of the flip-flop 25 and the output b of the flip-flop 26 are input to the AND gate 27, and the output waveform becomes the waveform C shown in FIG.

Similarly, the waveform a and the negative output of the flip-flop 26 are input to the AND gate 28, and the output becomes as shown in FIG. 4d. C and d in FIG. 4 are two-phase signals for generating alternating current, and these signals are input to buffers 29 and 30 for driving the coils.

A waveform ef shown in FIG. 4 is applied to both ends of the coil 31, and an alternating current of 307.2 KHz flows through the coil. The value of capacitor 32 is
In combination with 1, the resonant frequency is set to 307.2KHz and harmonics are cut.

As a result, the coil 31 is driven with a waveform very close to a sine wave.

When the coil 31 is brought close to the sense line 38,
CPU controlled multiplexer 39
A voltage is induced in the coil array of the scanned turn by a and 39b.

This signal is amplified by an amplifier 34 and then input to an analog switch 35. At this time, if noise is ignored, the waveform g shown in FIG. 4 is input.

The analog switch 35 is controlled by the signal h synchronized with the waveform g by the shift register 33. Therefore, the output of the analog switch 39 has a waveform like c in FIG. By passing this waveform through an integrating circuit constituted by a combination of an amplifier circuit 36 and a capacitor 37, a voltage proportional to the voltage intensity generated on the sense line can be obtained.

Since the A/D converter, oscillation circuit, and CPU are generally well-known circuits, their explanations will be omitted.

The coil part is usually a pen with a coil embedded in the tip, or a cursor is often used.

Also, in principle, a magnetic field is generated on the sense line side,
It is also possible to detect it in the coil section, and the operation is equivalent.

The signals processed by the CPU are output as coordinate values to each connected device.

In the description of the present invention, the bandpass filter is removed, but even if it is connected in the conventional manner, the effects of the present invention are not impaired in any way, and it is even more effective when performing highly accurate detection. Even in this case, the required characteristics of the filter are significantly relaxed compared to conventional filters.

(Effects of the invention) By using phase detection detection, it is possible to eliminate the need for coils and adjustment points, and furthermore, it is possible to configure the detection section entirely with circuit elements that can be easily integrated into ICs. space saving, cost reduction,
The effects of high-sensitivity detection, such as significant performance improvement, are significant.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of this invention.
Fig. 2 is a block diagram of a conventional example, Fig. 3 is a waveform diagram regarding detection of the present invention, Fig. 4 is a waveform diagram of the circuit example shown in Fig. 5, and Fig. 5 is a circuit diagram of an embodiment of the present invention. . 1... sense line, 3... amplifier, 4... detection circuit, 5... integrating circuit, 8... coil, 11... phase shift circuit, 7... CPU.

Claims (1)

[Scope of Claims] 1. A moving coil that generates an alternating magnetic field, a sense line arranged in the X and Y directions to detect the position where the magnetic field is generated, a multiplexer that scans the sense line, and the moving coil. The detection circuit has the function of a low-pass filter, an amplification section that amplifies the detection signal induced in the sense line by the amplification section, and a multiplier circuit that detects the detection signal amplified by the amplification section. In a device consisting of an integrating circuit that integrates a signal, an AD converter that converts the signal from the integrating circuit into an AD converter, and a processor section that processes these signals, the detection circuit is used to drive the moving coil section. An electromagnetic coupling type coordinate input device characterized in that detection is performed by turning on/off the detection signal with a signal having the same frequency as an alternating current signal. 2. An electromagnetic coupling type coordinate input device according to claim 1, characterized in that the detection circuit is constituted by an analog switch.