JPH086704A - Noise removing circuit of ultrasonic coordinate detecting device - Google Patents

Abstract

PURPOSE:To obtain a small-sized digitizer which can suppress external noises other than a specific ultrasonic wave signal for coordinate detection and discriminate whether a detected ultrasonic wave signal is normal or a noise. CONSTITUTION:The coordinate detecting device consists of a coil 1 which detects an electromagnetic wave signal from a coordinate indicator and generates a synchronizing signal from this detected signal, a resonance circuit 2, an amplifying circuit 3 and a pulse shaping circuit 4, a microphone 8 which detects the ultrasonic wave signal from the coordinate indicator, an amplifying circuit 9, a band-pass filter 10, a comparator 11 and a waveform detecting circuit 12, an oscillation circuit 5 for detecting the delay time of the synchronizing signal up to the ultrasonic wave signal detection, a counter 6, and a latch 13. Then a threshold value signal generating circuit 7 which generates a threshold value signal of the comparator 11 by using the synchronizing signal is provided between the pulse shaping circuit 4 and comparator 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise detection / elimination circuit in an ultrasonic type coordinate detection device.

[0002]

2. Description of the Related Art Conventionally, an ultrasonic method, an electromagnetic induction method, a magnetostriction transmission method, a capacitance coupling method, etc. are generally known as a coordinate detecting apparatus using a cordless coordinate indicator.

Above all, since the coordinate detecting apparatus adopting the ultrasonic method is apt to erroneously recognize the coordinate detection position due to noise, conventionally, a special ultrasonic microphone is used to suppress the influence of external noise, or considerably. Various efforts have been made to remove defective coordinate information generated by noise by providing a steep filter after the microphone amplifier or by estimating the coordinate position by software.

[0004]

In a cordless coordinate detection device using ultrasonic waves, noise from the outside is a major factor in erroneously recognizing the coordinate detection position by the coordinate indicator. Therefore, how to suppress external noise in the coordinate detection circuit or how to distinguish noise information from normal information has been a major issue.

In the prior art, as a means for solving the above problems, a special microphone, a steep filter circuit or the like is required as described above, and as a result, it is difficult to miniaturize a portable device or the like incorporating the coordinate input device. there were. An object of the present invention is to solve the above problems and to provide a special component without
An object of the present invention is to obtain a small-sized coordinate detection device that can extract only desired coordinate indication signals from detected ultrasonic signals.

[0006]

SUMMARY OF THE INVENTION The present invention comprises a stylus pen that periodically generates a coil synchronizing signal and an ultrasonic signal at the same timing for each pulse, and a means for detecting the synchronizing signal and the ultrasonic signal. The synchronization signal is used as a reference signal, and an accurate coordinate position is detected by an ultrasonic signal that arrives after a delay.

Further, in order to accurately detect the coordinate position, the coordinate detecting device utilizes that the ultrasonic waveform is an AC waveform, and after the waveform once exceeds a predetermined threshold value,
The coordinate position is detected by the ultrasonic signal by detecting the first zero cross. Normally, the ultrasonic signal decays exponentially as the distance from the stylus pen to the microphone increases.

According to the present invention, means for causing the threshold to move in the same manner as the exponential function is added to the coordinate detecting device, and as a result, erroneous recognition of the coordinate signal due to external noise is suppressed. It was done like this. The detection area of the coordinate detecting device for the synchronization signal is determined by the inner diameter of the coil wound inside the coordinate detecting device, and the sampling cycle of the stylus pen is about 100 pps, that is, the sampling interval is 10 msec.

On the other hand, since the speed of sound waves is about 330 m / sec, for example, in the case of a coordinate detecting device of 50 cm square,
The maximum digitizing area distance from the microphone is 50 cm x 1.
41 = 71 cm, 0.71 ÷ 330 = in time
It is 2.2 msec, and the remaining 80% of the sampling period is a period unnecessary for coordinate detection.

According to the present invention, by providing a detecting means for detecting an ultrasonic wave signal in this section, it is possible to identify whether the obtained information is a predetermined coordinate position signal or noise. is there.

[0011]

In the present invention, the synchronizing signal by the electromagnetic wave serves as a reference for the distance measurement with respect to the ultrasonic wave oscillation source, that is, the coordinate 1, and the reference signal is periodically generated in every constant section.

On the other hand, the coordinate position is determined by measuring the delay time until the arrival of the ultrasonic signal with respect to the input synchronization signal, and the measurement is ended once the ultrasonic signal has reached a predetermined threshold value TH. It is the first zero-cross point after crossing.
Further, the ultrasonic signal has a different amplitude depending on the delay time with respect to the synchronization signal, but in order to remove external noise and detect only the ultrasonic signal, the threshold value for the ultrasonic signal is set as high as possible. It is desirable to set.

That is, the disturbance of the amplitude due to the external noise component is set to be equal to or less than the threshold value in order to cut these noises. Therefore, in the present invention, the threshold value is changed in accordance with the ultrasonic signal so that the maximum threshold value is always obtained when the ultrasonic signal is detected.

Further, a noise detection section is provided in the latter half of the sampling section outside the coordinate detection area, the ultrasonic signal is re-detected in the noise detection section, and it is discriminated whether the obtained information is a coordinate signal or a noise signal. It was made possible.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a functional block diagram showing an embodiment of the present invention. An electromagnetic wave signal generated from a stylus pen (not shown) serves as a reference signal for coordinate detection by ultrasonic waves, and this electromagnetic wave signal is detected by the resonance circuit 2 via the coil 1 provided on the coordinate detecting device side. , The signal detected through the amplifier circuit 3 is amplified. After that, the signal output from the amplifier circuit is input to the pulse generation circuit 4,
In the pulse shaping circuit 4, the sync signal CL is generated based on the input signal.
Generate RCNT and PSOUT. On the other hand, the digital clock signal PCLK is generated by the oscillation circuit 5 and supplied to all digital circuits of the pulse shaping circuit 4, the counter 6, the waveform detection circuit 12, and the noise detection circuit 14.

The synchronization signal CLRCNT is one clock width of the clock signal PCLK, and the synchronization signal PSOUT is
The pulse is about 1 μm. In addition, the all-digital circuit is initialized with a synchronization signal CLRCNT. Further, the counter 6 that measures the distance from the ultrasonic signal oscillation source is C
It is reset by LRCNT and counted by the clock signal PCLK.

Next, an ultrasonic signal generated by a stylus pen (not shown) is a signal for detecting a coordinate position,
First, it is detected by the microphone 8, passes through the amplification circuit 9 and the bandpass filter 10, and becomes an ultrasonic signal SOUND, which is input to the comparator 11. On the other hand, the threshold signal generation circuit 7 uses the synchronization signal PSOUT to generate a threshold signal TH that decays exponentially.

In the comparator 11, the ultrasonic signal SOUND and the threshold signal TH output from the threshold signal generating circuit 7 are input and then compared, and the ultrasonic signal SOUND is equal to or higher than the threshold signal TH. In case of "High" PTI
The signal and the PZI signal that is “High” when the ultrasonic signal SOUND is equal to or lower than the reference potential are generated by comparing with the reference potential.

Further, the waveform detection circuit 12 to which the PTI signal and the PZI signal are input, generates an ultrasonic wave detection signal PLD. On the other hand, the data of the counter 6 is stored in the latch 13 by using the ultrasonic detection signal PLD generated by the waveform detection circuit 12 as a trigger, and the measurement of the distance is completed.

Further, the noise detection circuit 14 generates a BLANK signal indicating a noise detection section of "High" at a suitable timing of the counter 6 and a signal RSNF signal for resetting the ultrasonic detection circuit, and outputs the BLANK signal. If an ultrasonic signal is detected later, it is set to “High” N
Generate an OI signal.

FIG. 3 shows an example of a specific circuit of the threshold signal generating circuit 7, which will be described below. The synchronization signal PSOUT output from the pulse generation circuit is a pulse that becomes “Low” for about 1 μsec, and is the synchronization signal PSOU.
T is a PNP transistor Q via a current limiting resistor Rc.
When the threshold signal is "Low", Q is turned on and the threshold signal TH becomes Vc.

When the PNP transistor Q is turned off, the P
Since the electric charge of the capacitor Ca stored when the NP transistor Q is on is discharged through the resistors Ra and Rb, the threshold value TH is exponentially attenuated to a potential of Vc × {Rb ÷ (Ra + Rb)}. . FIG. 4 shows an example of specific circuits of the comparator 11, the waveform detection circuit 12, and the noise detection circuit 14.

The ultrasonic signal SOUND is sent to the comparator 4
At 01, it is compared with the threshold signal TH to generate a PTI signal, and at the same time, the comparator 402 is compared with a reference potential to generate a PZI signal. The PTI signal and the PTZ signal are the D-FF 403 and 405 and the RS-FF 404.
At, the PLD signal is generated by the PZI signal after outputting the PTI signal.

Further, the arbitrary data PDATx of the counter 6
Is connected to the D-FF 409 via the OR 408,
After PDATx is "High", it is held until the signal CLRCNT from the pulse forming circuit becomes "High", and in the subsequent D-FF410, BLANK indicating a noise detection section.
Generate a signal.

Q output of D-FF410 and D-FF409
The Q output of is connected to AND 407 and produces an RSNF signal indicating the rising edge of the BLANK signal. The RSNF signal is connected to the reset of each FF 403, 404, 405 via the OR 406 to enable ultrasonic detection even during the output of the BLANK signal which is the noise detection section signal, and the PLD is generated when the BLANK signal is "High". Then, the D-LT 411 holds the state as the NOI signal, and identifies the presence or absence of noise.

[0026]

As described above, in the present invention, the influence of external noise can be suppressed and smooth coordinate detection can be performed without using a microphone or a filter circuit having a sharp frequency characteristic as in the prior art. Become.

Since no special circuits or parts are required,
The circuit can be downsized, and an ultrasonic coordinate detecting device for a small portable device can be realized.

[Brief description of drawings]

FIG. 1 is a waveform explanatory diagram of the present invention.

FIG. 2 is a functional block diagram showing an embodiment of the present invention.

FIG. 3 is a circuit diagram of a threshold signal generation circuit according to the present invention.

FIG. 4 is a circuit diagram of a comparator, an ultrasonic wave detection circuit, and a noise detection circuit of the present invention.

[Explanation of symbols]

 1 Coil 2 Resonance Circuit 3 Amplifying Circuit 4 Pulse Shaping Circuit 5 Oscillation Circuit 6 Counter 7 Threshold Signal Generation Circuit 8 Microphone 10 Bandpass Filter 11 Comparator 12 Waveform Detection Circuit 13 Latch 14 Noise Detection Circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhisa Hasunuma 6-31-1, Kameido, Koto-ku, Tokyo Seiko Electronics Industry Co., Ltd.

Claims (2)

[Claims] 1. An electromagnetic wave signal from a coordinate indicator is detected,
A coil for generating a synchronization signal from this detection signal, a resonance circuit, an amplification circuit and a pulse shaping circuit, and a microphone for detecting the ultrasonic signal from the coordinate indicator,
A coordinate detection device comprising an amplification circuit, a bandpass filter, a comparator and a waveform detection circuit, and an oscillation circuit for detecting the delay time until the ultrasonic signal is detected with respect to the synchronization signal, a counter, and a latch, wherein the pulse A noise eliminating circuit in an ultrasonic coordinate detecting apparatus, characterized in that a threshold signal generating circuit for generating a threshold signal of the comparator is provided between the shaping circuit and the comparator by using the synchronizing signal. 2. A noise detecting circuit for detecting noise in a section corresponding to the outside of the digitizing area by using a signal from the counter between the counter and the waveform detecting circuit. Noise removal circuit in acoustic wave coordinate detection device.