JPH036609A - Acoustic coordinate input device - Google Patents

Abstract

PURPOSE:To attain a highly accurate digitizer system by securing a constitution where the output of a 1st comparator actuates a 2nd comparator not as a stop signal of a time counter circuit and the 2nd comparator is used as a zero- cross comparator. CONSTITUTION:The slice level is set high and low according to the value of the sound wave inputted not to a mere DC, e.g., an input pen is put close to or further away from a microphone respectively together with the waveform showing the output signal of a reference voltage correction circuit 110. The zero-cross comparators 113 and 114 (which detect the zero-cross points of the input sound wave signal undergone the waveform shaping) are set in the enable states to starts actions with the output signals of the comparators 111 and 112. Therefore both comparators 113 and 114 output the stop signals with high accuracy through the actions similar to those secured with the large amplitude when the circuit 110 outputs a slice level accordant with an input waveform. Accordingly, accurate and stable digitizer operation is executed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a surface input type acoustic coordinate input device (hereinafter referred to as a digitizer) that uses sound waves, and in particular, a device that outputs sound waves to determine coordinate positions. This invention relates to a circuit system that allows a specified input pen to stably input data anywhere on the digitizer surface.

[Conventional technology]

As computers have become more widespread, digitizers have played an important role along with keyboards as input devices. Recently, portable computers and notebook-sized word processors have been commercialized, and small digitizers have been incorporated as input devices. The sonic digitizer is suitable for being formed on a display panel because it has a simple structure and the input surface can be made of glass, plastic, etc.

An acoustic digitizer consists of a ben-type input ben that outputs intermittently emitted sound waves, and a main body that measures the spatial propagation time of the sound waves until they reach the receiving microphone of the digitizer body and reads the coordinates. This set of main bodies and input pens are synchronized with a time measurement circuit.

In other words, time measurement on the digitizer body side starts in synchronization with the output of sound waves from the input pen, and the time taken for the sound waves to reach the multiple receiving microphones on the digitizer body after a delay is measured, and the input pen Detect the coordinate position of. The synchronization signal that causes the start at this time is the same regardless of whether the input pen and digitizer are connected by wire, but if the input pen and digitizer are physically separated, Either one will issue a synchronization signal. In that case, there are various means of transmission, but radio waves and magnetism are usually used. Also, sound waves range from the audible band to several hundred KH2, such as ultrasonic waves, and are used at frequencies suitable for each system.

The operation of a conventional acoustic digitizer will be explained with reference to the drawings. FIG. 6 is a block diagram of a conventional acoustic digitizer. Reference numeral 601 is a timing circuit for intermittently generating sound waves, and at the same time is a synchronization signal generation circuit that is also a circuit for generating a start signal that serves as a reference for time measurement. An input pen 602 indicates input coordinates, and includes means for emitting sound waves in response to a synchronization signal, such as a piezoelectric speaker. 603 indicates the input surface of the digitizer.

604 and 605 are acoustic microphones for receiving sound waves from the input pen 602.

Reference numerals 606 and 607 are amplifier circuits that amplify minute signals from the microphone, and 608 and 609 are waveform shaping circuits that include bandpass filters and the like. Comparators 611 and 612 compare the received signal with a reference voltage VR. 610 is a slice level generation circuit that outputs a DC reference voltage VR.

616 is a time measurement circuit that stores a counter and its counter value (consists of a register, an interface circuit for exchanging data with the computer system, etc.), and measures the arrival time of the signals received from the two microphones. Each can be measured and the counter value can be read by a computer.

Now, if the speaker is an ultrasonic vibrator (for example, 40 KHz), a synchronization pulse is input from the synchronization signal generation circuit 601 to the speaker of Ben 602 electrically.

Then, the input pen 602 outputs a 40 KHz sound wave. At the same time, it instructs the time measurement circuit 616 to start measurement.

The sound wave propagates through the space above the input surface 606 and reaches the micro 04 and the micro 05 with a propagation time proportional to the position of the input pen 602, respectively. The sound wave that arrived is micro 0
After being converted into an electrical signal and shaped into a waveform by comparators 611 and 612, the reference voltage VR is detected as a slice level by comparators 611 and 612, and is converted into signals SL and SR for stopping the count of time measuring circuit 613.

The time to reach micro 04.605 is TL, respectively.
If TR, a corresponding counter value is set in the time measurement circuit 616. By reading this counter value, the computer can determine the two-dimensional position.
If necessary, it is easy to convert to orthogonal X-Y coordinates.

The rest can be handled in the same way as general mouse processing.

A specific circuit of the time measurement circuit 616 and its timing chart are shown in FIG. 6 (13) and FIG. 6 (Q).

620 is a counter that starts counting in response to a reset signal related to the synchronization signal. 621 and 622 are I10 registers that temporarily store the value of the counter 620, and are latched by the counter 620 at the timing when the value reaches the microphone. Also, L10 that can be read by the CPU system
It also serves as a port. 626 is comparator 611.6
12 output signals SL, SR and a synchronization signal, and also operates in conjunction with the CPU system 6140 control signal. For example, when the digitizer obtains data, it outputs an interrupt signal to the CPU or reads the status from the CPU.

Reference numeral 624 is an I10 port for interfacing the molding circuit 623 and the CPU system 614, and is herein referred to as a control register. Figure 6 shows a waveform diagram of the input and output of the comparator.

[Problem to be solved by the invention]

However, in conventional systems, if a high-Q characteristic such as an ultrasonic speaker is used for the output speaker of the input pen due to its efficiency, the output will resonate while it is being output.
The first few pulses have a small amplitude and therefore are shown in Figure 6 (D
As shown in the solid line waveform 640, for example, since the second pulse is sliced at the reference voltage VR (point A), the phase position of the sliced pulse is determined by the magnitude of the amplitude caused by the difference in the distance between the input pen and the microphone. This causes errors such as a deviation (point A → point B) and a deviation of one pulse (point A → point C), making it difficult to accurately read the distance between the microphone and the input pen, resulting in extremely poor accuracy. turn into.

In addition, in order to solve the former problem, the delay time TI of the rise when crossing the reference voltage VR as shown in Figure 6 (points A and D in D)
By measuring the fall delay time T2 and taking the average, it is possible to absorb some fluctuations in amplitude, but this requires two registers for each microphone, and a 16-bit counter, for example, is difficult to use due to system accuracy. If necessary, a 64-bit I10 register would be required, which is contrary to system simplification.

An object of the present invention is to provide a highly accurate digitizer system by eliminating the above-mentioned influence of part width and performing comparisons at a level that does not affect the influence of amplitude, even if there is some influence of amplitude.

[Means to solve the problem]

In order to achieve the above object, the present invention adds a correction circuit according to a function of the distance between the microphone and the input pen, and further provides a second comparator in addition to the conventional first comparator,
The output of the first comparator is not used as a stop signal for the time measurement circuit (it starts the operation of the second comparator, and the second comparator is configured as a zero-cross comparator. The reference voltage VR of the first comparator is corrected on the time axis according to the distance between each microphone on the main body and the input pen tip, or the gain of the input amplification of the microphone is controlled.The correction information is fixed according to the digitizer system. In some cases, the distance between the actual microphone and input pen can be controlled from the input amplitude read, and since most digitizers are used in combination with a CPU system, the input pen decoy read last time can be This configuration uses software to calculate corrections based on the distance between the microphone and the input pen, and feeds them back to the correction circuit.

[Example 1] Embodiments according to the present invention will be described based on the drawings.

FIG. 1 shows an embodiment in which a fixed reference voltage correction circuit is introduced in consideration of the relationship between the distance between the microphone and the input pen tip and the amplitude of the microphone output. 101 is a synchronization signal generation circuit, 102 is an input pen, 103.104 is a microphone, 105
．． Reference numeral 106 is an increaser circuit, 107 and 108 are waveform shaping circuits, and 109 is a time measurement circuit, as described in the prior art section.

Reference numeral 110 denotes a reference voltage correction circuit that also takes into consideration the correction of the output signal waveform of the waveform shaping circuits 107 and 108 and the distance between the microphone and the input pen. FIG. 1 (B is a waveform diagram of a typical signal, where waveform 123 shows the output signal of the reference voltage correction circuit 110, and due to the magnitude of the human-powered sound wave rather than a simple direct current, for example, when a human-powered pen is close to the microphone) The slice level is set high and becomes low when it is far away.111.
Reference numeral 112 denotes a converter which receives as input the waveform-shaped input sound signal and the reference voltage correction circuit output VREF.

Reference numerals 116 and 114 are zero loss converters for detecting zero crossing points of the waveform-shaped input sound wave signal, and are configured to be enabled and started to operate by the output signals of the comparators 111 and 112.

FIG. 1(C) is an embodiment of the reference voltage correction circuit 110 for obtaining the waveform 126 shown in FIG. 1(B). Ql and Q2 indicate PNP type transistors, and 130 is a comparator. Figure 1 (The pulse width TD of the current waveform 122 can be obtained from the time constant τ1 of the capacitor C1 and the resistor R1.1 Now, when the synchronization signal is applied to Ql, the output signal 121 will be ++ as shown in Figure 1 (B). At the same time as it is pulled to the side, discharge starts according to the time constant τ1.The output signal 122 is obtained by the comparator 160 which inputs this signal and the voltage ■1 obtained from the variable resistor VR.This delay time TD is the delay of the circuit in the digitizer system. The output signal 122 of the comparator 160 has a time constant determined by the capacitance C2 and the resistor R2 so that all stages operate at the same time. Create a signal waveform with τ.

This time constant τ exactly contributes to correcting the distance between the microphone and the input pen. This actual value should be optimized depending on your system configuration. Resistor R3 is the time constant τ of the VREF waveform 126.
This sets the voltage reached during exponential discharge due to
The voltage determined by the dividing wall of the resistor R2 and the resistor R3 becomes 0. The value of this voltage 0 is optimized in relation to system noise and the maximum distance between the microphone and the input pen. Reference voltage correction circuit 1 composed of the circuit shown in FIG. 1(C) above.
The output VREF of 10 serves as a reference voltage source for a comparator that takes into account the effects of the distance between the system, the microphone, and the input pen, as shown by waveform 126 in FIG. 1(B).

Next, the operation of the comparator will be explained using FIG. 1 (B). The comparators 111 and 112 in FIG.
and the waveform-shaped sound wave signal (i-shape 124). Conventionally, this comparator output (waveform 125) would be the stop signal for the time measurement circuit 1090 counting operation, but in the present invention, the second zero cross comparator 116.
Used as an enable signal for 4. Reference voltage correction circuit 1
10 can considerably remove the influence of amplitude, but there is a limit to completely removing phase errors. In order to realize a highly accurate digitizer, the present invention focuses on a zero-crossing point that does not have a phase error due to the magnitude of the amplitude, and uses a system that measures the time taken to reach this zero-crossing point. That is, the count stop signal to the time measuring circuit is generated at the first falling zero crossing point 0 at which the sound wave signal crosses the voltage O of the pulse detected by the pre-stage comparators 111 and 112. As a result, even if amplitude fluctuation occurs, it is absorbed by the pre-stage comparator, and the zero-weather comparator outputs highly accurate information. The waveform 125 in FIG. 1([3)] is the output of the pre-stage comparator, and is converted into a signal 126 by a similar circuit in FIG. 1(C). This signal turns on the operation of the zero cross comparator, and the output of the sono zero cross comparator becomes as shown in No. 127 of '8. When the input pen moves away from the microphone, Figure 1 (
Although the waveform becomes smaller as shown in B, in this system, since the reference voltage correction circuit 110 outputs a slice level that matches the input waveform, the zero cross comparators 113 and 114 can accurately generate the stop signal by the same operation as when the amplitude is large. (waveform 127), and eventually achieves accurate and stable digitizer operation.

[Example 2] In Example 1, a fixed correction was applied to the reference voltage correction circuit to suit the system, whereas in Example 2, the input amplitude at one sampling time is fed back to the reference voltage at the immediately following sampling time. It is.

Since the sampling frequency of the digitizer is usually high enough relative to the movement of the input pen, the positions of the front and rear input pens do not change significantly. Therefore, by always creating a reference voltage based on the amplitude information of the previous sampling, the microphone and input The distance to the pen can always be adjusted optimally. Figure 2 (/
', ) shows the block diagram. The main circuit blocks operate in the same manner as in the first embodiment, so their explanation will be omitted. However, reference voltage correction circuits 201 and 202 exist for each microphone,
These input signals include not only the synchronization signal but also the output signals of the waveform shaping circuits 107 and 108, and the reference voltage V RE F for the next measurement is created based on the peak voltage. Therefore, the two voltages VREF differ depending on the position of the input pen, and are voltages related to the distance between each microphone and the input pen. FIG. 2(B) shows one embodiment of the reference voltage correction circuits 201 and 202, and FIG. 2(C) shows its operating waveforms. 22
0 is a peak hold circuit, which in this system outputs the peak voltage ■P of the waveform-shaped sound wave input. A synchronous signal is used for each clear signal. 221 is an amplifier circuit whose gain is approximately C1.7 based on experience, and converts the peak hold circuit output VP into the amplifier circuit output VREFO. 222
is a frequency divider that divides the frequency of the synchronizing signal into 1/2, and its output controls a switching circuit composed of switches 226, 224, 225, and 226. By this switch operation, the reference voltage VREF outputs a voltage predicted by the previous sound wave amplitude of the sound wave signal to be measured, and the comparator 111.1
It is input as 12 reference voltages. The main waveforms at this time are shown in FIG. 2(C). The operation of the entire digitizer system is similar to that of the first embodiment.

Although the number of circuit blocks is increased compared to the first embodiment, it is effective because there are fewer constant settings.

[Embodiment 3] In Embodiment 1.2, the reference voltage correction circuit was configured independently of the CPU system, whereas in Embodiment 3, the digitizer is usually used in conjunction with the CPU system, so This is an example in which the CPU system is effectively utilized. In this case, the CPU system can be considered in two ways: one is the main CPU of the computer, and the other is a CPU system that exists in a digitizer system separate from the computer.

FIG. 3 is a block diagram of the third embodiment.

301 and 302 are reference voltage correction circuits that create a reference voltage VREF. This reference voltage correction circuit 601.602
is an analog/digital converter whose input signal is a bit input.
The reference voltage V RE and F can be controlled by the CPU system. 303 and 304 are C
This is an input/output interface circuit that connects the PU system and the reference voltage correction circuit, and is generally called an I/O port that is made up of registers and the like. In the second embodiment, the information for creating the reference voltage was obtained from the amplitude of the sound wave signal, whereas in this embodiment, the position of the input pen is calculated by the CPU system, so the result is used instead. However, this method digitally corrects the reference voltage according to the distance between the microphone and the input pen each time.

Although it takes more time to calculate the digitizer of the CPU, it is characterized by requiring less circuitry.

Further, if software correction is to be avoided, the digital bit information of the reference voltage correction circuits 601 and 602 may be provided by the counter output of the time measurement circuit 109. FIG. 3 shows the main waveforms of the third embodiment.The operation of the entire digitizer system other than the reference voltage correction circuit is the same as that of the first embodiment.

[Example 4] As another method of correcting the amplitude due to the distance between the microphone and the input pen using the CPU system, an example is shown in which a programmable amplifier circuit is provided in place of the simple amplifier circuits 105 and 106. It is shown in Figure 4. Reference numeral 610 is a slice level generation circuit that generates a conventional simple DC level reference voltage VR, and 303 and 304 are input/output interface circuits described in the third embodiment. 401 and 402 are programmable amplifier circuits whose gains can be digitally controlled. The operation is the same as in Example 3, and C
This is a method in which correction information calculated by the PU system is fed back to the programmable amplifiers 401 and 402 instead of to the reference voltage correction circuit. A simple waveform diagram is shown in FIG. 4 (B).

[Embodiment 5] In the present invention, the digitizer body including the MyFake and the input pen are both wired and wirelessly connected, but in reality, they are connected wirelessly after use. This is desirable. In that case, the problem is the means for transmitting the synchronization signal.Finally, in the case of a wireless system, an input Ben system using magnetism as the means for transmitting the synchronization signal is shown as an example in FIG.

Reference numeral 501 denotes a timing generation circuit within the input pen that includes a reference oscillator, and generates pulses for outputting synchronization signals and sound wave signals. From the propagation speed of the sound wave in space, the coordinate calculation time, and the maximum movement speed of the input pen, the intermittent frequency of the sound wave and the synchronization signal is 100 [z ~ several hundred Hz. 502 is the input pen state detection circuit Using a mouse as an analogy, it detects whether or not it is clicked and modulates it into a synchronization signal.For example, if the synchronization signal is normally 200 Hz, the frequency of the click is 400 Hz.
Let it be Hz.

506 is a coil amplifier circuit that drives the coil 504 installed at the tip of the input vent. Reference numeral 505 is a speaker drive circuit for a speaker 506 that outputs sound waves. For example, when an ultrasonic vibrator is used in the speaker, a thin pulse of several tens of volts is generated to drive the ultra-We speaker (of course, basically The synchronization signal and the sound wave are guided to the magnetic detection circuit and the sound wave detection circuit of the digitizer body, and measurement starts.For magnetic detection, for example, a flat coil 510 is provided on the surface of the digitizer body.
A synchronization signal can be obtained by detecting the current caused by magnetic changes. 511 is an amplifier circuit for magnetic detection, 512 is a waveform shaping circuit including a noise removal filter, etc.
Outputs a signal equivalent to the synchronization signal explained in . Although all embodiments of the present invention have been described with a configuration having two receiving sections, the present invention is not limited thereto.

〔Effect of the invention〕

The present invention has been described in detail above, but the basic configuration of the present invention is a correction circuit for minimizing the influence of input amplitude, a first comparator, and a second comparator controlled by the first comparator. By combining it with a zero-loss comparator, measurement errors can be minimized because it is not affected by the size of the sound waves that reach the microphone, making it possible to achieve a stable high-resolution digitizer.

[Brief explanation of drawings]

The first arrangement is a professional drawing of Example 1 according to the present invention, and the first
Figure (B) is a waveform diagram of Example 10, Figure 1 (C) is a circuit diagram of the reference voltage correction circuit of the first position, Figure 2 (A) is a block diagram of Example 2 according to the present invention, (output) is a circuit diagram of the reference voltage correction circuit of (second recovery), FIG. 2(C) is a main waveform diagram of the second embodiment, and third device is a block diagram of the third embodiment of the present invention. (B) is its main waveform diagram, the fourth device is a block diagram of the fourth embodiment of the present invention, FIG. 4(B) is its main waveform diagram, FIG. 5 is a block diagram of the input pen system, and FIG. Figure 6(CB) is a block diagram of the original system, Figure 6(CB) is a circuit diagram of the time measurement circuit of Figure 6(A), Figure 6(C) is a waveform diagram of the conventional system, Figure 6(D) is an operation waveform diagram of the comparator. 111.112...Comparator, 113.1
14...Zero cross comparator, 110.20
1.202.301.602...Reference voltage correction circuit, 401.402...Programmable amplifier circuit. Book 2 noon (C) Fig. 4 01 (A) (B) Fig. 5 Fig. 6 (C) G liquid signal

Claims (6)

[Claims] (1) At least an input pen that emits sound waves, two or more microphones and a receiving circuit that receive the sound waves, and a comparator that compares the output signal of the receiving circuit with a reference voltage;
In the acoustic coordinate input device comprising the comparator output and a time measurement circuit that detects the propagation time of the sound wave using a synchronization signal synchronized with the sound wave, the comparator is divided into a first comparator and a second comparator; The first comparator outputs a signal that allows the operation of the second comparator by comparing the output signal of the receiving circuit with the reference voltage, and the second comparator operates according to the first comparator output signal, and the output signal of the receiving circuit is zero An acoustic coordinate input device characterized by being a cross comparator. (2) The reference voltage input of the first comparator is connected to a reference voltage correction circuit that synchronizes with the synchronization signal and outputs a voltage according to the distance between the microphone and the input pen on the time axis. 1. The acoustic coordinate input device according to 1. (3) The reference voltage correction circuit determines the time until the output signal begins to fall exponentially using a time constant determined by the first capacitance and resistance with reference to the synchronization signal, and the time constant determined by the first capacitance and resistance. 3. The acoustic coordinate input device according to claim 2, wherein a falling time constant of the output signal is determined by a third resistor, and a voltage reaching an exponential value is determined by a third resistor. (4) The reference voltage correction circuit consists of a peak hold circuit that receives the output of each receiving circuit as an input, an amplifier with a gain of 1 or less connected to the output of the peak hold circuit, and an output that switches between the amplifier outputs every cycle of the synchronization signal. 3. The acoustic coordinate input device according to claim 2, wherein the acoustic coordinate input device comprises a switch circuit that corresponds to each receiving circuit. (5) A claim characterized in that the reference voltage correction circuit is composed of a digital converter whose input is the output of an I/O port connected to the CPU system, and is provided correspondingly to each receiving circuit. Item 2. The acoustic coordinate input device according to item 2. (6) Each receiving circuit is connected to the CPU system.
2. The acoustic coordinate input device according to claim 1, further comprising a programmable amplifier whose input is the output of the O port.