JPH07271496A - Signal pen circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] This is a signal pen circuit without a cable of the mutual inductance coupling type coordinate detection device, which has high output and low power consumption, a constant output level even if frequency is shifted, and high electrical operation. Reliable, low cost, lightweight signal pen. [Structure] An output tank circuit, a C-class operation transistor for driving the tap on the way, a Schottky barrier diode connected from the base of the transistor toward the collector, and an unadjusted oscillation connection via a drive resistor. It is mainly composed of a ceramic oscillator, an oscillation frequency shifting capacitor, and a power supply unit. [Effect] It is possible to operate with a power consumption of 55 μA from one battery of 1.55 V, and the above-mentioned objects are completely satisfied by a simple circuit configuration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coordinate pointing signal pen without a cable that abuts a tablet of a mutual inductance coupling type coordinate detecting device.

[0002]

2. Description of the Related Art As a circuit used for a conventional coordinate pointing signal pen without a cable, a parallel resonant circuit including a transmission output coil and a capacitor is oscillated by a CMOS inverter and a resistor is used by the signal. Driving circuits are known. There is also known a circuit for driving a series resonance circuit including a transmission output coil and a capacitor via a resistor by the oscillation voltage of the CMOS inverter. Further, a circuit is known in which a rectangular wave generation voltage of an oscillator is applied to a transmission coil via a resistor without forming a resonance circuit. It is easily conceivable that the coils of the Pierce BE circuit and the Pierce CB circuit using a crystal oscillator or a ceramic oscillator as a general oscillation circuit can be used as the transmission coil.

[0003]

The conventional signal pen uses three or more batteries to obtain a large signal current. Also, since the power supply current is large and 200 μA or more flows, the battery life is short and the replacement cost is high. Since a large amount of batteries are used, the weight of the signal pen is heavy, and in particular, a female operator has demanded a lightweight signal pen. Further, the Pierce BE circuit and the Pierce CB circuit had large errors in the oscillation frequency.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. In the mutual inductance coupling type coordinate detecting device, a coordinate indication without a cable that abuts a tablet having a grid loop electrode wire. A signal pen circuit for use in a signal pen, the output tank circuit comprising a resonance type transmission coil and a resonance capacitor at the tip of the signal pen for mutual inductance coupling with the loop electrode wire of the tablet, and a collector current of the transmission coil. A class-C operation transistor that drives a tap on the way, a Schottky barrier diode connected from the base of the transistor toward the collector, and a collector of the transistor
A signal pen circuit comprising: a ceramic oscillator connected between the bases through a drive resistor on the collector side without adjustment and oscillation; and an oscillation frequency shifting capacitor that can be connected to and separated from the ceramic oscillator in parallel. Is proposed.

[0005]

[Operation] Part of the electric vibrations stored in the output tank circuit (parallel resonance circuit consisting of coil and capacitor) is applied to the ceramic vibrator, and the inverted phase vibration voltage of the natural vibration frequency of this ceramic vibrator is used only in this circuit. It is fed back to the base of the transistor which is an active element of, and the transistor is operated in class C. The collector of the transistor drives the intermediate tap of the coil of the output tank circuit, but since it is a class C operation, the output tank circuit can be driven very efficiently. A high oscillating current flows between both ends of the output tank circuit due to a voltage higher than the tap in the middle. Also, since the Schottky barrier diode is mounted from the base of the transistor to the collector, automatic adjustment of the base drive DC level works,
Even if the hFE of the transistor is varied, the ceramic oscillator is slightly shifted in frequency, the resonance frequency of the output tank circuit is slightly different, or the coupling coefficient with the loop electrode wire of the tablet is changed. , The output voltage is kept almost constant. Furthermore, since a part of the reactance component of the output tank circuit is combined with the reactance component of the ceramic oscillator, the frequency error of the ceramic oscillator is corrected by finely adjusting the resonance frequency of the output tank circuit.

[0006]

The details of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall configuration diagram of a mutual inductance coupling type coordinate detecting device using the present signal pen. An AC signal generator 1 of an active circuit is arranged inside the signal pen 4 to generate a continuous AC signal and apply it to the transmission coil 3 at the tip of the signal pen. A battery 2 as a power supply unit supplies operating power to a circuit inside the pen.

When the transmitting coil 3 at the tip of the signal pen 4 is near the board surface of the tablet 6, the transmitting coil 3 and the respective loop electrode wires 7, 7, 7, ... Of the tablet 6 are mutually inductance-coupled. Therefore, the electric signal flowing through the transmission coil 3 at the tip of the signal pen 4 is transmitted to the respective loop electrode wires 7, 7, ... Of the tablet 6 at a level according to the magnitude of the coupling coefficient. The X-direction and Y-direction analog multiplexers 8 and 9 sequentially switch the signals received by the respective loop electrode lines 7, 7, 7, ... And apply them to the resonance transformer 10. The X direction and the Y direction operate in a time division manner. For example, when the X direction analog multiplexer 8 selects any loop electrode line 7, the Y direction analog multiplexer 9
Is off.

The resonance transformer 10 functions as a bandpass filter, and effectively passes only signals in a required frequency band.
The electric signal that has passed through the resonance transformer is amplified by the amplifier 11 to a voltage level sufficient for measurement, and the frequency is measured by the controller 13 and the voltage level is measured by the signal level detector 12.

Regarding this voltage level measurement and coordinate determination,
It will be described briefly as it is related to the required characteristics of the signal pen. The reception level of each loop electrode wire 7, 7, 7, ... On the tablet 6 is measured, but the signal at, for example, the X-axis position (also for the Y-axis position) on the tablet 6 is measured. Pen 4
The signal level of the loop electrode wire 7 closest to the tip end of the signal pen 4 is highest, and the signal pen 4 is calculated or calculated from three levels including the signal levels of the loop electrode wires 7 and 7 before and after that.
The coordinates are determined by interpolating the precise position of the tip of the. Therefore, even if the analog multiplexers 8 and 9 are switched so that the mutual inductance coupling coefficient changes (the load of the signal pen 4 slightly changes), the output level of the transmission coil 3 needs to be maintained at a constant level. If the output fluctuates, accurate coordinate determination cannot be performed.

A signal pen circuit that meets the above-mentioned conditions will be described below. FIG. 2 shows the entire circuit of the signal pen 4 powered by one silver oxide button battery. A battery 36 of approximately 1.55V supplies the operating power for this circuit. The resistor 38 is for preventing surge current (for example, 100Ω), and the capacitor 3
Reference numeral 9 is for stabilizing the instantaneous power supply voltage (for example, 1 μF).

The only active element of this circuit is the transistor 2
2 and its collector drives the intermediate tap of the coil 3 of the output tank circuit 66 consisting of the transmitter coil 3 and the output resonance semi-fixed capacitor 24. The output tank circuit 66 uses the stored electric vibration as its output. The output waveform is a sine wave. The current flowing from the positive terminal of the battery 36, which is the power source, is
The power supply switch 37, mainly the output resonance coil 3, the collector and emitter of the transistor 22, the emitter resistor 23, and the surge current prevention resistor 38, and the battery 3
Return to the negative terminal of 6.

A part of the electric vibration of the output tank circuit 66 causes the ceramic vibrator 20 to electro-mechanically vibrate through the resistor 27. Since the resonance dividing capacitors 28 and 29 are mounted in parallel with the ceramic oscillator 20, they slightly shift the electro-mechanical vibration frequency, but since the midpoints of the capacitors 28 and 29 are connected to the power supply line as shown in the figure. ,
It has a role of making both ends of the ceramic oscillator 20 in opposite phases to the power supply level. The switch 33 is a side switch of the signal pen 4, which is pressed by the operator's finger and is one of the pen statuses. When the switch 33 is pressed, the capacitor 30 is connected in parallel with the ceramic vibrator 20, and the electro-mechanical vibration frequency (for example, 455).
kHz) is lowered by several kHz. The switch 35 is a stylus pressing switch, which is turned on when the operator presses the pen stylus 5 of the signal pen 4 on the tablet board surface.
This is also one of the pen statuses, and the switch 35 turns off.
When N, the capacitor 31 lowers the oscillation frequency by several kHz as in the capacitor 30. The capacitance values of the capacitors 30 and 31 are different, so that four electro-mechanical vibration frequencies are obtained for the four state combinations of the switches 33 and 35. The resistors 32 and 34 are high resistors (for example, 10 MΩ) for fixing the DC level of the frequency shift capacitors 30 and 31, and prevent a sudden change in the DC bias value of the circuit at the moment when the switches 33 and 35 are turned on.

The ceramic oscillator 20 is electro-mechanically oscillated by being driven through the resistor 27, but an opposite-phase AC voltage is induced at its opposite terminal as described above, and the base of the transistor 22 is AC-driven via the resistor 25. To drive. Resistance 2
Reference numeral 6 is a relatively high resistance value (200 kΩ to 3 MΩ) for applying the operation DC bias of the transistor 22.
The resistor 25 is not necessarily required, but is a resistor of, for example, 1 kΩ that has a role of stably operating the transistor 22 and a role of giving voltage compliance to the ceramic vibrator 20. The Schottky barrier diode 21 is connected from the base of the transistor 22 to the collector, and the detailed description of its function will be given later. Although the resistor 23 is inserted between the emitter of the transistor 22 and the negative power supply line, it has a role of stably operating the transistor 22 and a role of operating the transistor 22 close to an ideal current source.
The resistance value is 10 to 100Ω.

Here, the oscillating operation of this circuit will be described in detail. When the power switch 37 is turned on, the capacitor 39 is charged through the resistor 38 and quickly reaches a steady voltage of about 1.55V. Initially, neither the output tank circuit 66 nor the ceramic oscillator 20 electrically vibrates, but the output tank circuit 66 is vibrated and vibrated slightly due to a slight fluctuation of the power supply voltage or a minute noise generated by the transistor 22. A part of the minute vibration is also transmitted to the ceramic vibrator 20 via the resistor 27 to start the electro-mechanical minute vibration. Transistor 22
Is fed back to the base as a slight voltage oscillation of the opposite phase, is phase-inverted and amplified by the transistor 22, and its collector drives the output tank circuit 66 in the same phase. This positive feedback loop, which has a degree of amplification, causes the electric vibration to gradually increase. The operation of the transistor 22 in this initial stage is a class A amplification operation, and if the resonance frequency of the output tank circuit 66 is a frequency near the frequency of the ceramic vibrator, this circuit will always start oscillating.

The oscillation frequency of this circuit depends on the transistor 22.
Is mainly determined by the frequency of the ceramic oscillator 20 that determines the AC voltage to be returned to the base of, and the influence on the oscillation frequency of the output tank circuit 66 will be described later. When the above-mentioned oscillating voltage becomes large, at the negative side peak from the conduction start base voltage level of the transistor 22,
The base voltage becomes low. From this stage, only an intermittent current flows through the transistor, and the collector of the transistor 22 drives the output tank circuit 66 as a kind of switching drive. The output tank circuit 66 maintains the sinusoidal vibration even in the switching drive.

When the oscillating voltage further increases, the base and collector of the transistor 22 have opposite phases,
The positive peak voltage of the base becomes larger than the negative peak voltage of the collector. (See FIG. 3) The role of the Schottky barrier diode 21 is to prevent the transistor 22 itself from being strongly conducted to the saturation conduction region as generally well known, and secondly to the output tank circuit 66. Controlling the vibration level to a constant value. The operation will be described in detail. The collector voltage waveform 41 in FIG. 3 is the base voltage waveform 44.
The current becomes lower than the peak time and the current as shown by the current waveform 47 of the Schottky barrier diode 21 flows intermittently. The current flowing through the DC bias applying resistor 26 is the intermittent current flowing to the base of the transistor 22 and the intermittent current flowing to the Schottky barrier diode 21.
Since it flows to both, the average voltage drop of the resistor 26 becomes large, the base DC bias voltage of the transistor 22 becomes deep, the current driving the output tank circuit 66 of the collector also decreases, and the output oscillating voltage does not increase any more. Since feedback is applied in such an actual operation, even if the switches 33 and 35 are turned on and the oscillation frequency is shifted,
Or fine-tune the output resonance coil (the purpose will be described later)
Even if the hFE of the transistor 22 varies or the coupling coefficient between the transmission coil 3 and the loop electrode wire 7 of the tablet 6 changes, the output is kept substantially constant.

In such a steady state, the base voltage of the transistor 22 becomes a deep DC bias voltage due to the above action as shown by the waveform 44, and the transistor 22 is turned on only near the peak value of the oscillating voltage, and the waveform 46.
The collector current waveform is as shown in (the direction of flowing into the collector is shown as a negative direction). This is because the transistor is operating in class C, and the circuit operation is very efficient with respect to the power consumption current. Conversely, the resistance value of the DC bias applying resistor 26 is selected so that such an operating state is achieved.

As shown in waveforms 40 and 41, the output tank circuit 66 oscillates centering on the positive power supply voltage level and greatly exceeding the positive power supply voltage for a half cycle, so that a large oscillating voltage level can be obtained. . Further, the voltage at the point A (see FIG. 2) is obtained by boosting the collector voltage of the transistor 22.
A large output AC voltage level is reached, and a large output resonance current flows through the output transmission coil 3.

The oscillation frequency is basically determined by the electro-mechanical vibration frequency of the ceramic vibrator 20, but in the case of this circuit, the reactance component of the output tank circuit 66 is changed by the resistor 27 (for example, 22 kΩ) to the ceramic vibrator. Since it is loosely coupled with 20, the semi-fixed resonance capacitor 24
The oscillation frequency can be finely adjusted by adjusting. Therefore, each ceramic oscillator has a frequency error, which can be practically eliminated. Four
In the case of the 55kHz ceramic oscillator, the frequency shift of up to about 5kHz is applied to the four types of pen status, so a frequency error of several hundreds of Hz will be a problem.
This error adjustment function is important.

In FIG. 2, the resonance frequency of the output tank circuit 66 is adjusted by changing the capacitance of the semi-fixed capacitor, but the inductance of the resonance type transmission coil 3 may be changed. In the case of this circuit, the voltage output at point A is 455kHz
With 5.5 Vpp, it is only about 5 from the 1.55 V power supply.
It consumes only 5 μA and has very low power consumption. With one SR48 type silver oxide button battery, a battery life of 2 years could be realized under normal use.

Unlike the Pierce CB oscillator circuit, this circuit stably oscillates regardless of whether the resonance circuit connected to the collector of the transistor is inductive or capacitive. Therefore, whether the frequency error of the ceramic oscillator 20 is positive or negative, the resonance frequency of the output tank circuit 66 can be adjusted without anxiety (adjusting the reactance component of the output tank circuit 66 at the frequency of the ceramic oscillator 20). The oscillation frequency can be corrected. Also, for reference, the unadjusted ceramic oscillator circuit without the output resonance capacitor 24 of this circuit oscillates but its output waveform is about 1V.
It has a pulse shape with a duty ratio of 20% to 30% of pp and is very far from a sine wave. The fundamental wave (sine wave) component of this waveform is 1 Vpp or less, and the current consumption is about 130 μA, which is inefficient, and it is unusable due to the poor waveform for the signal pen of the coordinate detecting device. If the circuit constant in that case is not appropriate, oscillation of a spurious frequency other than the original frequency easily occurs and becomes unstable.

Next, an embodiment of the batteryless signal pen will be described with reference to FIG. The signal generating circuit portion is the same as that of FIG. The power supply method differs from that shown in FIG. 2 only in that the power is supplied from the coordinate detecting device main body to the signal pen without a cable, instead of the battery. An exciting loop coil 56 is arranged around the tablet 6 of the main body of the coordinate detecting device. An AC power current is passed through the excitation loop coil 56 by an AC power oscillator 57 having a frequency different from that of the AC signal generated by the signal pen 4. The capacitor arranged in parallel with the excitation loop coil 56 resonates in parallel with the excitation loop coil 56 and has a role of reducing power loss.

An AC power receive coil 50 is arranged in the signal pen along the pen axis direction, and is wound around a rod-shaped ferrite core. A capacitor 51 is connected to both ends of the AC power receive coil 50 to form a parallel resonance circuit, the resonance frequency of which is the frequency of the AC power oscillator 57. When the signal pen is in use on the board surface of the tablet 6, the AC power receive coil 50 and the excitation loop coil 56 are mutual inductance-coupled as indicated by the symbol M55 in FIG. 4, and a resonance current is generated in the AC power receive coil 50. Induced. A part of this resonance current is taken out from the tap in the middle of the AC power receive coil 50 by the two rectifying diodes 52 and 53, converted into DC, and applied to the voltage stabilizer 54. The voltage stabilizer 54 supplies a DC voltage of, for example, 2.5 V to the aforementioned AC signal generating circuit as a power source. Since the aforementioned AC signal generation circuit has the lowest power consumption ever, the cable-less power supply of FIG. 4 can be realized at a low cost.

Next, an embodiment of a signal pen which is powered by a solar cell will be described with reference to FIG. The signal generating circuit portion is the same as that of FIG. The solar cell 60 is arranged around the upper cylinder of the signal pen to generate electric power by light during use in a bright place. Most of the output of the solar cell 60 is applied to the voltage stabilizer 65 via the diode 62. A part of the output of the solar cell 60 is applied to the secondary battery charge controller 61. The secondary battery charge controller 61 charges the secondary battery 64 only when the secondary battery 64 is not in a fully charged state and the solar battery 60 has a sufficient amount of power generation. Secondary battery 64
Supplies a current to the voltage stabilizer 65 via the diode 63 when the power generation amount of the solar cell 60 is small, for example, when the signal pen is in the shadow of light. The role of the voltage stabilizer 65 is the same as that of FIG.

[0025]

The signal pen circuit according to the present invention satisfies the contradictory requirements of low power consumption and high output at a high level, and a current consumption of about 55 μA can be realized at a power supply voltage of 1.55V. Therefore, the labor and cost for the user to replace the battery can be saved. In addition, even though it was theoretically possible up to now, it has also realized a power supply without a cable, which could not be realized in practice, and a built-in power supply with a normal pen size using a solar cell is also possible. The active element of the signal generating circuit portion is a single transistor, which can be manufactured at low cost. In addition, the weight of the signal pen has been reduced and operability has been improved. In addition, since variations in individual frequencies of the ceramic oscillator can be corrected by adjusting the resonance frequency of the output tank circuit, the reliability of decoding the switch status of the signal pen is improved despite the narrow band, and a simpler circuit Since the output voltage level could be controlled to be almost constant with this signal pen, even if there are four kinds of frequency shifts by the status switch, the above frequency correction, and even if there are variations in hFE of individual transistors, this signal pen It is possible to detect the coordinates with high accuracy in the coordinate detection device using the.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a coordinate detection device using a signal pen of the present invention.

[Fig.2] Circuit diagram of signal pen powered by battery

FIG. 3 Voltage and current waveforms with respect to power supply level

FIG. 4 is a circuit diagram of a signal pen that is supplied with power by mutual inductance coupling.

FIG. 5: Circuit diagram of signal pen powered by solar cell

[Explanation of symbols]

 1 AC signal generator 2 Battery as power supply unit 3 Transmission coil 4 Signal pen 5 Pen stylus 6 Tablet 7 Loop electrode wire 8 X-direction analog multiplexer 9 Y-direction analog multiplexer 10 Resonance transformer 11 Amplifier 12 Signal level detection unit 13 Control unit 20 Ceramic resonator 21 Schottky barrier diode 22 Transistor 23 Emitter resistance 24 Output resonance semi-fixed capacitor 25 Base resistance 26 DC bias applying resistance 27 Ceramic resonator drive resistance 28 Resonance division capacitor 29 Resonance division capacitor 30 Frequency shift capacitor 31 Frequency shift capacitor 32 DC level fixed resistance of the capacitor 30 33 Side switch 34 DC level fixed resistance of the capacitor 31 35 Stylus pressing switch 36 Battery 37 Power switch 38 Surge current prevention resistor 39 Instantaneous power supply voltage stabilizing capacitor 40 Point A voltage waveform 41 Transistor collector voltage waveform 42 Positive power supply voltage level 43 Transistor start base voltage level 44 Transistor base voltage waveform 45 Negative power supply voltage Level 46 Transistor collector current waveform 47 Schottky barrier diode current waveform 50 AC power receive coil 51 AC power resonance capacitor 52 Rectifier diode 53 Rectifier diode 54 Voltage stabilizer 55 Mutual inductance coupling 56 Excitation loop coil 57 AC power oscillator 60 Solar cell 61 Secondary Battery Charge Controller 62 Diode 63 Diode 64 Secondary Battery 65 Voltage Stabilizer 66 Tank Circuit

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[Procedure amendment]

[Submission date] March 9, 1995

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Claims (4)

[Claims] 1. A signal-indicating signal pen circuit without a cable that abuts a tablet having a grid-shaped loop electrode wire in a mutual inductance coupling type coordinate detecting device, wherein the signal is a mutual inductance-coupled signal with the loop electrode wire of the tablet. An output tank circuit that can adjust the resonance frequency consisting of a resonance type transmission coil and a resonance capacitor at the tip of the pen,
A transistor of class C operation whose collector current drives a tap in the middle of the transmission coil, a Schottky barrier diode connected from the base of the transistor toward the collector, and a drive resistor on the collector side between the collector and the base of the transistor. A signal pen circuit, comprising: a ceramic oscillator connected through an unadjusted oscillation via a ceramic oscillator; and an oscillation frequency shifting capacitor that can be connected to and separated from the ceramic oscillator in parallel. 2. The signal pen circuit according to claim 1, wherein power is supplied from a battery. 3. The signal pen circuit according to claim 1, wherein electric power generated inductively without a cable is converted into a direct current, the voltage is stabilized, and power is supplied by mutual inductance coupling. 4. The signal pen circuit according to claim 1, wherein the voltage generated by the solar cell is stabilized and power is supplied.