JP3412240B2 - Signal pen circuit - Google Patents

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 comes into contact with a tablet of a capacitive coupling type coordinate detecting device.

[0002]

2. Description of the Related Art As a circuit used in a conventional coordinate-pointing signal pen without a cable, a CMOS inverter oscillates and the signal boosts the power supply voltage of the final-stage CMOS inverter, which is higher than the battery voltage. A circuit that outputs an AC pulse signal of a voltage is known. There is also known a technique of applying a rectangular wave signal created by an ordinary digital logic to an output series LC resonance circuit, but not as a signal pen circuit, to obtain a sine wave output voltage 1.5 times or more larger than a power supply voltage. There is. Further, as a general oscillator using a crystal oscillator or a ceramic oscillator, a Pierce BE circuit, a Pierce CB circuit, and an unadjusted type circuit are well known, and the output voltage thereof is a high frequency transformer. It is easy to imagine that the voltage can be boosted.

[0003]

The conventional signal pen uses four or more batteries to obtain a high voltage output. In addition, since the power supply current is large and 300 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. In addition, the number of active circuit elements is large (three or more inverter amplifiers are used) and the cost is high.

[0004]

Means for Solving the Problems The present invention has been made in view of the above-mentioned conventional problems, and is in contact with a tablet having a grid-shaped electrode wire of a capacitive coupling type coordinate detection device for transmitting a pseudo-balanced signal. An output tank circuit which is a signal pen circuit for coordinate indication without a cable and which is composed of a coil and a capacitor connected to two conductors at the tip of the signal pen for capacitively coupling with the electrode wire of the tablet and which can adjust the resonance frequency, A transistor of class C operation whose collector current drives a midway tap of the 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. And a ceramic oscillator that is connected to an unadjusted oscillator and an oscillator that can be connected to and separated from the ceramic oscillator in parallel. A signal pen circuit composed of a wave number shifting capacitor 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. The voltage between both ends of the output tank circuit becomes higher than that of the tap on the way and is boosted here. In addition, since the Schottky barrier diode is mounted from the base of the transistor to the collector, the base drive DC level is automatically adjusted, and even if there is a variation in hFE of the transistor, or the ceramic oscillator is shifted by a minute frequency. Moreover, even if the resonance frequency of the output tank circuit deviates to some extent, the output voltage is kept substantially constant. Further, 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 capacitive coupling type coordinate detecting device using the present signal pen. A pseudo-balanced AC signal generator 1 of an active circuit is arranged inside the signal pen 5, generates a continuous AC signal, and applies the balance to the stylus conductor 3 and the ring-shaped conductor 4 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 stylus conductor 3 and the ring-shaped conductor 4 at the tip of the signal pen 5 are near the board surface of the tablet 6,
.. of the tablet 6 is capacitively coupled with a small capacitance. Therefore, the balanced electric signal between the stylus conductor 3 and the ring-shaped conductor 4 at the tip of the signal pen 5 is transmitted to the adjacent electrode lines 7, 7, ... Of the tablet 6 in a pseudo-balanced manner at a level according to the magnitude of the coupling capacitance. To be done.
The X-direction and Y-direction analog multiplexers 8 and 9 sequentially switch the adjacent two-electrode lines of the respective electrode lines 7, 7, 7, ... while forming a pair so that the pseudo-balanced AC signals received by the respective two-electrode lines are AC-coupled. It is applied to the balanced type current buffer amplifier 18 via the ring capacitors 16 and 17. The X direction and the Y direction operate in a time division manner. For example, when the X direction analog multiplexer 8 selects any adjacent electrode lines 7, 7, the Y direction analog multiplexer 9
Is off.

The balanced output of the current buffer amplifier 18 is applied to a balanced / unbalanced converter 19 with a bandpass filter, passes only a required frequency band, and is converted into an unbalanced voltage signal.
This unbalanced voltage signal is amplified by the amplifier 20 to a voltage level sufficient for measurement, and the frequency is measured by the controller 22 and the voltage level is measured by the signal level detector 21.

Regarding this voltage level measurement and coordinate determination,
It will be described here as it relates to the required characteristics of the signal pen. An AC signal between two adjacent electrode lines of the electrode lines 7, 7, 7, ... On the tablet 6 is balanced by a current buffer amplifier 18
In order to observe through the balance-unbalance converter 19 with a bandpass filter, the position of the stylus conductor 3 at the tip of the signal pen 5 on the tablet 6 on the X axis (the same applies to the Y axis position), Although the signal detection level is shown in FIG. 2, it has a bilaterally symmetrical characteristic with a dip in the center. A characteristic curve 23 is a signal detection level characteristic by the n and n + 1th electrode lines 7 and 7 where n is an arbitrary electrode line, and a characteristic curve 24 is a characteristic by the n + 1 and n + 2nd electrode lines 7 and 7. Curve 25 is the n + 2 and n + 3th electrode wire 7,
7 is the characteristic. Signal pen 5 is at a specific position (P position)
In the case of 1), it is detected as A level, B level, and C level, respectively, as shown in the figure, and the P position is interpolated from these detected levels by calculation or table to determine the coordinates.
Therefore, the output level of the signal pen needs to be stably maintained at a constant level, and if the level fluctuates, accurate coordinate determination cannot be performed. Further, the larger the output voltage of the signal pen is, the better in order that the overall amplification on the receiving side is very large and the signal processing is performed with a good S / N ratio.

A signal pen circuit that meets the above-mentioned conditions will be described below. FIG. 3 shows the entire circuit of the signal pen 5 powered by one silver oxide button battery. A battery 47 of about 1.55V supplies the operating power of this circuit. The resistor 49 is for preventing surge current (for example, 100Ω), and the capacitor 5
0 is for stabilizing the instantaneous power supply voltage (for example, 1 μF).

The only active element of this circuit is the transistor 3
2 and its collector is the output tank circuits 34 and 35.
The intermediate tap of the coil 34 is driven. The output tank circuits 34 and 35 use the stored electric vibration as the output of the parallel resonance circuit to drive the stylus conductor 3 and the ring-shaped conductor 4 at the tip of the signal pen 5 in a pseudo equilibrium voltage as shown in FIG. The output waveform is a sine wave. The current flowing from the positive terminal of the battery 47, which is a power source, passes through the power switch 48, mainly through the output resonance coil 34, through the collector and emitter of the transistor 32, through the emitter resistor 33 and the surge current prevention resistor 49, and the battery 47. Return to the negative terminal of.

A part of the electric vibration of the output tank circuits 34 and 35 electrically connects the ceramic vibrator 30 to the electric resistance via the resistor 38.
Make the machine vibrate. Since the resonance dividing capacitors 39 and 40 are mounted in parallel with the ceramic oscillator 30, they slightly shift the electro-mechanical vibration frequency, but the midpoints of the capacitors 39 and 40 are connected to the power supply line as shown in the figure. , And has the role of making both ends of the ceramic vibrator 30 have opposite phases to the power supply level. The switch 44 is a side switch of the signal pen 5, is pressed by the operator's finger, and is one of the pen statuses. When the switch 44 is pressed, the capacitor 41 is connected in parallel with the ceramic vibrator 30, and the electro-mechanical vibration frequency (for example, 455 kHz) is lowered by several kHz. Also switch 4
A stylus pressing switch 6 is turned on when the operator presses the stylus 3 of the signal pen 5 on the tablet board surface. This is also one of the pen statuses, and the switch 46
When is turned on, the capacitor 42 also lowers the oscillation frequency by several kHz. The capacitance values of the capacitors 41 and 42 are different, and four electro-mechanical vibration frequencies are obtained for the four state combinations of the switches 44 and 46.
The resistors 43 and 45 are high resistances (for example, 10 MΩ) for fixing the DC level of the frequency shift capacitors 41 and 42.
This prevents a sudden change in the DC bias value of the circuit at the moment when the switches 44 and 46 are turned on.

The ceramic oscillator 30 is electro-mechanically oscillated by being driven through the resistor 38, but an opposite-phase AC voltage is induced at its opposite terminal as described above, and the base of the transistor 32 is AC-coupled through the resistor 36. To drive. Resistance 3
Reference numeral 7 is a relatively high resistance value (200 kΩ to 3 MΩ) for applying the operation DC bias of the transistor 32.
The resistor 36 is not necessarily required, but is a resistor of, for example, 1 kΩ that has a role of stably operating the transistor 32 and a role of giving voltage compliance to the ceramic vibrator 30. The Schottky barrier diode 31 is connected from the base of the transistor 32 to the collector, and the detailed description of its function will be given later. Although the resistor 33 is inserted between the emitter of the transistor 32 and the negative power supply line, it has a role of stably operating the transistor 32 and a role of making the transistor 32 operate 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 48 is turned on, the capacitor 50 is charged through the resistor 49 and quickly reaches a steady voltage of about 1.55V. Initially the output tank circuits 34 and 3
Neither 5 nor the ceramic oscillator 30 is electrically vibrated, but the output tank circuits 34 and 35 are vibrated and vibrated slightly due to a slight fluctuation of the power supply voltage or a minute noise generated by the transistor 32. A part of the minute vibration is also transmitted to the ceramic vibrator 30 via the resistor 38 and starts the electro-mechanical minute vibration.
It is fed back to the base of the transistor 32 as a slight voltage oscillation of the opposite phase, phase inverted and amplified by the transistor 32, and its collector drives the output tank circuits 34 and 35 in the same phase. This positive feedback loop, which has a degree of amplification, causes the electric vibration to gradually increase. Transistor 3 at this early stage
The operation of No. 2 is a class A amplification operation, and if the resonance frequency of the output tank circuits 34 and 35 is a frequency near the frequency of the ceramic vibrator, this circuit always starts oscillation.

The oscillation frequency of this circuit is the transistor 32.
The output tank circuit 3 is determined mainly by the frequency of the ceramic oscillator that determines the AC voltage that returns to the base of the
The influence of 4 and 35 on the oscillation frequency will be described later.
When the above-mentioned oscillating voltage increases, the transistor 32
The base voltage becomes lower at the negative side peak than the conduction start base voltage level. From this stage, only an intermittent current flows in the transistor, and the collector of the transistor 32 drives the output tank circuits 34 and 35 as a kind of switching drive. Even with switching drive, the output tank circuits 34 and 35 maintain sinusoidal vibration.

As the oscillating voltage further increases, referring to FIG. 4, since the base and collector of the transistor 32 are in opposite phase, the positive peak voltage of the base becomes larger than the negative peak voltage of the collector. The role of the Schottky barrier diode 31 is to prevent the transistor 32 itself from conducting strongly to the saturation conduction region as generally well known, and secondly to the output tank circuits 34 and 3.
5 is to control the vibration level of 5 to a constant value. The operation will be described in detail. The collector voltage waveform 52 in FIG. 4 becomes lower than the base voltage waveform 55 at the peak time point, and the current as shown by the current waveform 58 of the Schottky barrier diode 31 flows intermittently. DC bias applying resistor 37
Current flows through both the intermittent current flowing to the base of the transistor 32 and the intermittent current flowing to the Schottky barrier diode 31, so that the average voltage drop of the resistor 37 increases and the base DC bias voltage of the transistor 32 increases. , Collector output tank circuits 34 and 35
The current for driving is also reduced, and the output oscillating voltage does not increase any further. Since feedback is applied during actual operation, even if the switches 44 and 46 are turned on and the oscillation frequency is shifted, or the output resonance coil is finely adjusted (the purpose will be described later), or the transistor 32 is turned on. h
Even if the FE varies, the output voltage is kept almost constant.

In such a steady state, the base voltage of the transistor 32 becomes a deep DC bias voltage due to the above action as shown by the waveform 55, and the transistor 32 is made conductive only near the peak value of the oscillating voltage, and the waveform 57 is obtained.
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 37 is selected so that such an operating state is achieved.

As shown by the waveforms 51 and 52, the output tank circuit oscillates centering on the positive power supply voltage level and greatly exceeding the positive power supply voltage for a half cycle, so a large oscillating voltage level can be taken. Further, the output voltage becomes a large output AC voltage level by boosting the collector voltage of the transistor 32. The output impedance is large, but the stylus conductor 3 at the tip of the signal pen and the electrode wire 7 of the tablet 6
Since the coupling capacitance between them is 1 pF or less in a normal use state, the signal leakage to the load is a level that can be practically ignored. Further, since the stray capacitance between the stylus conductor 3 and the ring-shaped conductor 4 at the tip of the signal pen is considered to be included in the output resonance capacitor 35, the output tank circuits 34 and 35 are hardly burdened. Therefore, as shown in FIG. 3, the output tank circuit 3
There is no problem in directly outputting the high voltage levels across 4 and 35.

The oscillation frequency is basically determined by the electro-mechanical vibration frequency of the ceramic oscillator 30, but in the case of this circuit, the reactance components of the output tank circuits 34 and 35 are made ceramic by a resistor 38 (for example, 22 kΩ). Since it is loosely coupled to the oscillator 30, by adjusting the output resonance coil 34, which is a semi-fixed inductance,
The oscillation frequency can be finely adjusted. Therefore, each ceramic oscillator has a frequency error, which can be practically eliminated. In the case of a 455-kHz ceramic oscillator, since a maximum frequency shift of about 5 kHz is performed with respect to four types of pen statuses, a frequency error of several hundreds Hz becomes a problem, so this error adjustment function is important.

The output resonance coil 34 is housed in a shield case to avoid unnecessary electromagnetic coupling with the circuit pattern. In FIG. 3, the resonance frequencies of the output tank circuits 34 and 35 are adjusted by changing the inductance of the coil, but the capacitance of the resonance capacitor 35 may be changed.
In the case of this circuit, when the output is set to 455 kHz and 5.5 Vpp, about 85 μA current is simply consumed from the 1.55 V power source, which is extremely low power consumption. One SR48 type silver oxide button battery could realize a battery life of one year 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, regardless of whether the frequency error of the ceramic oscillator 30 is positive or negative, the resonance frequency of the output tank circuits 34 and 35 can be adjusted without anxiety (the reactance components of the output tank circuits 34 and 35 at the frequency of the ceramic oscillator 30 can be adjusted). You can adjust the oscillation frequency. Also, for reference, in the case of the unadjusted ceramic oscillator circuit in which the output tank circuits 34 and 35 of this circuit are replaced by resistors, the output waveform is about 1 Vpp of 20% to 3%.
It is a pulse with a 0% duty ratio and has a blunt rising and falling waveform, which is very different from a sine wave. The fundamental wave (sine wave) component of this waveform is 1 Vpp or less, and its current consumption is about 90 μA, which is inefficient. Further, if the output voltage is boosted five times or more by a high frequency transformer, it will be affected by transformer loss and stray capacitance. The current consumption is more than twice this, and it is not usable for signal pen of the coordinate detecting device due to the bad waveform. 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. Since the signal generating circuit portion is exactly the same as that of FIG. 3, its explanation is omitted. The power supply method differs from that of FIG. 3 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 66 is arranged around the tablet 6 of the main body of the coordinate detecting device. An AC power current is supplied to the excitation loop coil 66 by an AC power oscillator 67 having a frequency different from that of the AC signal generated by the signal pen. The capacitor arranged in parallel with the excitation loop coil 66 resonates in parallel with the excitation loop coil 66 and serves to reduce power loss.

An AC power receive coil 60 is arranged in the signal pen along the pen axis direction, and is wound around a rod-shaped ferrite core. A capacitor 61 is connected to both ends of the AC power receive coil 60 to form a parallel resonance circuit, the resonance frequency of which is the frequency of the AC power oscillator 67. When this signal pen is in use on the board surface of the tablet 6, the AC power receive coil 60 and the excitation loop coil 66 perform mutual inductance coupling indicated by the symbol M65 in FIG. 5, and a resonance current is generated in the AC power receive coil 60. Induced. A part of this resonance current is taken out from the tap in the middle of the AC power receive coil 60 by the two rectifying diodes 62 and 63, converted into DC, and applied to the voltage stabilizer 64. The voltage stabilizer 64 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. 5 can be realized at a low cost.

Next, an embodiment of a signal pen that is powered by a solar cell will be described with reference to FIG. Since the signal generating circuit portion is exactly the same as that of FIG. 3, its explanation is omitted. The solar cell 70 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 70 is applied to the voltage stabilizer 75 via the diode 72. A part of the output of the solar cell 70 is applied to the secondary battery charge controller 71. The secondary battery charge controller 71 charges the secondary battery 74 only when the secondary battery 74 is not in a fully charged state and the solar battery 70 has a sufficient amount of power generation. Secondary battery 74
Supplies current to the voltage stabilizer 75 via the diode 73 when the amount of power generated by the solar cell 70 is small, for example, when the signal pen is in the shadow of light. The role of the voltage stabilizer 75 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 voltage at a high level, and can be realized with a current consumption of about 85 μA 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, variations in the individual frequencies of the ceramic oscillator can be corrected by adjusting the resonance frequency of the output tank circuit.
The decoding reliability of the switch status of the signal pen was improved despite the narrow band, and the output voltage level could be controlled to be almost constant with a simpler circuit. Even if the above frequency correction is performed, even if there is a variation in hFE of each transistor, the coordinate detection device using this signal pen can accurately detect coordinates.

[Brief description of drawings]

FIG. 1 is a block diagram of a coordinate detection device using this signal pen.

FIG. 2 is a signal detection level characteristic diagram of a coordinate detection device using this signal pen.

FIG. 3 is a circuit diagram of a signal pen powered by a battery.

FIG. 4 Voltage and current waveforms with respect to power supply level

FIG. 5 is a signal pen circuit diagram in which power is supplied by mutual inductance coupling.

FIG. 6 is a circuit diagram of a signal pen powered by a solar cell.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 AC signal generator 2 Power supply section 3 Stylus conductor at tip of signal pen 4 Ring conductor 5 at tip of signal pen 5 Signal pen 6 Tablet 7 Electrode wire 8 X direction analog multiplexer 9 Y direction analog multiplexer 10 DC level fixing resistor 11 Resistor for fixing DC level 12 Resistor for fixing DC level 13 Resistor for fixing DC level 14 DC current sink resistor 15 DC current sink resistor 16 AC coupling capacitor 17 AC coupling capacitor 18 Balanced current buffer amplifier 19 Unbalanced with bandpass filter Balance converter 20 Amplifier 21 Signal level detection unit 22 Control unit 23 Signal level detection characteristic by n and n + 1th electrode line 24 Signal level detection characteristic by n + 1 and n + 2nd electrode line 25 Signal level by n + 2 and n + 3rd electrode line Detection characteristics 30 sec Mic oscillator 31 Schottky barrier diode 32 Transistor 33 Emitter resistor 34 Output resonant coil 35 Output resonant capacitor 36 Base resistor 37 DC bias applying resistor 38 Ceramic oscillator drive resistor 39 Resonant split capacitor 40 Resonant split capacitor 41 Frequency shift capacitor 42 Frequency shift Capacitor 43 DC level fixed resistor 44 of capacitor 41 Side switch 45 DC level fixed resistor of capacitor 42 Stylus pressing switch 47 Battery 48 Power switch 49 Surge current prevention resistor 50 Instantaneous power supply voltage stabilizing capacitor 51 Output voltage waveform 52 Transistor collector voltage Waveform 53 Positive power supply voltage level 54 Transistor start conduction base voltage level 55 Transistor base voltage waveform 56 Negative power supply voltage level 7 Transistor collector current waveform 58 Schottky barrier diode current waveform 60 AC power receive coil 61 AC power resonance capacitor 62 rectifier diode 63 rectifier diode 64 voltage stabilizer 65 mutual inductance coupling 66 excitation loop coil 67 AC power oscillator 70 Solar cell 71 Secondary battery charge controller 72 Diode 73 Diode 74 Secondary battery 75 Voltage stabilizer

Claims (4)

(57) [Claims] 1. A signal-pointing pen circuit for coordinate indication, which is in contact with a tablet having a grid-like electrode wire, of a capacitive detection type coordinate detecting apparatus for transmitting a pseudo-balanced signal, and which does not have a cable,
An output tank circuit including a coil and a capacitor connected to two conductors at the tip of the signal pen that capacitively couples with the electrode wire of the tablet, and an output tank circuit capable of adjusting the resonance frequency, and a collector current driving a tap in the middle of the coil. Class operation transistor, a Schottky barrier diode connected from the base of the transistor to the collector, and a ceramic resonator connected between the collector and the base of the transistor through a drive resistor on the collector side without adjustment to oscillate. A signal pen circuit comprising: 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.