JP3860848B2 - High voltage stylus for portable computers - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a stylus for use with a digital pad. This type of pad takes the form of a transparent overlay on the digital display of a portable computer.
[0002]
[Background Art and Problems to be Solved by the Invention]
FIG. 1 is a highly simplified view of a digital pad and its associated stylus 6. When active, the stylus 6 generates a signal 9 as shown in FIG. This signal induces currents I1 through I4, which are detected by a current-to-voltage amplifier.
[0003]
Each current-to-voltage amplifier generates a voltage representing the magnitude of the current. A processing circuit known in the prior art receives the voltage signal and further calculates the position of the stylus signal 6 based on this voltage signal.
[0004]
The currents I1 to I4 are induced because the stylus 6 operates like one plate of capacitors. A digital pad (producing a resistive surface that is a material such as indium tin oxide) behaves like any other plate. As shown in FIG. 3, when a negative charge is applied to the tip 2 of the stylus 6, the positive charge is induced on the surface of the pad 6. This positive charge is applied by the currents I1 to I4. Conversely, as shown in FIG. 4, the positive charge at the tip 2 of the stylus 6 induces a positive charge on the pad. Negative charges are applied by the currents I1 to I4.
[0005]
The relative magnitude of the current depends on the position of the stylus. If the stylus is in the position shown in FIG. 5, the current I1 is the largest, the current I4 is the next largest, and the currents I2 and I3 are substantially the same.
[0006]
If the stylus is in the position shown in FIG. 6, the current I4 is the highest, the current I1 is the next highest, and so on. The difference in current magnitude is the difference in voltage produced by the current versus voltage amplifier of FIG.
[0007]
In addition to the signal produced by the stylus, the noise current vs. voltage amplifier generates other unwanted signals. For example, near a cathode ray tube, fluorescence and electric motors induce charge on the digital pad. Furthermore, “static electricity” is applied to the pad when touched by the user, especially when the ambient air is dry.
[0008]
Because there is an undesired signal called “noise”, it is desirable to use a stylus that generates as large a signal as possible from the noise signal. That is, the signal to noise ratio needs to be maximized. If there is no limit on size and power consumption, there is no problem in obtaining a large signal-to-noise ratio. However, the stylus is designed for portability. In order to operate with a battery, it is necessary to reduce power consumption and extend the battery life.
[0009]
Obtaining a large signal-to-noise ratio from a stylus is not a minor problem.
[0010]
An object of the present invention is to present an improved stylus for a digital pad.
[0011]
Another object of the present invention is to provide an improved stylus for a portable digital pad that generates a large position signal.
[0012]
[Means for Solving the Problems]
To achieve the above object, the present invention provides a high voltage stylus for a digital pad, comprising: (a) a transformer having a pair of primary windings; and (b) two different sine waves having a phase difference. And a means for supplying a signal to the primary winding of the transformer. The present invention also includes (a) means for generating a sine wave signal, (b) first amplification means for amplifying the sine wave signal, and (c) inverter means for inverting the sine wave signal; (D) second amplification means for amplifying the inverted signal of the sine wave signal; and (e) a set of primary conductors and a set of secondary conductors, and one of the primary conductors A transformer connected to the output of the first amplifying means and the output of the second amplifying means connected to the other; and (f) a tip connected to the output of the secondary conductor. A high voltage stylus device characterized by the above is provided.
[0013]
【Example】
The present invention can be explained by first illustrating a simple but not optimal method for generating large stylus signals. This method uses a voltage transformer 14 as shown in FIG. (The voltages described here are somewhat arbitrary and have been chosen for ease of explanation. The actual voltages and currents used in the present invention are described in the section “General Considerations” in the title.)
The sine wave 12 is amplified by an amplifier A having a gain of K. The output signal of the amplifier takes 5.0 volt peak-to-peak as shown. This output signal is applied to the primary side 13 of the transformer 14 having a turns ratio of two. The voltage generated on the secondary side of the transformer is 10 volts peak-to-peak as shown.
[0014]
The present invention has the same turns ratio as in FIG. 7, but uses a transformer of the method shown in FIG. Two amplifiers A1 and A2 are added to the primary winding 15 of the transformer 18. The first amplifier A 1 receives the sine wave 19 directly from the sine wave generator 21. This second amplifier A2 is applied by a sine wave generator, but receives a sine wave inverted by an inverter I (ie, equal but phase shifted by 180 °).
[0015]
The output of each amplifier is a sine wave and is 5.0 volt peak to peak as shown. The voltage appearing on the secondary side of the transformer is about 20 volts peak-to-peak as shown. This voltage is twice that produced by the system of FIG. Obtaining twice the output voltage can be explained with reference to FIG.
[0016]
Consider half the sinusoidal cycle. This half cycle, represented by H1 and generated by the amplifier A1 in FIG. 8, is applied to the primary conductor L1. Inverted, represented as H2, and another half cycle generated by amplifier A2 of FIG. 8 is applied to lead L2.
[0017]
The combined signal applied to the leads L1 and L2 is the difference D1 between H1 and H2. In the difference signal D1, the dotted arrow is taken from H2 and represents the contribution of H2 to the net voltage; the solid arrow is taken from H1 and represents the contribution of H1 to the net voltage.
[0018]
The voltage swing of D1 from zero to positive peak is 5 volts as shown by the swing from point P1 to P2. This runout of 5 volts is twice the runout indicated by the runout from point P3 to point P4 in the case of FIG.
[0019]
The combined voltage of the two additive half cycles is shown in FIG. 10 and is further accurately analyzed in the same manner as the single half cycle of FIG. The voltage applied to the primary side of the transformer of FIG. 10 swings from zero to positive 5.0 volts (ie, from P1 to P2) and from zero to negative 5.0 volts (ie, from P5 to P6).
[0020]
Conversely, the runout in FIG. 7 is zero to positive 2.5 volts (ie, P3 to P4) and zero to 2.5 volts (ie, P7 to P8), that is, half of the runout of FIG.
[0021]
The output of the transformer of FIG. 8 is applied to the tip 2 of the stylus as shown in FIG. The stylus tip 2 represents a capacitive load of about 25 picofarads. However, most of the 25 picofarad capacitance is parasitic capacitance within the pen. The actual capacitance represented by the tip 2 / pad 3 combination is in the range of 1 picofarad.
[0022]
As shown in FIG. 1, the actual transformer 18 has a turns ratio of 10. The sine wave outputs of amplifiers A1 and A2 swing from zero to a power supply voltage that is in the range of about 3.0 to 5.0 volts depending on the device configuration. Assuming that the power supply voltage is 3.0 volts, the zero-positive peak swing applied to the primary is 3.0 volts (ie, the difference between the half cycles of H5 and H6). The transformer output is 30 volts for zero-to-peak, ie, 60 volts for peak-to-peak.
[0023]
This high voltage (60 volts in the case of FIG. 12) can be considered to be obtained by using the apparatus of FIG. 7 and doubling the transformer turns ratio. However, it is not feasible to double this.
[0024]
The aforementioned parasitic capacitance is actually required for the transformer when a capacitive load is used. Due to the capacitive load, doubling the turns ratio causes the current generated on the primary side of the transformer to be too high; ie, quadrupled instead of double. The fourfold increase occurs because the equivalent impedance Zeq that the capacitive load occurs on the primary side of the transformer is equal to 1 / [j × 2 × PI × f × C × (T Squared)]]
Here, j is an imaginary number, f is a hertz frequency, C is a parasitic capacitance value, and T is a turns ratio. FIG. 13 shows this state.
[0025]
It is illustrated that the current is quadruple by two examples, one corresponding to twice the turns ratio and the other corresponding to the turns ratio of the present invention.
[0026]
Example 1: A large number of turns As a simple example, the parameters are as follows:
C = 25 pF;
Frequency = 250 kHz, so that ω is equal to 2 × PI × 250 kHz, ie 1570000 radians / second;
T = 10
The equivalent impedance of the capacitive load appearing in the primary winding (ignoring the impedance of the transformer) Zeq is as follows.
[0027]
Zeq = 1 / [2 * PI * 250 kHz * 25 pF * (10 squared)] = 250 ohm If the voltage V applied to the primary side is 2.5 volts at peak to peak, the resulting current is 2.5 / 250, i.e. 10 mA. This value indicates the current generated when the turns ratio is double.
[0028]
Example 2: When the turn ratio is small as in the present invention, when the turn ratio is reduced to 5, the calculation is exactly the same as in Example 1, and “T item” is 10 squared, ie, 5 instead of 100 Is expected to be squared, or 25. That is,
Zeq = 1 / [2 × PI × 250 kHz × 25 pF × (square of 5)] =
For a V of 2.5 volt peak-to-peak signal applied to the 1000 ohm primary, the resulting current is V / Zeq, or 2.5 / 1000, which is 2.5 mA. The current is ¼ when the turns ratio is twice, but this becomes ¼ of the value when the equivalent impedance is reduced by doubling the turns (ie, 1000 Ω). From 250 to 250 ohms).
[0029]
Therefore, when driving a capacitive load, the current generated on the primary side of the transformer increases by a factor of 4 by doubling the transformer turns ratio and obtaining a high output voltage.
[0030]
This 4-fold increase in current is undesirable. The present invention avoids this increase by avoiding the need to double the turns ratio.
[0031]
There are further reasons to avoid doubling the transformer turns ratio. To double the turns ratio requires (a) reducing the primary turns or (b) increasing the secondary turns (or a combination of both).
[0032]
Reducing the primary volume is not feasible for the following reasons. The primary winding of the transformer is considered an inductor without series resistance. In the preferred embodiment of the application, the value of this inductor is 0.001 Henry. At a good frequency of 125 kHz for the application, the impedance of the inductor is j × (inductance value) × (radian frequency), ie j × (0.001) × (123E3 × 2 × PI), j785 Equal to 5 ohms.
[0033]
The magnitude of this impedance is 785.5 ohms (imaginary number).
[0034]
When the primary turns are halved, the inductance is (almost) divided by a factor of 4,
j785.5 / 4, i.e., j196 ohms (the reason is that the inductance is approximately proportional to the square of the number of turns). The new size is 196 ohms (imaginary number).
[0035]
This new size is 25 percent of the old size; the size is reduced by 75 percent.
[0036]
The decrease in impedance increases the current generated by the primary winding. This increase in current increases the power consumed by the amplifier driving the primary winding. Preferably, the current does not increase or the power consumption does not increase.
[0037]
Although it is feasible as another method to double the number of turns of the secondary winding, it is not performed. Doubling the secondary winding increases the amount of wire required, which is against the goal of reducing the stylus size.
[0038]
In addition, doubling the number of turns increases the secondary winding capacity because adjacent wires separated by an insulator act like a capacitor. This increase in capacity works to increase the capacitive load shown in FIG. Increasing this capacity is not preferred, because the increase causes the transformer primary winding to produce more current as in the previous example.
[0039]
The device contained within the dotted line in FIG. 11 is in the form of a single integrated circuit (IC). (In an actual IC, (a) monitoring the power supply, (b) managing the power of the IC, and (c) controlling the stylus battery status and stylus switch status on the computer or digital pad by telemetry. It includes additional circuitry that performs additional functions such as communicating). The important operating characteristics of the IC are as follows.
[0040]
In one embodiment, the IC is powered from a commercially available battery with each voltage at 1.25 volts and an overall voltage of 3.75 volts. The IC generates approximately 3 milliamperes of current below 4 milliamperes from the battery (this current is applied to both the device shown in FIG. 11 and the additional circuitry). Thus, power consumption is 0.004 amps x 3.75 volts or less, ie 15 milliwatts or less.
[0041]
The IC includes amplifiers A1 and A2, which generate a sine wave signal whose peak-to-peak swings from zero to the supply voltage (3.75 volts in this example). However, the combined voltage applied to the primary side is twice that of the individual sine wave: 2 × 3.75 or 7.5 volts. Again, the voltage swing applied to the primary side is twice the supply voltage.
[0042]
As is well known, commercial manufacturers can make the device shown in FIG. 11 and produce ICs that operate as described.
[0043]
FIG. 12 shows (a) the turn ratio is 10, (b) the primary side voltage is 12 volts at peak-to-peak, and (c) the output voltage is 120 at peak-to-peak. Indicates that it is a bolt.
[0044]
In other embodiments, various output voltages are created by combining the following adjustments:
(1) Changing the power supply voltage by changing the type or number of batteries. This changes the rail-to-rail swing of the amplifiers A1, A2, and thus changes the peak-to-peak voltage applied to the primary side of the transformer.
(2) Changing the turns ratio of the transformer,
(3) changing the gain of the amplifier;
Output voltages on the secondary side of the transformer are obtained, such as 20, 30, 40, 50, 60 and 70 volts or more. High output voltage improves the overall signal-to-noise characteristics of the system.
[0045]
The power supply takes the form of three commercially available batteries that total voltages from 3.1 volts to 4.2 volts. The average of this range of voltages is 3.6 volts and is referred to as “nominal 3.6 volts”.
[0046]
Digital pads that work with the electrostatic pens described herein are commercially available. A manufacturer of this type of pad is the Scriptel company of Columbus, Ohio.
[0047]
The sine wave 21 in FIG. 8 and the opposite wave 23 are 180 degrees out of phase. When the phase angle is 180 degrees, the voltage applied to the primary side is maximum, but it is not strictly necessary that the phase difference is 180 degrees.
[0048]
The sine wave 21 and the opposite wave 23 do not have to have the same amplitude.
[0049]
【The invention's effect】
An important feature of the present invention is to generate a sine wave with zero-to-peak swing equal to the power supply voltage. That is, the gain of the amplifier A1 in FIG. 8 is selected so that the positive fluctuation from the points P1 to P2 in FIG. 9 is equal to the power supply voltage. Similarly, the negative swing shown by half cycle H2 is equal to the power supply voltage (but the polarity is opposite).
[0050]
Combining these two half cycles results in a total primary voltage swing, which is twice the supply voltage when measuring peak-to-peak.
[0051]
It is possible to use a small voltage swing applied to the primary side such that the peak-to-peak swing is 110 percent of the supply voltage.
[0052]
The term “amplitude” indicates zero-to-peak voltage, ie, P1 to P2 in FIG. The peak-to-peak voltage is of course twice the amplitude.
[Brief description of the drawings]
FIG. 1 is a simple representation of a prior art digital pad.
FIG. 2 is a simple representation of a prior art digital pad.
FIG. 3 illustrates how an electrostatic stylus 6 induces charge on a digital pad.
FIG. 4 illustrates how an electrostatic stylus 6 induces charge on a digital pad.
FIG. 5 shows how the currents I1 to I4 change depending on the position of the stylus 6;
FIG. 6 shows how the currents I1 to I4 change depending on the position of the stylus 6;
FIG. 7 illustrates one method for generating a high voltage signal.
FIG. 8 illustrates one form of the invention.
9 illustrates how the device of FIG. 8 generates a high voltage at the primary winding 15 of the transformer.
FIG. 10 is similar to FIG. 9, but shows three half cycles applied to the primary of the transformer.
FIG. 11 illustrates an overview of one form of the present invention.
FIG. 12 illustrates parameter values for one form of the invention.
FIG. 13 illustrates how the primary of the transformer is loaded by the parasitic capacitance.
[Explanation of symbols]
12 sine wave 13 primary side 14 transformer 15 primary winding 18 transformer 19 sine wave A1 amplifier A2 amplifier

Claims (7)

A high voltage stylus for a digital pad,
(A) a transformer having a pair of primary windings;
(B) means for supplying two different sinusoidal signals having a phase difference to the primary winding of the transformer;
A high-voltage stylus characterized by comprising The high voltage stylus according to claim 1, wherein a phase difference between the two sine wave signals is 180 degrees. The high voltage stylus according to claim 1 or 2, wherein a battery is mounted, an electric current flowing out of the battery is less than 4 milliamperes, and an amplitude value of an output voltage of the secondary conductor exceeds 30 volts. . The high voltage stylus according to claim 3, wherein the rated voltage of the battery is 3.6V and the power consumption is 15 milliwatts or less. A high voltage stylus device for a digital pad,
(A) means for generating a sine wave signal;
(B) first amplification means for amplifying the sine wave signal;
(C) inverter means for inverting the sine wave signal;
(D) second amplification means for amplifying an inverted signal of the sine wave signal;
(E) having a set of primary side conductors and a set of secondary side conductors, one of the primary side conductors being connected to the output of the first amplification means and the other being the output of the second amplification means. Connected transformer,
(F) a tip connected to the output of the secondary conductor;
A high-voltage stylus device comprising: 6. The high voltage stylus device according to claim 5, wherein a battery is mounted, a current flowing out of the battery is less than 4 milliamperes, and an amplitude value of an output voltage of the secondary side conductor exceeds 30 volts. The high voltage stylus device according to claim 6, wherein the rated voltage of the battery is 3.6V, and the power consumption is 15 milliwatts or less.

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