JPH07302153A - Coordinate detecting device - Google Patents

Abstract

PURPOSE:To eliminate the need for preparing any special amplifier nor A/D converter at the reception side despite the high frequency of the transmission side by preparing a local transmitter, a frequency mixer and a filter at the transmission side and before an A/D converter or a detector. CONSTITUTION:At the side of a reception circuit, a local transmitter 21 is prepared to transmit a signal of frequency f2 so as to set ¦f1-f2¦ at 20-100kHz with reception frequency f1, together with a frequency mixer 20 which mixes the voltage signal received from the transmitter 21 with the reception voltage signal and divides them into the frequency signals of f1-f2 and f1+f2, and a filter 22 which extracts the signal f1-f2. Then the amplified signal is mixed with the signal of f2 received from the transmitter 21 by the mixer 20, and only the signal of f1-f2 is extracted by the filter 22. This extracted beat-down signal is amplified by an intermediate frequency amplifier 23 and detected to undergo the digital conversion by an A/D converter 6' and then to undergo the coordinate arithmetic processing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a coordinate detecting device for exchanging radio waves between a tablet and a position indicator to input coordinate values on the tablet designated by the position indicator. .

[0002]

2. Description of the Related Art Conventionally, there has been known a coordinate detecting device for exchanging radio waves between a tablet and a position indicator such as an input pen or a cursor to input coordinate values on the tablet designated by the position indicator. There is. Now, one of conventional examples will be described with reference to FIG. In the figure, 9 is a loop coil arranged on a printed circuit board, and 11 is a position indicator including a tuning circuit having at least one coil and a capacitor and having a predetermined frequency as a tuning frequency. Reference numeral 1 is a high frequency AC power source having a frequency with which the position indicator is tuned. The frequency is, for example, 500 KHZ. Reference numeral 2 is an amplifier, and the amplified voltage is the switching device 1
It is applied to the loop coil 9 via 0 and 8. After a lapse of a predetermined period, the switching device 10 switches the high frequency amplifier 4,
It is switched to the receiving circuit side including the detector 5 and the A / D converter 6. A high-frequency amplifier 4 amplifies an induced voltage caused by the radio wave reflected from the position pointing device 11 by about 1000 times. Reference numeral 5 is a detector for detecting the signal obtained by the amplification. An A / D converter 6 digitizes the analog information value obtained by the detection. The A / D converter in this case may be one that can process an AC signal of about 5 KHZ. Reference numeral 7 denotes a processor, which performs predetermined arithmetic processing based on the digital information obtained from each of the loop coils to calculate the X coordinate and the Y coordinate on the tablet of the position indicator. In the case of this conventional example, the higher the tuning frequency is, the lower the values of L and C are. Therefore, for example, regarding a coil, its inductance, that is, its number of turns may be small, so that there is an advantage that the position indicator can be designed compactly. On the other hand, since the radio wave reflected from the position indicator is weak, the amplifier on the receiving side must be about 1000 times larger, and an amplifier that can obtain a large amplification factor at such a high frequency is expensive. There was a drawback.

FIG. 2 shows another conventional example, but the difference from the case of FIG. 1 is that the signal amplified on the receiving circuit side is directly converted into a digital signal by an A / D converter for detection processing. It is performed digitally by the processor (Japanese Patent Laid-Open No. 14701/1991).
2). In this case, there is a problem that the A / D converter must be able to process the AC signal of 500 KHZ because the amplified signal is not detected. An amplifier and an A / D converter corresponding to a high frequency have a problem that the higher the frequency is, the more difficult it is to design and eventually the cost becomes higher.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to avoid the use of special amplifiers and A / D converters on the receiving side even when the frequency on the transmitting side is high. It is to provide a coordinate detection device.

[0005]

In order to achieve the above object, the coordinate detecting apparatus of the present invention comprises a local oscillator and a frequency mixer (superimposing circuit) in front of an A / D converter or a detector on the receiving side. ) And a filter.

[0006]

According to the above construction, the induction voltage of about 500 KHZ obtained in the loop coil is amplified about 5 to 10 times, and the signal is transmitted from the local oscillator 450.
A signal having a frequency of f1 to f2 is combined with a signal having a frequency of KHZ (hereinafter, referred to as “frequency f2”) by a frequency mixer, and only signals having frequencies f1 to f2 are extracted by a filter, and the signal is passed through a detector or It is connected to the A / D converter without intervention.

Whether the signal is through the detector or not, the first stage amplifier on the receiving side has an amplification factor of 5
It may be about 10 to 10. A / D without a detector
When connected to the converter, the A / D converter is 50KH
Any frequency can be used as long as it can handle frequencies of about Z.

[0008]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 3 is a first embodiment of the present invention, which is an improvement of the conventional example of FIG. The difference from the comparison with FIG. 1 is that the amplification factor of the first-stage amplifier 4 ′ on the receiving side may be about 5 to 10 times. The signal amplified here is only 500 KHZ (hereinafter referred to as "frequency f1"), but is combined with the signal of frequency 450 KHZ (hereinafter referred to as "frequency f2") transmitted from the local oscillator 21 by the frequency mixer. Then, only the signal having the frequency of 50 KHZ (f1-f2) is extracted by the filter 22. This beat down signal (frequency 5
0KHZ) is amplified several hundred times by the intermediate frequency amplifier 23, detected, and then converted into a digital value by the A / D converter, and coordinate calculation processing is performed. Therefore, according to this embodiment, the first-stage amplifier on the receiving side can have a small amplification factor.

FIG. 4 shows a second embodiment of the present invention, which is an improvement of the conventional example shown in FIG. The difference from the comparison with FIG. 2 is that, as in the first embodiment, the amplification factor of the first stage amplifier 4'on the receiving side may be about 5 to 10 times. The signal amplified here is only 500 KHZ (hereinafter referred to as “frequency f1”), but the frequency of 450 KHZ transmitted from the local oscillator 21.
The signal (hereinafter referred to as "frequency f2") is combined in the frequency mixer 20, and then only the frequency of 50 KHZ (f1-f2) is extracted by the filter. This beat down signal (frequency 50 KHZ) is an intermediate frequency amplifier. After being amplified about 100 to 500 times by 23, it is not detected but converted into a digital value by the A / D converter and coordinate calculation processing is performed.The feature of this embodiment is that the received signal is not detected. In the case of A / D conversion, since the signal amplified by the intermediate frequency amplifier is 50 KHZ (f1-f2) as before, even if it is not detected, the A / D converter has a frequency of about 50 KHZ. Therefore, according to this embodiment, it is possible to use the receiving side first stage amplifier having a small amplification factor and Can be advantageously covered by it can correspond to a lower frequency A / D converter.

In the above two embodiments, the case where f2 has a frequency lower than f1 has been shown, but even if f2 is made higher than f1, beatdown to f2-f1 can be considered in the same way.

[0012]

As described above, according to the present invention,
The first-stage amplifier on the receiving side can be covered with a low amplification factor of about 1/100 compared to the conventional one, and when the received signal is A / D converted without detection, the A / D converter is Since it is possible to use one corresponding to a low frequency of about 1/10, there is an advantage that the design is easy and the cost can be reduced as a result.

[Brief description of drawings]

FIG. 1 An example of a conventional coordinate detection device

FIG. 2 is an example of a conventional coordinate detection device.

FIG. 3 is an example of a coordinate detection device of the present invention

FIG. 4 is an example of a coordinate detection device of the present invention.

[Explanation of symbols]

 1 high frequency oscillator 2 amplifier 4 high frequency amplifier 4'first stage amplifier 5 detector 6, 6'A / D converter 7 processor 8 terminal 9 loop coil 10 terminal 11 position indicator including tuning circuit 20 frequency mixing section 21 local oscillation Unit 22 Filter 23 Intermediate frequency amplifier

Claims (1)

[Claims] 1. A coordinate detection device for exchanging radio waves with a position indicator having a tuning circuit to detect a pointed position on a tablet designated by the position indicator, the receiving circuit side receiving the signal. | F1 to f when the frequency is f1
2 | is a local oscillator that transmits a signal of frequency f2 such that it is in the range of 20 KHZ to 100 KHZ, and the voltage signals transmitted from the local oscillator and the reception voltage signal are mixed to obtain frequencies of f1-f2 and f1 + f2. A frequency mixer that is separately generated into a signal and f1 of the signals that are separately generated
A coordinate detecting device provided with a filter for extracting a signal of -f2.