JPH08139583A - Touch key - Google Patents

Abstract

PURPOSE: To provide a touch key capable of detecting accurate key input even when diffused external light fluctuates corresponding to surrounding brightness. CONSTITUTION: Infrared pulse light emitted from a light emitting element 2 based on the drive signals 21 of a prescribed frequency outputted from a drive circuit 1 passes through a transparent body 3, is reflected on a reflector 4, passes through the transparent body 3 again, is received in a light receiving element 5 and outputted as reception signals 22. for the reception signals 22, DC bias components by the diffused external light are eliminated by a high-pass filter 6, they are amplified by an AC amplifier circuit 7 and then converted into DC signals 24 corresponding to the reception level of the received infrared light by an integration circuit 8 and the presence/absence of the key input are judged by a compared result with a prescribed threshold voltage by a discrimination circuit 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a touch key, and more particularly to emitting infrared light to a reflector such as a finger and receiving infrared light reflected by the reflector to detect the presence or absence of the reflector. By doing so, the present invention relates to a touch key that outputs a key input signal.

[0002]

2. Description of the Related Art Generally, a touch key of this type does not require a mechanically operating portion and can be made highly confidential, so that it is often used in various measuring instruments installed outdoors. FIG. 8 is a block diagram showing a configuration of a conventional touch key (for example, Japanese Patent Laid-Open No. 3-114316). In the figure, 51 is a modulator that outputs a predetermined drive signal 62 in response to a key scan signal 61, 52 is a light emitting element that emits infrared light based on the drive signal 62, 53 is a transparent body such as glass, and 54 Is a reflector such as a finger, 55 is a light receiving element that receives the infrared light reflected by the reflector 54 through the transparent body 53 and outputs a reception signal 63, and 56 is a reception signal 6
3 and the drive signal 62 are compared with each other, and the comparison unit 57 outputs the comparison result. The control unit 57 outputs the drive signal 61 and the key input signal 64 according to the comparison result from the comparison unit 56 (hereinafter, referred to as a control unit). , MPU).

FIG. 9 is a timing chart showing signals of respective parts of FIG. Now, the modulator 51 outputs a drive signal 62 having a predetermined pulse pattern in response to the key scan signal 61 from the MPU 57, and infrared light based on the drive signal 62 is emitted from the light emitting element 52. Here, the light emitting element 5
When there is a reflector 54 such as a finger near 2, the infrared light emitted from the light emitting element 52 and passing through the transparent body 53 such as glass is reflected by the reflector 54 and again passes through the transparent body 53. The light is received by the light receiving element 55, and the reception signal 63 is output.

This received light signal 63 is output by the comparison unit 56.
When the light beam detected by the light receiving element 55, which is sequentially compared with the drive signal 62 from the modulator 51, is the infrared light emitted from the light emitting element 52 and reflected by the reflector 54, the light from the light receiving element 55 is emitted. Since the received signal 63 and the drive signal 62 match, the comparison result indicating the match is output, while the light receiving element 5
When the light beam detected in 5 is the ambient light, the received signal 63 and the drive signal 62 do not match, so the comparison result indicating the match is not output, and the MPU 57 outputs the comparison result indicating the match from the comparison unit 56. In response, the key input signal 64 is output. In this way, the drive signal 62 by the comparison unit 56
The presence / absence of a key input is determined according to the coincidence between the received signal 63 and the received signal 63 to prevent malfunction due to ambient light.

[0005]

Therefore, in such a conventional touch key, whether the normal reflected light or the ambient light is judged is simply determined based on the comparison result of the pulse patterns. Since there is no means for compensating the pulse detection sensitivity of the light receiving element that fluctuates according to the change in the depth, it becomes difficult to detect the pulse accurately due to the change of day and night or the weather, and there is a possibility that erroneous detection may occur. It was FIG.
0 is an explanatory diagram showing the relationship between the ambient brightness and the received signal from the light receiving element, where (a) is a relatively dark environment with little ambient light, and (b) is a relatively bright environment with ambient light. It shows the case of many cases.

Generally, when an object is detected using infrared light, a visible light cut filter is provided in front of the light receiving element 55 to remove visible light, thereby suppressing the influence of ambient light. However, it is impossible to completely remove only visible light, and the unremoved visible light is detected by the light receiving element 55 as ambient light and is output as a leakage current. FIG. 10A shows a case such as at night, for example, in which the amount of ambient light is small, the leakage current from the light receiving element 55 is small, the crest value (amplitude) of the pulse synchronized with the drive signal 62 is sufficient, and the comparison unit 56 Thus, even when such a received signal 63 is simply compared with the threshold voltage VTH, a signal waveform comparable with the drive signal 62 can be obtained.

On the other hand, FIG. 10 (b) shows a case, for example, during the daytime, in which a large amount of ambient light causes a large leakage current from the light receiving element 55, which causes a DC bias voltage to generate a pulse with a threshold voltage. There is a problem in that a key waveform cannot be accurately detected because a signal waveform comparable to the drive signal 62 cannot be obtained because of deviation from VTH. The present invention is intended to solve such a problem, and an object of the present invention is to provide a touch key capable of detecting an accurate key input even when ambient light changes depending on ambient brightness.

[0008]

In order to achieve such an object, a touch key according to the present invention comprises a drive circuit for outputting a pulse-shaped drive signal having a predetermined frequency, and an infrared light modulated by the drive signal. A light-emitting element that emits light to a reflector such as a finger through a transparent body, and the infrared light that is provided adjacent to this light-emitting element, receives the infrared light reflected by the reflector through the transparent body, and outputs a reception signal A light-receiving element, a high-pass filter that removes the low-frequency component contained in the received signal and passes the modulation frequency component of infrared light, the amplitude of the AC signal output from this high-pass filter, and a predetermined threshold voltage And a discriminating circuit for discriminating the presence / absence of the reflector and outputting the discrimination result as a key input signal.

Further, the AC circuit from the high-pass filter has an integrating circuit for converting the AC signal from the high-pass filter into a DC signal by integrating the AC signal with a predetermined time constant, and a time constant sufficiently larger than the time constant of the integrating circuit. A base voltage integrating circuit that converts and outputs a base voltage signal by integrating the signal is provided, and the determining circuit compares the difference between the DC signal and the base voltage signal with a predetermined voltage value.
The presence or absence of a reflector is determined. Further, when the presence or absence of ambient light is detected from the received signal output from the light receiving element and the ambient light detection means for outputting the ambient light detection signal and the key input signal from the discrimination circuit indicate the presence of a reflector, the ambient light is detected. A logic circuit that refers to the light detection signal and outputs the key input signal as the key detection signal only when the disturbance light detection signal indicates that there is no disturbance light is provided.

Further, the disturbance light detecting means removes the modulation frequency component of the infrared light contained in the received signal from the light receiving element and outputs a direct current component, and the output from this low pass filter and a predetermined value. And a comparator circuit that outputs a disturbance light detection signal indicating the presence or absence of disturbance light by comparing with the threshold voltage of. In addition, a delay circuit for delaying a key input signal output from the determination circuit and indicating the presence of the reflector for a predetermined time and outputting the delayed signal to the logic circuit is provided. Further, it is provided with a means for stopping the emission of infrared light by the light emitting element when the ambient light is detected by the ambient light detecting means.

[0011]

Therefore, the infrared light emitted from the light emitting element is reflected by the reflector such as a finger through the transparent body, is again received by the light receiving element through the transparent body, and is output as a reception signal. The low-frequency component is removed by means of to become an AC signal, and the discrimination circuit compares the amplitude with a predetermined threshold voltage, and if the amplitude exceeds a predetermined threshold voltage, it is judged that there is a reflector. , A key input signal indicating that there is a key input is output.

[0012]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a touch key according to an embodiment of the present invention. In FIG. 1, 1 is a drive circuit that outputs a drive signal 21 composed of a pulse train of a predetermined frequency,
Reference numeral 2 is a light emitting element that emits infrared light based on the drive signal 21, 3 is a transparent body such as glass, and 4 is a finger of the operator or the like, and reflects infrared light from the light emitting element 2 that has passed through the transparent body 3. The reflector 5 is arranged adjacent to the light emitting element 2 and receives the infrared light reflected by the reflector 4 and passed through the transparent body 3 to output a reception signal 22, and 6 is a reception signal 22. A high-pass filter that passes the frequency component of the contained infrared light and removes a low-frequency component, and 7 is an AC amplifier circuit that amplifies the output from the high-pass filter 6 and outputs it as an AC signal 23.

Reference numeral 8 is an integrating circuit for integrating the AC signal 23 from the AC amplifying circuit 7 based on a predetermined time constant, and 9 is a comparison of the DC signal 24 from the integrating circuit 8 with a predetermined threshold voltage VTH. A discriminating circuit for discriminating the presence / absence of a reflector and outputting a key input signal 25 indicating the presence / absence of a key input.
FIG. 2 is a timing chart showing the signals of the respective parts in FIG. 1, and particularly shows the case where the ambient light is relatively large. In FIG. 2, 20 is the presence or absence of the reflector 4, 21 is a drive signal,
22 is a received signal, 23 is an AC signal, 24 is a DC signal, 2
Reference numeral 5 is a key input signal.

Next, the operation of the present invention will be described with reference to FIGS. If the reflector 4 is not present in the vicinity of the light emitting element 2 (OFF), the infrared light emitted from the light emitting element 2 based on the drive signal 21 is not reflected by the reflector 4 and therefore the transparent body 3 is used. A small amount of reflected infrared light is received by the light receiving element 5 and ambient light is received, and a DC bias voltage due to the ambient light is generated in the reception signal 22 output from the light receiving element 5, and thus a slight detection is performed. The infrared light being emitted has a raised waveform.

The received signal 22 is sent to the high-pass filter 6
After the low frequency component, that is, the direct current component, is removed at 1, the AC signal 23 is amplified by the alternating current amplifier circuit 7 and corresponds to the received infrared light, and is further integrated by the integrating circuit 8 to obtain the amplitude voltage of the alternating current signal 23, that is, The DC signal 24 indicates the reception level of infrared light. In this case, since the infrared light received by the light receiving element 5 is weak due to the reflection of the transparent body 3, its light receiving level is low. Therefore, the DC signal 24 has a level lower than the threshold voltage VTH of the determination circuit 9 and is determined to be "no key input", and the key input signal 25 is output at L level indicating "no key input".

Next, at time T0, when the reflector 4 approaches the vicinity of the light emitting element 2 (when ON), the light emitting element 2
Infrared light from is reflected by the reflector 4 and received by the light receiving element 5, has a DC bias voltage due to ambient light as described above, and has a larger amplitude than the infrared light reflected by the transparent body 3. 22 is output from the light receiving element 5. The received signal 22 has a direct-current component removed by a high-pass filter 6 and then amplified by an alternating-current amplifier circuit 7 to generate an alternating-current signal 2
3 and becomes the DC signal 24 after being integrated by the integrating circuit 8.

In this case, since the infrared light received by the light receiving element 5 has a remarkably large amplitude as compared with the infrared light reflected by the transparent body 3, the light receiving level thereof is high. Therefore, the DC signal 24 is the threshold voltage V of the discrimination circuit 9.
When the level becomes higher than TH, it is determined that "key input is present", and the key input signal 25 is H level indicating "key input is present".

In this way, the high pass filter 6
The DC bias voltage due to the ambient light is removed from the reception signal 22 output from the light receiving element 5, and the AC signal 23 is converted into a DC signal 24 having a value corresponding to the amplitude voltage, that is, the reception level of infrared light by the integrating circuit 8. After the conversion, the discrimination circuit 9 compares the threshold voltage VTH with the threshold voltage VTH. Therefore, the infrared light reflected by the reflector 4 can be detected more reliably regardless of the presence or absence of ambient light, and the accuracy can be improved. It is possible to perform various key input determinations. In the above description, the case where the integrating circuit 8 generates the DC signal 24 indicating the reception level of infrared light from the reception signal 22 has been described. The DC signal 24 may be generated by a low-pass filter that removes the component, and the same operational effect as described above can be obtained.

Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a block diagram showing the configuration of the touch key according to the second embodiment of the present invention, in which the same or equivalent parts as those in the above description (see FIG. 1) are designated by the same reference numerals. . In FIG. 3, reference numeral 11 is a base voltage integration circuit that integrates the AC signal 23 from the AC amplification circuit 7 and outputs a base voltage signal 26 with a time constant sufficiently larger than the integration time constant of the integration circuit 8.
2, the DC signal 24 from the integrating circuit 8 is the base voltage signal 2
When the voltage value becomes equal to or higher than the predetermined voltage value VD from No. 6, the determination circuit 1 determines that "key input is present" and outputs the key input signal 25.
It is 2.

FIG. 4 is a timing chart showing the signals of the respective parts in FIG. 3, and particularly shows the case where the amount of ambient light is relatively large. In FIG. 4, the above description (see FIG. 2)
The same or equivalent parts as those of
Is the base voltage signal. If the reflector 4 is not present near the light emitting element 2 (if OFF), the infrared light emitted from the light emitting element 2 based on the drive signal 21 is not reflected by the reflector 4.
Since a small amount of infrared light reflected by the transparent body 3 is received by the light receiving element 5 and ambient light is received by the light receiving element 5, the high pass filter 6 causes the ambient light due to the ambient light as described above (see FIG. 1). After the DC bias voltage is removed, it is output as an AC signal 23 corresponding to the infrared light amplified and received by the AC amplifier circuit 7.

Here, the AC signal 23 is supplied to both the integrator circuit 8 and the base voltage integrator circuit 11, and the integrator circuit 8 indicates the received light level of infrared light in the same manner as described above.
4 and the base voltage signal 26 by the base voltage integration circuit 11 having a time constant sufficiently larger than the integration time constant of the integration circuit 8, for example, 10 times or more.
Is output as In this case, since the infrared light received by the light receiving element 5 is weak due to the reflection of the transparent body 3, its light receiving level is low, and since the light receiving level does not vary, the DC signal 24 and the base voltage signal are There is almost no difference from 26.

Therefore, since the difference between the DC signal 24 and the base voltage signal 26 is smaller than the voltage value VD, the discrimination circuit 9
Is determined as “no key input”, and the key input signal 25
Outputs L level indicating "no key input". Next, at time T0, when the reflector 4 approaches the vicinity of the light emitting element 2 (when ON), infrared light from the light emitting element 2 is reflected by the reflector 4 and received by the light receiving element 5, Similarly, a reception signal 22 having a DC bias voltage due to ambient light and having an amplitude larger than that of infrared light due to reflection from the transparent body 3 is output from the light receiving element 5, and the high-pass filter 6 removes the DC component, and then the AC signal. The amplified signal is amplified by the amplifier circuit 7 into an AC signal 23, which is supplied to the integrating circuit 8 and the base voltage integrating circuit 11.

In this case, since the infrared light received by the light receiving element 5 has a remarkably large amplitude as compared with the light reflected by the transparent body 3, the received light level is high and the AC signal 23 Since the amplitude is also large, the DC signal 24 from the integrating circuit 8 having a relatively small time constant immediately exhibits a high voltage value. On the other hand, in the base voltage integrating circuit having a sufficiently large time constant, the voltage gradually increases in response to the input of the AC signal 23 having a large amplitude.

Therefore, when the difference between the DC signal 24 and the base voltage signal 26 becomes large and becomes equal to or higher than the voltage value VD, the discrimination circuit 9 discriminates that "key input is present",
As the key input signal 25, the H level indicating "key input is present" is output. Furthermore, at time T1, when the reflector 4 is no longer present (when OFF),
When the amplitude of the AC signal 23 becomes small, the DC signal 24 from the integrating circuit 8 also exhibits a low voltage value in response to this, and when the difference between the DC signal 24 and the base voltage signal 26 becomes lower than the voltage value VD. Then, the discriminating circuit 9 discriminates "no key input", and the L level indicating "no key input" is outputted as the key input signal 25.

As described above, the base voltage integrating circuit 1 having a sufficiently large time constant as compared with the integrating time constant of the integrating circuit 8.
1, the AC signal 23 is integrated and the base voltage signal 26
And the discrimination circuit 12 causes the base voltage signal 2
When the difference between the DC signal 24 and the DC signal 24 becomes larger than the predetermined voltage value VD, it is determined that "key input is present". Therefore, the brightness of the light emitting element 2 decreases due to the temperature change, the secular change, or the transparent body 3 Even when the level of the infrared light received by the light receiving element 5 is reduced due to dirt on the base voltage signal 26, the base voltage signal 26 fluctuates accordingly, and the change of the DC signal 24 output from the integrating circuit 8 is suppressed. It becomes possible to detect with higher accuracy, and it is possible to realize a touch key that can automatically respond to the installation environment and changes over time and can perform accurate key input detection.

Next, a third embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a block diagram showing the configuration of a touch key according to a third embodiment of the present invention, in which the same or equivalent parts as those in the above description (see FIGS. 1 and 3) are designated by the same reference numerals. There is. In FIG. 5, 13 is a switch for controlling the drive signal 21 input to the light emitting element 2, 14 is a low-pass filter for outputting a DC component from which a high frequency component included in the received signal 22 from the light receiving element 5 is removed, and 15 is a low pass filter. The low-pass filter 14 is a comparison circuit that outputs the ambient light detection signal 27 when the output from the filter 14 exceeds a predetermined threshold voltage.
The ambient light detection means is constituted by the comparator circuit 15 and the comparison circuit 15.

Reference numeral 16 is a key input signal 2 from the discrimination circuit 12.
5, a delay circuit that outputs a delay signal 28 delayed from the rising edge of 5; and 17 denotes a case where the ambient light detection signal 27 indicates “no ambient light” and the delay signal 28 indicates “key input present”, Key detection signal 29 indicating "key input present"
Is a logic circuit that outputs. 6 and 7 are timing charts showing the signals of the respective parts in FIG.
Shows a case where the amount of ambient light is relatively large, and FIG. 7 shows a case where the ambient light is relatively small. In FIGS. 6 and 7, the same or equivalent parts as those in the above description (see FIGS. 2 and 4) are denoted by the same reference numerals, 27 is a disturbance light detection signal, 28 is a delay signal, 29 is a key detection signal, and 30 is Indicates the presence or absence of ambient light that is suddenly generated.

In FIG. 6, which shows a case where the ambient light is relatively large, when the reflector 4 is not present near the light emitting element 2 (OF
In the case of F), the ambient light is received by the light receiving element 5, so the low-pass filter 14 and the comparison circuit 15 detect this and the ambient light detection signal 27 becomes H level, whereby the switch 13 is opened. The drive signal 21 to the light emitting element 2 is stopped. Therefore, infrared light is not emitted from the light emitting element 2, the key input signal 25 output from the determination circuit 12 becomes L level, and the logic circuit 17
The key detection signal 29 from is also at the L level indicating "no key input".

At time T0, the reflector 4 is turned on by the light emitting element 2
When it is close to the vicinity (when it is ON), the disturbance light to the light receiving element 5 adjacent to the light emitting element 2 is blocked by the reflector 4, and the disturbance light detection signal 2 from the comparison circuit 15 is generated.
7 is inverted to L level, the switch 13 is turned on, and the drive signal 21 is input to the light emitting element 2. This allows
Infrared light is emitted from the light emitting element 2, and the light reflected by the reflector 4 is received by the light receiving element 5, and the key input signal 25 from the discrimination circuit 12 is changed from the L level to the H level in the same manner as described above (see FIG. 3). Stand up.

The key input signal 25 is output by the delay circuit 16 as a delay signal 28 whose rising edge is delayed by a predetermined time td, and the logic circuit 17 outputs the delay signal 2
In response to the rising edge of 8, the disturbance light detection signal 27 is referred to, and since this is at the L level indicating "no disturbance light", the H level key detection signal 29 indicating "key input" is set to any value. It will be output for a period.

Further, when a sudden disturbance light stronger than the disturbance light constantly input at time T1 is generated (when it is ON), this is received by the light receiving element 5, and the DC signal 24 from the integrating circuit 8 is received. Even if it changes and is erroneously detected by the discrimination circuit 12, the disturbance light detection signal 27 always indicates the H level due to the disturbance light that is always input. Therefore, the logic circuit 17 causes the key output from the discrimination circuit 12 to be displayed. Input signal 2
It is determined that the delay signal 28 input according to 5 does not indicate a normal key input, and the L level indicating "no key input" is output as the key detection signal 29.

On the other hand, in FIG. 7 showing a case where the amount of ambient light is relatively small, the ambient light is not received by the light receiving element 5, and the ambient light detection signal 27 output from the comparison circuit 15 becomes L level. Is turned on and the light emitting element 2
The drive signal 21 is input to. Therefore, when the reflector 4 does not exist near the light emitting element 2 (when it is OFF), the infrared light emitted from the light emitting element 2 is not received by the light receiving element 5, and the key input signal 25 output from the determination circuit 12 is output. Is at the L level, and the key detection signal 29 from the logic circuit 17 is also at the L level indicating "no key input".

Here, at time T0, when the reflector 4 approaches the vicinity of the light emitting element 2 (when ON), the infrared light from the light emitting element 2 is reflected by the reflector 4 and received by the light receiving element 5. The determination circuit 12 determines that “key input is present”, the key input signal 25 becomes H level, and the delay circuit 16
Delay signal 2 whose rising edge is delayed by a predetermined time td due to
8 is input to the logic circuit 17. In response to this, the logic circuit 17 refers to the ambient light detection signal 27, and since this is the L level indicating "no ambient light", the H level indicating "key input" is arbitrarily set as the key detection signal 29. Will be output during the period.

Further, when a sudden disturbance light stronger than the disturbance light constantly input at time T1 is generated (when ON), this is received by the light receiving element 5, and the DC signal 24 from the integrating circuit 8 is received. Even if it changes and is erroneously detected by the determination circuit 12, the low-pass filter 14 and the comparison circuit 1
The ambient light is detected by 5, and the ambient light detection signal 27 becomes H.
The delay signal 28 becomes the level and the key input signal 25 from the discrimination circuit 12 is delayed by the delay circuit 16 for the time td.
When the disturbance light detection signal 27 is already at the H level indicating “there is disturbance light”, the logic circuit 17 outputs the key detection signal 29 indicating “no key input” as H. The level is output for an arbitrary period.

As described above, when the ambient light is not detected by providing the low-pass filter 14 and the comparing circuit 15 for detecting the ambient light and the delay circuit 16 for delaying the key input signal 25 from the discriminating circuit 12, Only
Since the key input signal 25 is determined to be a normal output and the key detection signal 29 is output, it is possible to reliably detect the key input even in an installation place where unexpected ambient light is generated. It will be possible. Further, the switch 1 for controlling the drive signal 21 to the light emitting element 2 according to the ambient light detection signal 27.
3 is provided, the emission of infrared light is stopped when ambient light is detected, and the infrared light is emitted only when there is a possibility that the reflector 4 is present. It becomes possible to reduce.

[0036]

As described above, according to the present invention, a high-pass filter is provided to remove low-frequency components contained in a received signal from a light receiving element, thereby removing a DC bias voltage due to disturbance light to remove an AC signal. And the discrimination circuit
Since the presence or absence of the reflector is determined by comparing the amplitude of the AC signal with the threshold voltage, the infrared light reflected by the reflector can be detected more reliably regardless of the presence or absence of ambient light. Therefore, it becomes possible to perform accurate key input determination.

Further, it has an integrating circuit for integrating the AC signal with a predetermined time constant and a time constant sufficiently larger than the time constant of this integrating circuit, and by converting the AC signal from the high-pass filter into a base voltage signal. The base voltage integrating circuit for outputting is provided, and the presence or absence of the reflector is judged by comparing the difference between the DC signal and the base voltage signal with a predetermined voltage value by the judging circuit. Even if the level of infrared light received by the light receiving element decreases due to a decrease in brightness due to changes, aging, or stains on the transparent body, the base voltage signal will fluctuate accordingly. It becomes possible to detect changes in the output DC signal more accurately,
It becomes possible to realize a touch key that can automatically respond to the installation environment and changes over time and can detect the key input accurately.

Further, an ambient light detecting means for detecting the presence or absence of ambient light from the received signal output from the light receiving element and outputting the ambient light detection signal is provided, and the key input signal from the discrimination circuit is reflected by the logic circuit. When the presence of the body is indicated, the ambient light detection signal is referred to, and the key input signal is output as the key detection signal only when the ambient light detection signal indicates that there is no ambient light. Even in an installation place where ambient light is generated, it is possible to reliably detect a key input. Furthermore, as ambient light detection means,
The low-pass filter removes the modulation frequency component of infrared light contained in the received signal from the light receiving element, and the comparator circuit compares it with a predetermined threshold voltage to determine the presence or absence of ambient light. Therefore, the ambient light can be detected more accurately.

Further, since the delay circuit delays the key input signal indicating the presence of the reflector output from the discriminating circuit and outputs the delayed key input signal to the logical circuit, a stable discriminating process can be performed in the logical circuit. Is possible. In addition, when the ambient light is detected by the ambient light detection means,
Since the emission of the infrared light by the light emitting element is stopped, the infrared light is emitted only when there is a possibility that the reflector is present, and the power consumption is reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of a touch key according to an exemplary embodiment of the present invention.

FIG. 2 is a timing chart of each part of the embodiment shown in FIG.

FIG. 3 is a block diagram of a touch key according to a second embodiment of the present invention.

FIG. 4 is a timing chart of each part of the embodiment shown in FIG.

FIG. 5 is a block diagram of a touch key according to a third embodiment of the present invention.

FIG. 6 is a timing chart in each part of the embodiment shown in FIG.

FIG. 7 is another timing chart in each part of the embodiment shown in FIG.

FIG. 8 is a block diagram showing a conventional touch key.

9 is a timing chart in each part of the conventional example shown in FIG.

FIG. 10 is an explanatory diagram showing a relationship between ambient brightness and a received signal from the light receiving element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Driving circuit, 2 ... Light emitting element, 3 ... Transparent body, 4 ... Reflector, 5 ... Light receiving element, 6 ... High pass filter, 7 ... AC amplification circuit, 8 ... Integration circuit, 9, 12 ... Discrimination circuit, 11 ... Base voltage integration circuit, 13 ... Switch, 14 ... Low-pass filter (disturbance light detection means), 15 ... Comparison circuit (disturbance light detection means), 16 ... Delay circuit, 17 ... Logic circuit, 21 ... Drive signal, 22 ... Received signal , 23 ... AC signal, 24 ... DC signal, 25 ... Key input signal, 26 ... Base voltage signal, 2
7 ... Ambient light detection signal, 28 ... Delay signal, 29 ... Key detection signal.

Claims (6)

[Claims] 1. A drive circuit which outputs a pulsed drive signal of a predetermined frequency, a light emitting element which emits infrared light modulated by the drive signal to a reflector such as a finger through a transparent body, and this light emission An infrared light that is provided adjacent to the element, receives the infrared light reflected by the reflector through the transparent body, and outputs a reception signal, and removes a low-frequency component included in the reception signal, The presence or absence of the reflector is determined by comparing the amplitude of the alternating-current signal output from the high-pass filter with a high-pass filter that passes the modulation frequency component of the infrared light and a predetermined threshold voltage. A touch key comprising: a determination circuit that outputs a result as a key input signal. 2. The touch key according to claim 1, wherein the AC signal from the high-pass filter is integrated by a predetermined time constant to be converted into a DC signal and output, and an integration circuit that is sufficiently larger than the time constant of the integration circuit. And a base voltage integrating circuit having a time constant and converting and outputting the base voltage signal by integrating the AC signal from the high-pass filter, wherein the determination circuit is a difference between the DC signal and the base voltage signal and a predetermined value. A touch key characterized in that the presence or absence of the reflector is judged by comparing with a voltage value. 3. The touch key according to claim 2, wherein the ambient light detecting means for detecting the presence or absence of ambient light from the reception signal output from the light receiving element and outputting the ambient light detection signal, and the discrimination circuit. When the key input signal indicates that there is a reflector, the ambient light detection signal is referred to, and only when the ambient light detection signal indicates that there is no ambient light, the key input signal is output as the key detection signal. A touch key including a logic circuit. 4. The touch key according to claim 3, wherein the ambient light detection unit removes a modulation frequency component of the infrared light included in a reception signal from the light receiving element and outputs a DC component. A touch key comprising: a filter; and a comparison circuit that outputs a disturbance light detection signal indicating presence or absence of disturbance light by comparing an output from the low-pass filter with a predetermined threshold voltage. 5. The touch key according to claim 3, further comprising a delay circuit that delays a key input signal, which is output from the determination circuit and indicates a presence of a reflector, for a predetermined time and outputs the delayed signal to the logic circuit. Touch key. 6. The touch key according to claim 3, wherein when ambient light is detected by the ambient light detecting means,
A touch key comprising means for stopping the emission of infrared light by the light emitting element.