JPH0758704A - Optical communication control unit - Google Patents

Abstract

PURPOSE:To prevent a unit, equipped with an optical transmitting means including a light emitting element and an optical receiving means including a light receiving element, from causing a communication error even if the source voltage varies or if the distance between transmission and reception becomes long and to improve the reliability by performing constant-current control over a current for making the light emitting element illuminate at the time of transmission. CONSTITUTION:The optical transmission means consists of a communication control LSI 1, a buffer 2, an operational amplifier 3, a transistor(TR) 4, the light emitting element 5, and a Zener diode 6. Then the operational amplifier 3 is provided between the base and emitter of the TR 4 which drives the light emitting element 5 to constitute a constant-current circuit which makes the photocurrent, flowing to the light emitting element 5, constant by providing negative feedback. Namely, the constant- current control over the current making the light emitting element 5 illuminate is performed at the time of transmission, so even if the source voltage VCC varies, the light output of the light emitting element 5 becomes constant. Further, the output voltage of the light receiving element is compared with a reference voltage which is made constant and data are outputted. Therefore, even if the source voltage VCC varies, the data which are reproduced have no variation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication control device for various information devices having an optical communication function as one of wireless communication, and more particularly to an optical communication control device suitable for battery-powered portable information devices. .

[0002]

2. Description of the Related Art In recent years, devices in which information devices communicate with each other via wireless communication means have become widespread. Wireless communication has recently attracted attention as a portable information device because it does not require a transmission path. In particular, as one of the wireless communication means, in addition to the one using electromagnetic waves, attention is paid to optical communication using light. This is different from the optical communication using an optical fiber. The light emitted from the element is transmitted to the light receiving element on the receiving side through the air. That is, under a short distance and under a condition where the light beam is not blocked by another object or the like, two communicating information devices are opposed to each other for communication.

FIG. 5 is an overall configuration diagram of a handheld computer which is one of the above-mentioned information equipments and which has a conventional optical communication means to which the present invention is applied. In the figure, 2
2 is a CPU, 23 is a memory, 24 is a keyboard, 20 is an optical communication control device, 21 is a communication control device other than optical communication, 2
Reference numeral 5 is a printer, and 26 is a display device. With the handheld computer having such a configuration, for example, the data input from the keyboard 24 or the data processed by the CPU 22 is sent to the optical communication control device 20, and the above-mentioned data and the like are transmitted by the optical transmission means in the optical communication control device 20 as described later. The flashing optical signal is transferred to the opposite information device based on the. The facing information equipment is provided with an optical receiving means as will be described later, and receives the transferred data. Further, the communication control device 20 is provided with the same optical receiving means as the above-mentioned opposite information equipment, receives the data transferred from the opposite information equipment provided with the same optical transmitting means as the above-mentioned optical transmitting means, and receives the received data. Is CP
The display device 26 and the printer 25 are processed by the U22.
Is output to. That is, information is exchanged with each other via the optical communication means, and required data is transmitted and received.

FIG. 6 is a circuit diagram showing a part of an optical transmitting means and an optical receiving means incorporated in a conventional communication control device. In the figure, 27 is an optical transmission means, which includes a communication control LSI 31, a buffer 32, a transistor 34, and a light emitting element 35 such as a light emitting diode. In this configuration, when a bit string is output from the communication control LSI 31 based on the data, a high potential or low potential signal is input to the buffer 32 according to the bit value. In response to the input, when the output of the buffer 32 is now set to the “High” level, the transistor 34 is turned on, the current supplied from Vcc flows through the light emitting electron 35, and outputs light.

28 is a light receiving means, which is a light receiving element 41 such as a phototransistor, a comparator 42, and a buffer 4.
3 and a communication control LSI 31, the communication control LSI is the same as the optical transmission means. In this structure, when the light receiving element such as the phototransistor receives light, the resistance value between the anode and the cathode changes, and V
The current supplied from cc is the resistance R depending on the amount of received light.
41 and the light receiving element 41. Therefore, that is, when the amount of light emission is large, the current flowing through the light receiving element is large, and the voltage input to the comparator 42 is low. Therefore, the-input level of the comparator 42 changes according to the amount of received light, and the-input level of the comparator is Vcc.
Is compared with a reference voltage obtained by being divided by resistors R42 and R43, the waveform is shaped into a high voltage or a low voltage according to the magnitude relation between the two, and the output is input to the communication control LSI 31 via the buffer 43.

[0006]

However, in the above-mentioned conventional optical transmitting means shown in FIG. 6, the optical output is V as shown in FIG.
The current (photocurrent) flowing through the light emitting element fluctuates as compared with cc. If the optical output fluctuates in the direction of decreasing, the amount of light on the receiving side becomes insufficient, which may cause a communication error. Especially for portable information devices such as handheld computers, Vcc
Is supplied from the battery, Vcc
The rate of occurrence of communication error increases because the rate of communication error increases.

Similarly, in the light receiving means, the voltage fluctuates in comparison with the reference voltage Vcc of the comparator 42. Therefore, the comparator output (received data) fluctuates as shown in FIG. 8 and a communication error may occur. . When the power supply voltages on the transmitting side and the receiving side overlap in this way, the occurrence rate of communication errors increases significantly. This tendency is particularly remarkable in portable information devices. Furthermore, in the above-mentioned conventional technique, since the light output of the light emitting element is constant regardless of the length of the distance between the transmitter and the receiver, if the distance between the transmitter and the receiver becomes long, the amount of received light decreases and a communication error occurs.

[0008]

SUMMARY OF THE INVENTION The present invention solves the problems of the prior art as described above, prevents the occurrence of communication errors due to the fluctuation of the power supply voltage Vcc even if the distance between the transmitting and receiving sides becomes long, and achieves highly reliable communication control. The purpose is to provide a device.

[0009]

In order to achieve this object, the present invention provides a communication control device including an optical transmitter including a light emitting element and an optical receiver including a light receiving element,
At the time of transmission, the current for causing the light emitting element to emit light is controlled to a constant current. Further, on the receiving side of the communication control device provided with the light transmitting means including the light emitting element, and the light receiving means including the light receiving element, the output voltage of the light receiving element,
It is characterized in that data is reproduced by comparing the reference voltages that have been made constant.

Further, in the communication control device provided with the light transmitting means including the light emitting element and the light receiving means including the light receiving element, the plurality of light emitting elements and the means for selectively driving the arbitrary number of the light emitting elements among the light emitting elements. With the same signal source,
It is characterized in that the above-mentioned arbitrary number of light emitting elements are selectively driven. Furthermore, in the above, when a communication error occurs or the communication error rate exceeds a predetermined value, a plurality of light emitting elements are driven. Furthermore, in a communication control device provided with a light transmitting means including a light emitting element, and a light receiving means including a light emitting element, a means for changing a current for causing the light emitting element to emit light is provided, and depending on a situation of a communication error,
It is characterized in that the current is changed.

[0011]

During transmission, the current for causing the light emitting element to emit light is controlled to a constant current, so that the light output of the light emitting element becomes constant even if the power supply voltage Vcc fluctuates. Further, since the data is reproduced by comparing the output voltage of the light receiving element with the reference voltage that has been made constant, the reproduced data does not change even if the power supply voltage Vcc changes. Furthermore, since a plurality of light emitting elements and means for selectively driving any number of the light emitting elements among the light emitting elements are provided and the same number of light emitting elements can be selectively driven by the same signal source, the distance between transmission and reception is long. Thus, when the amount of received light decreases and a communication error occurs or the communication error rate exceeds a predetermined value, the total optical output can be increased. Furthermore, a means for changing the current for changing the light emitting element is provided, and the current can be changed according to the situation of the communication error, so that the distance between the transmitting and receiving becomes long and the received light amount decreases, The light output can be increased when a communication error occurs or when the communication error rate exceeds a predetermined value.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a circuit diagram showing an embodiment of an optical transmission means of an optical communication control device according to the present invention. In the figure, 1 is a communication control device LSI, 2 is a buffer, 3 is an operational amplifier, 4 is a transistor, 5 is a light emitting element, and 6 is a Zener diode. The feature of this circuit is that the operational amplifier 3 is provided between the base and the emitter of the transistor 4 for driving the light emitting diode (light emitting element) to thereby form a constant current circuit for negative feedback to make the photocurrent passing through the light emitting element 5 constant. That is the point.

According to this configuration, when the communication control LSI 1 outputs a bit string based on the data, the high potential or low potential signal is input to the buffer 32 according to the bit value. Considering the case where the output goes to the “Low” level, the base voltage of the transistor 4 goes to the “Low” level regardless of the output level of the operational amplifier 3, so that the transistor 4 is turned off, so that no photocurrent flows. On the other hand, when the output of the buffer 2 becomes “High” level, the base voltage of the transistor 4 becomes “High” level, the transistor 4 is turned on, and the photocurrent passes through the light emitting element, the transistor 4, and the resistor R1. Flowing. At this time, when the photocurrent increases due to the presence of R1, the terminal voltage of the resistor R1 rises, but since this voltage is supplied to the negative input of the operational amplifier 3, negative feedback is applied and, for example, the current flowing through R1 due to fluctuation of Vcc. Is increased, the-input of the operational amplifier 3 is increased and the input voltage of the operation lamp is decreased, and its output is decreased.
Therefore, the base current of the transistor 4 decreases and the output current of the transistor 4 decreases. On the contrary, when the current flowing through R1 decreases, the-input of the operational amplifier 3 decreases and the input voltage of the operational amplifier increases, so that the output increases,
Therefore, the base current of the transistor 4 increases and the output current of the transistor 4 increases. As is well known, since the amplification factor of the operational amplifier 3 is sufficiently large, the operational amplifier 3 operates in a balanced state in which the voltage difference between the two input terminals of the operational amplifier 3 becomes almost zero. That is, the voltage at the-input terminal of the operational amplifier 3 becomes the -constant voltage V _A , and therefore the current flowing through R1 becomes V _A / R1 regardless of Vcc, and the current flowing through the light emitting element also becomes almost V _A / R1.

The + input terminal voltage V _{A of the} operational amplifier is V
As shown in FIG. 1, a zener diode 6 or the like is used to make a constant voltage so as not to vary with cc. As described above, if the current flowing through the light emitting element is made constant at the time of turning on regardless of the change in Vcc, the light output can be made constant against the change in the power supply voltage of the battery or the like.

Next, referring to FIG. 2, a method of reducing the error occurrence at the time of data demodulation by the light receiving element by keeping the reference voltage of the comparator of the light receiving means constant against the fluctuation of Vcc will be described. FIG. 2 is a diagram showing an example of a light receiving element side circuit according to the present invention. In the figure, 11 is a light receiving element, which is composed of, for example, a phototransistor.
Is a comparator, 13 is a buffer, R13 is a resistor, 14
Is a Zener diode. When light is received by a light receiving element such as a phototransistor, a current supplied from the constant voltage source Vc flows through the resistor R11 and the light receiving element 11 according to the amount of received light. The output of the light receiving element (phototransistor) 11 is one input terminal V of the comparator 12.
It is connected to i- and compared with the reference voltage V _B input to the other input terminal +. The reference voltage V _B is made constant by the Zener diode 14 and the resistor R13. Therefore, even if Vcc fluctuates, the reference voltage V _B does not fluctuate, and the output level of the comparator 12 depends only on the value of the received light amount. If the received light amount is a predetermined value or more, Vi− is V _B.
Below, the output of the comparator 12 becomes “High”, and its value is passed through the buffer 13 to the communication control LSI 1
Entered in.

FIG. 3 shows another embodiment of the communication control apparatus according to the present invention, showing an optical transmission means capable of automatically changing the output light quantity. In FIG. 3, 16
Is an AND gate, 2a and 2b are buffers 4a and 4b, and transistors 5a and 5b are light emitting elements such as light emitting diodes. The optical transmission means shown in this example can normally operate only the light emitting element 5a. That is, normally, the signal "LED2 ON" for setting the light emitting element 5b in the figure to the operable state is set to "Low", and the buffer 2b, the transistor 4b, and the light emitting element 5b are not operated. On the other hand, when a communication error caused by the optical transmission means is detected by a known technique, the above-mentioned “LED2 ON” is set to “High” to enable the transistor 4b. When a data bit string is output from the communication control LSI 1 in this state, the transistor 4a is turned on / off and the light emitting element 5a is turned on / off via the buffer 2a. In phase,
The transistor 4b is turned on / off via the AND gate 16 and the buffer 2b, and the light emitting element 5b is also turned on / off. Therefore, if the light emitting element 5a and the light emitting element 5b are provided close to each other, it is equivalent to one light source outputting twice as much light.

According to the above-described embodiment, the amount of received light is reduced as the distance between the transmitter and the receiver is increased, which has the effect of eliminating the problem that a communication error occurs. That is, after the communication error occurs and the'LED2 ON 'signal becomes'High' in the above, the'High 'state is maintained until the communication with the communication partner at that time is completed. In addition, when a communication error occurs once in the above, 'LE
Instead of immediately setting the D2 ON 'signal to'High',
"LED2ON" when the communication error rate exceeds the specified value
It is also possible to set the signal to “High”. Furthermore, in the above-mentioned embodiment, the case where two light emitting elements and their driving systems are provided in parallel has been shown, but it is not necessary to explain that they can be similarly realized even when the number of them is three or more. . In this case, for example, in the first communication error, only two generating elements are made operable, and when the communication error is still not resolved, the new light emitting elements are made operable one after another depending on the degree of the communication error. You may control so that the number of the light emitting elements driven to may be increased.

FIGS. 4A and 4B are circuit diagrams showing another embodiment of the present invention. In this example, in the above, the photocurrent flowing through the light emitting element is changed according to the situation of the communication error. Is. This is an example in which three types of current control circuits having different values are provided, and the light output is made constant at each value by making the current values of the above-mentioned constant current circuit different values. That is, as shown in FIG. 7A, the constant voltages VAa, VAb, and VAc obtained by the Zener diodes 6a, 6b, and 6c having different Zener voltages are applied to the + input terminal of the operational amplifier 3 via the respective switching circuits 17. The output of the operation lamp 3 supplied and fed back from the operational amplifier 3 is input to the base of the light emitting diode current control transistor 4. In this circuit, the operation is performed in accordance with the situation of the communication error, and any one of the selection terminals SLI1 to SLI1 of the switching circuit 17 of FIG.
gh 'signal,' Low 'to the terminal which is not selected
Signal is applied, only the switching circuit to which the potential of “High” is applied is turned on, and the selected voltage is supplied to the operational amplifier. Therefore, a current according to the selected voltage flows through the light emitting element, and the amount of light emission can be arbitrarily selected. FIG. 4B shows the details of the switching circuit shown in FIG. It goes without saying that the amount of light emission can be changed by changing the emitter resistance R1 of the light emitting element control transistor 4 in which V _A is changed in the above embodiment.
Further, the method of changing the photocurrent is not limited to the constant current circuit.

[0019]

As described above, according to the present invention,
Even if the power supply voltage Vcc fluctuates, the light output of the light emitting element can be kept constant, and the output voltage of the light receiving element is compared with a reference voltage that has been made into a constant voltage to reproduce the data. Even if the voltage Vcc fluctuates, the reproduced data waveform becomes a predetermined one. Further, even when the distance between the transmitting and receiving sides becomes long and the received light amount decreases, the emitted light amount can be increased to compensate for it. Further, when a communication error occurs, or when the communication error rate exceeds a predetermined value, the communication error can be eliminated by increasing the optical output, so that a highly reliable optical communication control device can be realized. Great effect.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an optical transmission means of an optical communication control device according to the present invention.

FIG. 2 is a circuit diagram showing an embodiment of an optical receiving means of the optical communication control device according to the present invention.

FIG. 3 is a circuit diagram showing another embodiment of the optical transmission means of the optical communication control device according to the present invention.

FIG. 4 is a circuit diagram showing another embodiment of the optical transmission means of the optical communication control device according to the present invention, in which (a) is an overall circuit diagram,
(B) is a figure which shows the specific example of a switching circuit.

FIG. 5 is an overall configuration diagram showing an example of an information device to which the present invention is applied.

FIG. 6 is a circuit diagram showing an example of an optical transmission unit and an optical reception unit of a conventional optical communication control device.

FIG. 7 is a diagram for explaining a problem to be solved by the present invention and is a characteristic diagram showing a relationship between a current and a light emission amount.

8A and 8B are diagrams for explaining a problem to be solved by the present invention, and are waveform diagrams showing a relationship between a reference voltage on the receiving side and a demodulation waveform.

[Explanation of symbols]

1 communication control LSI, 2 buffer, 3 operational amplifier,
4 transistors, 5 light emitting elements, 6 Zener diodes, 11 light receiving elements, 12 comparators, 13 buffers, 14 Zener diodes, 16 AND gates, 17 switching circuits, 20 communication control devices.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H04B 10/04 10/06 10/105 10/10 10/22

Claims (5)

[Claims] 1. An optical communication control device comprising an optical transmitter including a light emitting element and an optical receiver including a light receiving element, wherein a current for causing the light emitting element to emit light is controlled at a constant current during transmission. Optical communication control device. 2. An optical communication control device comprising an optical transmitter including a light emitting element and an optical receiver including a light receiving element, wherein an output voltage of the light receiving element is compared with a reference voltage which has been made into a constant voltage. An optical communication control device characterized by reproducing data. 3. An optical communication control device comprising a light transmitting means including a light emitting element and a light receiving means including a light receiving element, wherein a plurality of the light emitting elements are provided, and an arbitrary number of the light emitting elements among the plurality of light emitting elements. An optical communication control device characterized in that it is configured to selectively drive. 4. A configuration in which some of the plurality of light emitting elements are selectively driven when a communication error occurs or when the communication error rate exceeds a predetermined value. Optical communication control device. 5. An optical communication control device comprising an optical transmitting means including a light emitting element and an optical receiving means including a light receiving element, comprising means for changing a light emitting element drive current, and the above means is provided according to the situation of a communication error. An optical communication control device characterized by changing a light emitting element drive current.