JPH10275939A - Control circuit of emission intensity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust the amount light emission according to a distance between information equipment. SOLUTION: An output current 11 flows to a photodetector 3 according to the amount of received light of the photodetector 3, and the output current 11 is converted to a voltage V1 by a current/voltage conversion circuit 4. The voltage V1 is transmitted to a post-stage circuit via an output terminal OUT. Also, the peak value of the output voltage V1 is detected by a level detection circuit 7. An output signal (a) of the level detection circuit 7 is applied to a drive circuit 9 and a drive capacity is changed. The drive circuit 9 generates an output signal (c) of either 0 or 1 according to input data (b) and the level of the output signal (c) is adjusted, based on the output signal (a). The output signal (c) is amplifier by a transistor 1, and a light-emitting element 2 emits or does not emit light depending on the collector current of the transistor 1. When a peak value is high, the amount of emission becomes low. On the other hand, when the peak value is low, the amount of emission becomes high.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emission intensity control circuit suitable for use in two-way communication means using light as a medium.

[0002]

2. Description of the Related Art In general, there is known a system for performing two-way communication between information devices by using light such as infrared light as a medium. On the data transmitting side of such information equipment, the light transmitting element causes the light emitting element to emit light in accordance with the data "1" or "0", and on the receiving side, the transmitted light is received by the light receiving element. Is converted to data in accordance with the output signal of. In the data transmission side of such a system, FIG.
The light emitting element emits light based on data corresponding to "1" and "0" using the light emitting circuit as described above. FIG. 5 is a circuit diagram showing a conventional light emitting circuit.

In FIG. 5, an input signal corresponding to data "1" or "0" to be transmitted is applied to the base of the transistor 1 via an input terminal IN, and the transistor 1 is turned on or off according to the input signal. . When the transistor 1 is turned on, the collector current of the transistor 1 flows through the light emitting element 2, and the light emitting element 2 emits light. When the transistor 1 is turned off, no current flows through the light emitting element 2, so that
The light emitting element 2 does not emit light. In this way, the light emitting element 2 emits or does not emit light according to “1” or “0”, and transmission of transmission data is performed.

The amount of light emitted from the light emitting element 2, that is, the light emitting power is determined by the magnitude of the current flowing through the light emitting element 2.
The power supply voltage is Vcc, the collector-emitter saturation voltage of the transistor 1 is Vce (sat), and the light emitting element 2
Is the forward voltage of VD and the resistance value of the resistor R is R, the current I flowing through the light emitting element 2 is I = （Vcc− (V
D + Vce (sat)) / R (1) Therefore, the light emission power of the light emitting element 2 can be set according to the resistance value of the resistor 3.

[0005]

Such two-way communication means using light as a medium is also used in portable information equipment. In general, power consumption of portable information devices is problematic due to battery operation, and it is desired to provide portable information devices with low power consumption. However, in the light emitting circuit as shown in FIG. 5, the light emitting element 1 is always made to emit light with a fixed strong power so that transmission can be performed even if the distance between the information devices is long. When the light emission power does not need to be increased, there is a problem that unnecessary current consumption increases.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a light emission intensity control circuit for controlling the intensity of a light emitting element, comprising: a light detection circuit for generating an output signal in accordance with the amount of light received by a light receiving element; A level detection circuit for detecting a level of an output signal of the circuit; and a drive circuit for setting a driving capability by the output signal of the level detection circuit and driving the light emitting element according to data to be transmitted. It is characterized by.

[0007] Further, the present invention is characterized in that when the level of the output signal of the photodetector circuit is high, the driving capability of the driving circuit is reduced, and when the level is low, the driving capability is increased. Further, a level variable circuit is provided between the light detection circuit and the level detection circuit, and a level variable circuit is configured to set a variable amount by an output signal of the level detection circuit.

In the present invention, the level of the output signal is detected from the output signal of the photodetector circuit corresponding to the amount of received light, and the driving capability of the drive circuit is changed according to the detected level. When the detected level is high, the driving capacity is low,
When the detected level is low, the driving capability is high. The driving circuit drives the light emitting element with the driving capability set according to the output signal of the level detection circuit and according to the data to be transmitted.

[0009]

FIG. 1 is a diagram showing an embodiment of the present invention. Reference numeral 3 denotes a receiving element for receiving transmitted light;
Is a current-to-voltage conversion circuit including a differential amplifier circuit 5 in which the receiving element 3 is connected to the negative input terminal, and a resistor 6 connected between the negative input terminal and the output terminal of the differential amplifier circuit 5. A level detection circuit for detecting the peak value of the output voltage of the current / voltage conversion circuit 4, a holding circuit 8 for holding the output signal of the level detection circuit 7, a driving circuit 9 for driving the transistor 1 based on data to be transmitted, and a holding circuit 8 Is a drive circuit that changes the output current supplied to the base of the transistor 1 in accordance with the output signal of the transistor 1. In addition, about the same circuit as the conventional example of FIG.
The same reference numerals as in FIG.

In FIG. 1, of two devices that communicate with each other, data is transmitted from a transmitting device (not shown) to a receiving device using light such as infrared light as a medium, and the data is transmitted to a light receiving element 3. Is received. When the received data is "1", the receiving element 3 is irradiated with light and an output current I1 is generated from the receiving element 3. When the received data is "0", the receiving element 3 is not irradiated with light and the output current I1 is output. No current I1 is generated. The output current I1 is supplied to the current-voltage conversion circuit 4. In the current-voltage conversion circuit 4, since the differential amplifier 5 is in a balanced state, only the feedback signal is supplied to the negative input terminal of the differential amplifier 4. Applied. Therefore, the output current I1 is supplied to the resistor 6 and converted into an output voltage V1 as shown by a solid line in FIG. The output voltage V1 is output from the output terminal OUT.
Is transmitted to a signal processing circuit such as a decoder at the subsequent stage.

The output voltage V1 is applied to a level detection circuit 7, and its peak value is detected. The peak value is a level when light is applied to the light receiving element 3, and the output voltage V1 changes according to the intensity of the received light. That is, when the distance between two devices that communicate with each other is long, the intensity of the received light is weak and the magnitude of the output current I1 is small, so that the output voltage V1 is as shown by the dotted line in FIG. Lower. When the distance is short, the intensity of the received light is strong,
The output voltage V1 increases as shown by the dashed line in FIG.

Thereafter, an output signal a is generated from the level detection circuit 7 in accordance with the peak value, and is held in the holding circuit 8.
The held output signal a is applied to the driving circuit 9, and the driving capability of the driving circuit 9 is changed by the output signal a. That is, the driving capability increases when the peak value is low, and decreases when the peak value is high. On the other hand, the driving circuit 9 has
Input data b indicating "1" and "0" as shown in (b) is applied, and the drive circuit 9 supplies an output signal c based on the input data to the base of the transistor 1. Input data b
Indicates "1", the output signal c is supplied to the base of the transistor 1, and the transistor 1 is turned on. When "0", the output signal c is not generated and the transistor 1 is turned off. When the transistor 1 is turned on and off, the collector current changes as shown in FIG. 2C, and the collector current flows to the light emitting element 2 or stops flowing. Since the light emitting element 2 emits light according to the presence or absence of the collector current, the light emitting element 2 enters a light emitting state or a non-light emitting state according to the input data b.

When the input data b is "1" and the transistor 1 is turned on, the output signal c is amplified by the transistor 1. Output signal a of level detection circuit 7
When the drive capability of the drive circuit 9 changes according to
Changes in size. Therefore, assuming that the gain of the transistor 1 is constant, the collector current of the transistor 1 also changes. That is, as shown in FIG. 2C, when the driving capability of the driving circuit 9 is high, the collector current of the transistor 1 becomes higher than that of FIG.
As shown by the dotted line in FIG. 2C, when the driving capability is low, the collector current decreases as shown by the solid line in FIG.
Therefore, when the driving capability of the driving circuit 9 is high, the light emission intensity of the light emitting element 2 is high, and when the driving capability is low, the light emission intensity is low.

Therefore, the relationship between the distance between the devices communicating with each other and the amount of light emitted from the light emitting element 2 is as shown in FIG. 2 (d). When the distance is long, the intensity of the received light decreases. Since it is weak, the driving capability of the driving circuit 9 is increased, and the intensity of light from the light emitting element 1 is increased. When the distance is short, the received light is strong, so that the driving ability is weakened and the light emission intensity is weakened.

In the IrDA standard, transmission and reception are performed alternately. Therefore, if the output signal of the level detection circuit 7 detected at the time of reception is held, the signal can be transmitted with a driving capability suitable for the intensity of the received light at the time of transmission. Holding circuit 8
May be configured by a circuit well known in the art, and may be held by analog processing using a capacitor or digital processing using a memory.

FIG. 3 is a diagram showing another embodiment.
The difference from FIG. 1 is that a variable gain amplifier circuit 9 is inserted between the current-voltage conversion circuit 4 and the level detection circuit 7,
And a gain control circuit 10 for changing the gain of the variable gain amplifying circuit 9 according to the output signal a of the level detecting circuit 8. In FIG. 3, a difference of the operation from FIG. 1 will be described. The output voltage V1 of the current-voltage conversion circuit 4 is amplified by the variable gain control circuit 10, and the peak value of the output signal d of the variable gain amplification circuit 10 is detected by the level detection circuit 7. The output signal a of the level detection circuit 7 is not only
It is also applied to the gain control circuit 11. Gain control circuit 1
1 compares the output signal a with the reference value Vref, and applies an output signal e corresponding to the difference to the variable gain amplifier circuit 10.
Then, the gain of the variable gain amplifier circuit 10 is changed according to the output signal e. Therefore, when the peak value of the output signal d is lower than the reference voltage Vref, the gain of the variable gain amplifier circuit 10 is increased, and when the peak value is higher than the reference voltage Vref, the gain is reduced. Therefore, the variable gain amplifier circuit 10
Is adjusted so that the peak value of the output signal d becomes equal to the reference voltage Vref. Therefore, the output signal d whose level is stabilized can be transmitted to the subsequent circuit via the output terminal OUT.

In such a configuration, the level detecting circuit for controlling the driving capability of the driving circuit and the level detecting circuit for adjusting the level of the output signal from the output terminal OUT can be constituted by one circuit. 3 can be simplified. In FIGS. 1 and 3, when the configuration is changed so that the output voltage V1 becomes the voltage on the power supply voltage side when the light receiving element 3 is not irradiated with light, the light is irradiated, and the output is performed according to the amount of received light. Since the bottom value of the voltage V1 changes, in this case, the light emission amount of the light emitting element 2 is adjusted by using the level detection circuit 7 as a circuit for detecting the bottom value.

FIG. 4 is a diagram showing a specific example of the drive circuit shown in FIGS. 1 and 3. Reference numeral 11 denotes a level detection circuit 7 as a base.
The transistor 12 to which the output signal a is applied, the transistor 12 is a transistor differentially connected to the transistor 11, and the transistors 13 and 1
4 is a resistor connected between the bases of the transistors 11 and 12, 15 is a constant current source that generates a constant current, 16 is a switch that turns on and off according to input data b, and 17 is a constant current source via a switch 16. 15 is a current mirror circuit that inverts the output current of 15 and supplies it to the emitters of the transistors 11 and 12.

First, input data b of "1" or "0"
, The switch 16 is turned on / off. Switch 1
When the switch 6 is turned on, the output current of the constant current source 15 is supplied to the transistors 11 and 12 via the current mirror circuit 17 and is shunted to the transistors 11 and 12. The collector current of transistor 11 is supplied to transistor 1,
As a result, the collector current of the transistor 1 flows to the light emitting element 2, and the light emitting element 2 emits light. Conversely, when the switch 16 is turned off, the output current of the constant current source 15
7 and is not supplied to transistors 11 and 12. As a result, since no collector current is generated from the transistor 11, the light emitting element 2 does not emit light. In this manner, the light emitting element 2 emits light or emits no light according to the input data.

The output signal a of the level detection circuit 7 is applied to the base of the transistor 11,
A reference voltage Vr is applied to the base of. Transistor 1
Since 1 and 12 are differentially connected, the voltage between the bases of the transistors 11 and 12 changes according to the level of the output signal a, and the distribution from the output current of the current mirror circuit 17 to the transistors 11 and 12 changes. That is, the output signal a
However, when the voltage is higher than the reference voltage Vr, the collector current of the transistor 11 becomes smaller than the collector current of the transistor 12, and when the voltage is lower than the reference voltage Vr, the collector current of the transistor 11 is larger than the collector current of the transistor 12. Thus, as the level of the output signal a increases, the collector current a of the transistor 11 decreases,
Since the collector current of the transistor 1 also decreases, the light emission amount of the light emitting element 2 decreases.

In the circuit of FIG. 3, the magnitude of the current c supplied to the base of the transistor 1 is adjusted using the linear region of the differential circuit including the transistors 11 and 12. By inserting the resistors 13 and 14 as shown in FIG. 3, the linear region can be expanded, and the change in the amount of light emitted from the light emitting element 2 can be adjusted according to the resistors 13 and 14.

[0022]

According to the present invention, when the amount of received light is small,
The drive capacity of the drive circuit increases, the amount of light emission increases,
Also, when the amount of received light is large, the driving ability is reduced and the amount of emitted light is reduced. Therefore, the amount of emitted light changes according to the distance between the information devices. In particular, the amount of emitted light decreases when the distance is short,
Power consumption can be reduced.

Further, since the output signal level of the light detection circuit is adjusted according to the output signal of the level detection circuit, an output signal having a stable level can be obtained. In addition, since the level detection circuit can be used for two purposes, that is, the adjustment of the light emission amount and the stability of the output signal, the circuit configuration can be simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing each output signal of the circuit of FIG.

FIG. 3 is a block diagram showing an embodiment of the present invention.

FIG. 4 is a circuit diagram showing a specific circuit example of the drive circuit 9 of FIGS. 1 and 3;

FIG. 5 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transistor 2 light emitting element 3 light receiving element 4 current / voltage conversion circuit 5 differential amplifier 6 feedback resistor 7 level detection circuit 8 holding circuit 9 drive circuit 10 variable gain amplifier circuit 11 gain control circuit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kanji Tanaka 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (4)

[Claims] 1. A light emission intensity control circuit for controlling the intensity of a light emitting element, comprising: a light detection circuit for generating an output signal in accordance with an amount of light received by a light receiving element; and detecting a level of the output signal of the light detection circuit. A level detecting circuit for controlling the emission intensity, the driving capability being set by an output signal of the level detecting circuit, and a driving circuit for driving the light emitting element according to data to be transmitted. circuit. 2. The emission intensity control circuit according to claim 1, wherein when the level of the output signal of the photodetection circuit is high, the driving capability of the driving circuit is reduced, and when the level is low, the driving capability is increased. 3. A level variable circuit inserted between the light detection circuit and the level detection circuit, wherein a variable amount is set by an output signal of the level detection circuit. Item 2. A light emission intensity control circuit according to Item 1. 4. The light intensity control circuit according to claim 1, further comprising a holding circuit for holding an output signal of the level detection circuit and applying the held signal to a driving circuit.