JPH02159135A - Transmitting device for optical radio data - Google Patents

Abstract

PURPOSE:To use a light emitting element with higher efficiency by driving intermittently the light emitting element and thereby to suppress the temperature rise of the element. CONSTITUTION:A light emitting element is turned on and off at a prescribed time interval. The input dat is written into a buffer 1 with no delay with a write clock and then read of the data out of the buffer 1 is executed with the read clock given from a CPU 2. Thus the output data sent to the CPU 2 from the buffer 1 is sent to a light emitting driver 3. The driver 3 drives a light emitting element 4 based on the received output data and transmits an optical signal. The input data, even if received continuously, are sent from the buffer 1 after the CPU pause time t2 as long as the buffer 1 has a sufficient capacity. Thus it is possible to prevent the inadvertent rise of temperature of a light emitter and to ensure a highly efficient light emitting action.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an optical wireless data transmission device.

(Prior Art) In optical wireless data transmission, a driving current having a waveform as shown in FIG. 8 is applied to a light emitting element (for example, an LED). The figure shows an example of an IMHz (7) PSK data string. Generally, in data transmission, a data string is continuously transmitted in blocks of a certain length, so-called packet units, for a certain period of time 11 (seconds), as shown in FIG. This transmission is performed by converting the driving current into light in a light emitting element and emitting it into space. The magnitude of the drive current applied to the light emitting element is determined based on the lifespan of the element, luminous efficiency, heat dissipation, maximum rating, etc., or is determined by providing a considerable margin for the maximum rating to ensure sufficient safety. I have no choice but to make settings. For this reason, a decrease in efficiency is unavoidable.

A light emitting element generates heat when converting current into light.

The power conversion efficiency of light-emitting elements is only a few dozen percent at most, and most of the drive current is converted into heat. Consider a case where an LED is used as a light emitting element and is driven with a current shown in FIG. 10A. Figure 10A shows 1 packet (data 1)
energize for 1 second, stop for 0.3 seconds, energize for 1 second as 1 packet (data 2), stop for 0.6 seconds,
The case where electricity is applied for 1 second as 1 packet (data 3) is shown.

In this case, the magnitude of the drive current is set to a constant value.

When current is passed through the LED in this manner, the temperature of the light emitter, so-called chip, rises as shown in FIG. 10. That is, by applying electricity from time 10 to time 11, the light emitting device (L
ED) temperature rises from 10°C to T°C. Time 11
to time t2! The temperature in the first floor of the body drops to 12 degrees Celsius, but does not drop to the original 10 degrees Celsius. As this is repeated, the temperature of the LED gradually increases. Semiconductor light emitting devices (LEDs) generally decrease in luminous efficiency as the temperature rises. Therefore, even if the magnitude of the drive current is constant, the light emitting output that can be generated is LE
As the temperature of D increases, the temperature decreases as shown in FIG. 1C.

Even if the current of the same value is passed, the time t. At time t5, the optical output Po was obtained, but at time t5, only the optical output P5 is obtained.

When performing optical wireless transmission, as shown in FIG. 9, the interval between packets (pause time) 1. ■.

[, even if 2 is zero, that is, continuous data is ejected,
Operating conditions must be set so that the temperature of the light emitting element does not rise excessively, and sufficient light output can be obtained even at the maximum temperature. In Figure 10, if the optical output P5 is the minimum required optical output, then the operating temperature T5℃
is the maximum allowable temperature. Assuming such a case,
An output greater than the optical output P5 can be considered as an excess portion, and producing such an excess output reduces the efficiency of the entire light emitter.

(Problem to be solved by the invention) As described above, in the conventional optical wireless data transmission device,
As light is emitted from the light emitting element, its temperature rises and its luminous efficiency inevitably decreases, and in anticipation of this, a large current may be initially passed to obtain a larger light output than necessary. Therefore, it cannot necessarily be said that the light emitting element is operated with high efficiency.

The present invention has been made in view of the above, and its purpose is to:
An object of the present invention is to provide an optical wireless data transmission device that can convert electricity into light and emit it with high efficiency while preventing a rise in temperature of a light emitting element.

(Means for Solving the Problems) A first optical wireless data transmission device of the present invention applies a drive current modulated in a modulator according to data to be transmitted to a light emitting element, and transmits the data from the light emitting element. An optical wireless data transmission device that outputs the data as an optical signal includes a buffer that sequentially stores the data each time the data is input, and a buffer that reads the data from the buffer in the order in which it was input and provides it to the modulator. The control means is configured to include a control f1 stage that repeats reading for the predetermined read time and reading pause for a predetermined pause time when the read exceeds a predetermined read time. .

In the second optical wireless data transmission device of the present invention, a drive current modulated in a modulator according to data to be transmitted is applied to a light emitting element, and the data is emitted from the light emitting element as light No. 1a. An optical wireless data transmission device, comprising: a buffer that sequentially stores the data each time the data is input; a temperature detection means that detects the temperature from a physical quantity corresponding to the temperature of the light emitting element; input from the buffer to the data; a control means for reading out the stored data in the input order and applying it to the modulator, and stopping the reading when the temperature detected by the temperature detection means exceeds a predetermined first temperature; and a control means for restarting the reading when the detected temperature of the detection means drops below a predetermined second temperature due to the suspension.

(Function) In the first and second optical wireless data transfer devices of the present invention, input data is sequentially stored in a buffer. The input data is read out intermittently by the control means in order to prevent the temperature of the light emitting element from rising too much.

That is, in the first device, when the readout time becomes long, the readout is performed intermittently by repeating a predetermined readout time and a predetermined pause time. In addition, the second device monitors the temperature of the light emitting element, and stops reading when the temperature becomes higher than a predetermined first temperature, and stops reading when the temperature becomes lower than a predetermined second temperature. resume. The data thus read out is applied to a modulator in both the first and second devices, where it modulates the drive current. The modulated drive current drives the light emitting element intermittently and is emitted as an optical signal while suppressing the temperature rise of the light emitting element.

(Example) Before explaining the present invention in detail, the principle of the present invention will be explained in a second example.
This will be explained with reference to the figures.

Assume that the light emitting device (LED) has the following characteristics. That is, as shown in FIG. 2B, when electricity is applied for a time t, the temperature rises to 11°C, and when the body 1 is turned on for a time t, it returns to the original temperature T. The LED returns to ℃. When performing optical wireless data transmission using this LED, if the input data interval (pause time) is less than 2 hours, the conventional situation,
That is, the in degree of the LED gradually increases. Therefore, the driving conditions may be devised so that the time +l- is longer than t2. That is, as shown in FIG. 1A, even if data 1 to 3 are input at intervals shorter than the time t2, the data 1 to 3 are inputted at the same intervals without energizing the light emitting device. As shown in B, the light is supplied to the light emitting device at intervals (rest time) of the time t2 or longer. If you do this, as you can see from C in the same figure,
The temperature of the light emitter rises from T'C to 11 degrees Celsius while the power is on, and from T'C to the original T during rest. ℃ and repeat this process, the temperature of the light emitter never rises above 11℃. As can be seen from the figure, as the temperature of the light emitter increases, the optical output also decreases from P2 to P, but does not decrease below P1. This allows current to be converted into light and transmitted with high efficiency.

FIG. 1 shows an embodiment of the present invention constructed based on the above principle, and FIG. 3 is a timing chart showing its operation. In this embodiment, the light emitting element is turned on and off at predetermined time intervals.

As shown in FIG. 1, input data (FIG. 3B) is transferred to a buffer (e.g., FI) by a write clock (FIG. 3A).
FO) 1 without delay.

Data is read from the buffer 1 using a read clock from the CPU 2 (FIG. 3C). In this way, the output data sent from buffer 1 to CPU 2 (Fig. 3D) is further transmitted to the light emitting driver (modulation 'IA').
) Sent to 3. Based on this output data, the driver 3 drives the light emitting element 4 to emit the optical signal shown in FIG. 3E.

Even if input data is sent continuously, if the buffer capacity is sufficient, the data will be sent from the buffer to the CPU (light emitter) after a pause time t2, and the light emitter will inadvertently rise by 72i degrees. can be prevented, and highly efficient light emitting operation can be performed.

Writing to the buffer is controlled by monitoring the full flag. On the other hand, transmission is performed by monitoring the empty flag until the buffer becomes empty.

FIG. 11 is a flowchart showing an example of the operation of the CPU 2. That is, it is checked whether the data in buffer 1 is H (Sl). If there is, the read clock C is sent out (S2) and data is read. After this, it is checked whether buffer 1 is empty (S3). If it is empty, the read clock C is stopped (S4) and the process returns to Sl. If it is not empty, it is determined whether the energization time has elapsed. If the time has not elapsed, the process returns to S2. If the time has elapsed, the read clock C is stopped (S6).

After this, check whether the pause time has elapsed (S7),
After the pause time has elapsed, the process returns to S2 and reading is resumed.

FIG. 4 is a detailed diagram showing the magnitude relationship between the energization time t and the rest time t2. As you can see from this Figure 4, 1.
<12. That is, the rest time t2 is shorter than the energization time t.
It is necessary to take a long time.

■ This is due to the structure of the LED. The structure of an LED is generally as shown in FIG. That is, a light emitting chip 42 is provided on the -h lead wire 41, and the chip 42 is connected to the other lead wire 44 by a wire 43. And among them, lead wire 41
．． The portion of lens 44 excluding the end portion is molded with a plastic lens 45. Although heat is generated in the chip 42 by energization, the heat is difficult to dissipate. In other words, LEDs have poor heat dissipation. Therefore, the rest time t2 is shorter than the energization time 11.
It is necessary to make it longer.

For a certain LED, how long the energization time t1 and the rest time t2 should be depends on various factors such as the heat dissipation properties of the device itself and the mounting condition, so it is necessary to conduct experiments.

However, the above time 11° [2] changes depending on the ambient temperature, mounting condition, installation method, etc. Therefore, in order to satisfy even the worst case, those times 1. ．．
It is necessary to set 12. For example, if a light emitter is installed on the ceiling, it will be affected by the air flowing out of the air conditioner's vents. For example, the temperature of the light emitter is 70℃ during winter heating.
The temperature ranges from 80°C to 10°C during summer cooling, and the environmental temperature changes significantly.

What's more, even when the air conditioner is turned on or off, the air flow becomes distorted and is affected. Therefore, during the pause time t2, the temperature of the LED is T even under the worst conditions. You have to take it longer to get back to ℃.

Next, a second embodiment of the present invention will be described.

In this second embodiment, on/off control is performed depending on the actual temperature of the light emitting element. That is, energized, off +l-
The repeated control can also be performed based on the temperature of the LED. That is, the LED is allowed to emit light freely until the temperature reaches T1, and when the temperature reaches T1, it is turned on and off, and as the temperature rises, the temperature rises to T. It can be controlled so that it will emit light again when the To carry out such control, as shown in FIG. 2, a light emitting element T-temperature detection means 5 is provided to detect the temperature of the light emitting element 4, and the detected temperature is transmitted to the CPU 2, and the reading clock C is All you have to do is control the output state.

To perform temperature-based control as described above, in order to know the temperature of the LED, some kind of temperature-1 constant element is connected to the LED.
It is conceivable to place it adjacent to.

However, this is difficult to implement due to costs and installation methods. Therefore, it is conceivable to measure the temperature of the LED indirectly using the forward voltage of the LED or the emission intensity.

First, a case using forward voltage will be explained.

The forward voltage VF of a semiconductor light emitting element such as an LED has negative temperature characteristics, as shown in FIG. Therefore, the VF at the operating limit temperature at the operating current value is measured in advance, and the energization is interrupted when the VF during energization reaches -VF. In addition, the forward voltage VFI of the cord was measured and recorded at the start of light emission as shown in FIG.
Further, the forward voltage VF2 during the non-energized time is 11-1 in total. If the light emission is restarted when VF2≧VFI, the rest time of the light emitting element can be controlled based on the temperature.

To measure the forward voltages vF1 and VF2, it is necessary to flow a current that is significantly smaller than the actual operating conditions during the non-energized time, specifically a current of several hundred μA, or to measure it using a current that is much smaller than the actual operating conditions, or to measure the current at a value that is significantly smaller than the actual operating conditions. For example, when the driving pulse width is significantly short, for example, 50 nS, it is possible to conduct measurement by applying a current having the same value as the actual driving time with a pulse width of several nS.

Next, monitor the emission intensity from the LED and
Let us describe the case of knowing the temperature of Light output P of a semiconductor light emitting element such as an LED. has negative temperature characteristics, as shown in FIG. Therefore, measure P at the operating limit temperature at the operating current value in advance, and calculate the optical output P while the current is being applied. is P. The power supply is interrupted when it reaches l. or,
Optical output P at the start of the destination in FIG. is measured and recorded, and furthermore, the optical output P2 is totaled A11j during the non-energized time. Then, if the light emission is restarted when P02≧Po1,
Pause time can be controlled based on the temperature of the light emitting element.

Light output P. 1. To measure Po2, as in the case of measuring the forward voltage described above, a current of a value significantly smaller than the actual operating conditions, specifically a current of several hundred μA, is applied during the non-energized time. Alternatively, for a drive pulse width that is significantly shorter than the actual drive time, for example, 50 nS, a current of the same value as the actual drive time may be applied with a pulse width of several nanoseconds.

FIG. 12 is a flowchart showing an example of the operation of the CPU 2 (FIG. 1) when turning on and off electricity to a light emitting element based on the temperature of the element as described above. That is, check whether there is data in buffer 1 (Sll), and
If so, the read clock C is sent and read is performed. Next, it is checked whether buffer 1 is empty (S13).

If it is empty, the read clock C is stopped and the process returns to Sll.

If it is not empty, it is determined whether the temperature of the light emitting element 4 (FIG. 1) is higher than the set temperature (S15).

If it is not high, the process returns to S14 to continue reading. If it is high, stop the read clock C (S
16). Thereafter, it is determined whether the temperature of the light emitting element 4 is lower than the reading restart temperature (S17). S1 if low
Return to step 2 and resume reading.

(Effects of the Invention) According to the first and second devices of the present invention, since the light emitting element is driven intermittently, the temperature rise of the light emitting element is suppressed and the light emitting element can be used with higher efficiency. be able to.

Furthermore, according to the second device of the present invention, the temperature of the light emitting element is monitored and the light emitting element is turned on and off according to the temperature, so that the light emitting element can be operated more effectively in accordance with the actual situation without waste. Can be driven.

is a timing chart showing the timing, Fig. 4 is a timing chart showing the heat generation and heat dissipation characteristics of the LED, Fig. 5 is a cross-sectional diagram of the LED, and Fig. 6 shows the relationship between the temperature of the light emitting element and the forward voltage. 7 is a diagram showing the relationship between the temperature of the light emitting element and the optical output, FIG. 8 is a waveform diagram showing an example of an optical data string, and FIG. 9 is a timing chart showing the transmission timing of the data string. FIG. 10 is a timing chart showing the temperature and light output of the light emitting element during transmission of the data string in FIG. 9, and FIGS. 11 and 12 show the operation of the CPU of the first and second embodiments of the present invention. It is a flowchart.

1...Buffer, 2...CPU (control means), 3
...Modulator (light emission driver), 4...Light emitting element, 5
...Temperature detection means.

[Brief explanation of the drawing]

Claims (1)

[Claims] 1. An optical wireless data transmission device in which a drive current modulated in a modulator according to data to be transmitted is applied to a light emitting element, and the data is emitted from the light emitting element as an optical signal. , a buffer for sequentially storing the data each time the data is input; and a control means for reading the data from the buffer in the order in which it was input and applying it to the modulator, wherein the reading is performed for a predetermined reading time. an optical wireless data transmission apparatus, comprising: a control means for repeating reading for the predetermined readout time and reading suspension for the predetermined pause time when the time exceeds the predetermined readout time. 2. In an optical wireless data transmission device in which a drive current modulated in a modulator according to data to be transmitted is applied to a light emitting element, and the data is emitted from the light emitting element as an optical signal, the data is inputted. a buffer for sequentially storing the data each time the light emitting element is input; a temperature detecting means for detecting the temperature from a physical quantity corresponding to the temperature of the light emitting element; control means for controlling the modulator, which suspends the reading when the temperature detected by the temperature detection means exceeds a predetermined first temperature; and control means for restarting the reading when the temperature drops below a second temperature.