JP2894466B2 - Photodetector bias control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bias control circuit for a light receiving element, and more particularly, to a receiving section having a light receiving element for transmitting optical data and requiring a variable bias of a load circuit depending on the intensity of a light receiving signal. ).

[0002]

2. Description of the Related Art With the advancement of information communication transmission technology, light is used as one of transmission means, and a light emitting element is used as a light source from the viewpoint of equipment configuration and peripheral circuits. In particular, it is common practice to add a remote control function to home appliances and AV devices in order to enhance operability in order to enhance operability.

Since the amount of light received is inversely proportional to the square of the distance from the light source, when the light-emitting and light-receiving elements are considered, if the light-emitting side moves within a range of 10 m to 30 cm, the light-source side has the same light source intensity. Even so, the difference changes about 1000 times. Therefore, at this time, in order to obtain the same output from the light receiving element regardless of the movement range on the light emitting side, it is necessary to change the load resistance by 1000 times as signal processing on the control circuit side of the light receiving element.

Using a photodiode 1 as a light receiving element,
After appropriately processing the output of the photodiode 1,
FIG. 3 shows a circuit example in which the microcomputer 7 decodes and forms a reception output. In such a light-receiving element detecting circuit, a conventionally used bias level adjusting circuit detects an output of the preamplifier 2 by an auto bias / level controller 8 and varies an external variable resistor 9 according to the output. A method of controlling a resistance value so as to obtain an appropriate level of output is employed.

[0005]

The above-mentioned conventional system can be expected to have a great effect when the light emitting source is single and the light receiving portion is shielded from other light sources, but there is extraneous optical noise. In this case, if the noise is larger than the signal light, the auto bias / level controller 8 operates in response to the noise light, sets an incorrect bias level to the light receiving element,
As a result, an output corresponding to the original received signal cannot be obtained, resulting in a malfunction.

In general, extraneous light noise is often periodic pulse noise of a fluorescent lamp or the like, while an auto-bias level controller requires a recovery time due to its circuit configuration. ,
All of the data up to the noise pulse and the signal data between the noise pulses become misbiased, and the signal cannot be detected.

By the way, in general, optical digital transmission including the above-mentioned remote control function requires some error correction. Error correction is a well-known technique and will not be described in detail.However, by adding a signal for determining whether the data is correct or a signal for correcting erroneous data to correct data to the signal data to be transmitted, Also, measures are taken to enable the original correct data to be demodulated even if a part of the data is missing or erroneous data is inserted.

[0008] The problem of the noise caused by the setting of the bias level as described above is a problem that occurs at the time of light reception even if the transmission system employs advanced error correction or parity in signal processing. No effect could be expected and demodulation of the original signal data was difficult.

An object of the present invention is to provide a light receiving element bias level which can be set to an optimum bias for original signal data without adjusting the bias level to the external light noise even when the external light noise is input as described above. It is to provide a control circuit.

[0010]

Means for Solving the Problems To achieve the above object,
Because in the present invention includes a microcomputer output of light receiving elements are entered, the microcomputer, an error check unit to perform error checking demodulates the output of the light receiving element, and detects the presence or absence of output of the light receiving element A light receiving detector, and a bias level controller for forming a bias level setting signal from the output of the light receiving detector and the signal of the error checker; In the bias control circuit of the light receiving element connected , the bias level control unit
Can step change the bias level
The bias step is the highest sensitivity
After setting the bias step to
For each step, the error rate in that step
Measure based on the output of the check section and obtain from the measurement result.
The minimum error rate step to the optimal bias point
It is designed to work as follows.

[0011]

When the output of the light receiving element is detected by the light receiving detecting section of the decoding microcomputer, the bias level of the light receiving element is detected by the bias level control section of the microcomputer.
The level is changed in steps, and the error rate in each step is measured for each step. The optimum bias point of the original signal data can be obtained by setting the minimum error rate step obtained from the measurement result as the optimum bias point.

Even if pulsed noise light stronger than the signal light is mixed, the error rate distribution of the pulsed noise is clearly different from that of the signal data, and the microcomputer determines this and sets the bias level. Therefore, the light receiving element is not auto-biased to the noise level, so that the signal data is lost only in the noise part of the pulse, so that the true data can be easily demodulated by performing the error correction processing.

[0013]

FIG. 1 is a block diagram showing an embodiment of the present invention in which a photodiode is used as a light receiving element in a digital bias type remote control device.

An output of the photodiode 1 formed by receiving light emitted from a light emitting element such as an infrared light emitting diode is input to a preamplifier 2, amplified, and given to a limiter amplifier 3. Thereafter, the signal level is adjusted and extracted to a signal level in a preset range by the band-pass filter 4, and the output signal is further pre-processed by a circuit to which a detector / integrator 5 and a hysteresis comparator 6 are connected. The data is input to the decoding unit 11a of the computer 11. The microcomputer 11 performs signal processing such as error check and correction based on a predetermined program on the input signal as performed by a remote control device, decodes the light receiving element output, and outputs the data output. Form.

The microcomputer 11 of this embodiment
Is a control signal Q for adjusting the bias level of the light receiving element 1 in addition to the function of decoding the output of the light receiving element 1.
To form

That is, the output of the preamplifier 2 is input to the microcomputer 11, and a signal is detected by the light reception detection unit 11b. The output of the light reception detection unit 11b is supplied to the bias level controller 11c. An error counter 11d is separately provided in the bias level controller 11c.
Is input. The error counter 11d counts the error signal of the light receiving element output checked by the decoding unit 11a and calculates an error rate.

The bias level controller 11c changes the bias level in steps having a predetermined interval by using the output of the light receiving detector 11b as a trigger, and detects the level of the output of the preamplifier 2 in each step. The bias level controller 8 measures the error rate based on information from the error counter 11d. The distribution of the measured error rate is determined, and a bias level control signal Q is formed.

A digital control signal Q for instructing a bias level formed by the microcomputer 11 is D / D
An A-converter 10 converts the analog signal into an analog signal. The analog signal is supplied to a variable resistor 9 connected to a power supply circuit.

Next, the bias level control operation of the microcomputer 11, particularly the bias level controller 11c, will be described in detail with reference to the flowchart of FIG. The following operation is programmed together with the microcomputer that has programmed the error correction operation in digital transmission.

In the circuit shown in FIG. 1, the bias level of the light receiving element 1 is set by the resistance value of the variable resistor 9. The switching of the bias level is performed stepwise at intervals programmed in advance, and the light receiving element 1 is used. When the photodiode 1 has no input light, the output of the preamplifier 2 is at a “high” level, and when there is input light, it is at a “low” level.

(1) First, at the start of operation, the microcomputer 11 outputs a command to the D / A converter 10 from the bias level controller 11c so that the resistance value of the variable resistor 9 becomes maximum, that is, a maximum sensitivity control signal Q. I do. As a result, the sensitivity of the light receiving element 1 is maximized, and a "low" level output is provided from the preamplifier 2 to the light receiving detection unit 11b of the microcomputer as a detected light receiving output.

(2) Bias level controller 11c
Outputs to the D / A converter 10 a control signal Q for lowering the bias step by one step until the input signal to the light receiving detector 11b changes to the "high" level, and influences external noise as an initial setting. Set the maximum sensitivity bias level that will not be used.

(3) If the input to the light receiving and detecting section 11b of the microcomputer becomes "high" level by the above operation, the microcomputer waits in this state and maintains the bias step until it becomes "low" level. That is, the light receiving element 1 receives the input light at the bias level maintained by the control signal Q,
If the input light is at a predetermined level, a "low" signal is output from the preamplifier 2 to the light reception detection unit 11b as a detection signal.

(4) In the above step, if the input signal of the light receiving detector 11b of the microcomputer becomes "low" level by detecting the input light, it is determined whether or not the detected light is due to regular data. Then, all the bias step points are scanned again, and the error rate of the signal in each step is measured by the error counter 11d based on the signal of the decoding unit 11a.

(5) If the result measured in each step is error-correctable, and if a series of measurement results includes a point having the minimum error rate, it is determined that the point has an appropriate bias level and the point having the minimum error rate is determined. To fix the bias level. The decoding unit 11a decodes a signal of the light receiving element 1 detected at a fixed bias level to form an output.

(6) If error correction is impossible or the existence of the minimum error rate point cannot be found during the scanning operation, the input light is regarded as noise and the process returns to step (1).

(7) In the process of step (5), if the state in which error correction is impossible is continued for, for example, 2 seconds, it is determined that a light receiving failure has occurred due to interruption of input light or movement of the light emitting source. Judgment is made, and the operation is started again from step (1).

Although the above embodiment has been described with reference to a remote control device, the present invention can be applied to bias level control of a light receiving element in another optical transmission system.

[0029]

As described above, in the conventional optical optimum bias setting method, demodulation could not be performed at all when noise light stronger than signal data was input. By effectively utilizing a microcomputer required for error correction in processing, a transmission system resistant to noise can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a digital bias type remote control receiving system according to an embodiment of the present invention.

FIG. 2 is an exemplary flowchart for explaining the operation of the microcomputer according to the embodiment;

FIG. 3 is a block diagram showing a conventional remote control receiving system.

[Explanation of symbols]

 Reference Signs List 1 light receiving element 2 preamplifier 9 variable resistor 10 D / A converter 11 microcomputer 11a decoder 11b light receiving detector 11c bias level controller 11d error counter

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ identification symbol FI H04B 10/18 (58) Investigated field (Int.Cl. ⁶ , DB name) H03G 3/20 H04B 10/02

Claims (1)

(57) [Claims] [Claim 1 further comprising a microcomputer output of light receiving elements are entered, the microcomputer, an error check unit to perform error checking demodulates the output of the light receiving element, and detects the presence or absence of output of the light receiving element A light receiving detector, and a bias level controller for forming a bias level setting signal from the output of the light receiving detector and the signal of the error checker; In the bias control circuit of the connected light receiving element , the bias level control section controls the bias level in a step.
Can be changed and the via
Set the bias step to the most sensitive bias step.
After that, change it sequentially, and
Error rate based on the output of the error check unit
And the step with the smallest error rate obtained from the measurement results
It is especially important to operate to the optimum bias point.
Bias control circuit for light receiving element.