JPH02118429A - Light quantity deterioration detecting circuit - Google Patents

Abstract

PURPOSE:To decide the deterioration of a light properly by inputting a light output signal detected by a photodetector to a peak value detecting circuit and a mean value detecting circuit and comparing the difference between both extracted values with a preset value. CONSTITUTION:The light output signal emitted by the light source 11 is detected by the photodetector 12 and converted into an electric signal. This light output signal is branched by a branch circuit 13, one is inputted to the peak value detecting circuit 14, and the other is inputted to the mean value detecting circuit 15. The circuit 14 detects the peak value of the light output signal and detects the maximum value in one cycle of the light output signal. The circuit 15, on the other hand, calculates the mean value of the light output signal in one cycle. The outputs of the circuits 14 and 15 are both inputted to a differential circuit 16, which calculates the difference between the peak value and mean value of the light output signal. This difference is inputted to a comparing circuit 17 and compared with the set value set at a voltage setting terminal 18. When the difference is smaller than the set value, deterioration information on the light source 11 is outputted from a deterioration detection output terminal 19.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light source deterioration detection circuit for a light source using an optoelectronic device.

[Conventional technology]

For example, a light source deterioration detection circuit for a light source using an optoelectronic device such as a light emitting diode or a laser diode detects the output level of the light source with a photodetector such as a photodiode, and the average level satisfies a predetermined set value. I was making a judgment based on whether or not it was. In addition, if the light output of the light source is controlled to be constant by an optical output control circuit (APC circuit), the amount of increase in the bias current value of the light source is detected, and this bias current value is set to a predetermined set value. A circuit configuration has been adopted in which the deterioration of the light source is determined based on whether or not the light source is within the range of .

[Problem to be solved by the invention]

However, such conventional light source deterioration detection circuits may not be able to accurately detect light source deterioration depending on how the set values are selected. In particular, if the device has an APC circuit, depending on the setting of the bias current value that determines that the light source has deteriorated, even if the extinction ratio deteriorates and affects the transmission characteristics, it should not be determined that the light source has deteriorated. There is. Conversely, even if the extinction ratio is sufficiently large and there is no problem with transmission characteristics, if the bias current increases, it may be determined that the light source has deteriorated.

[Means to solve the problem]

The present invention provides a peak value detector that detects the peak value of the optical output signal of a light source, an average value detection circuit that calculates the average value of the optical output signal of the light source, and an average value of the peak value of the optical output signal and the average of the optical output signal. The present invention is characterized in that a comparison circuit is provided that determines that the light source has deteriorated when the difference in values is smaller than a predetermined set value.

[Effect]

Since the extinction ratio of the light source is determined based on the difference between the peak value of the light output signal of the light source and the average value of the light output signal of the light source, deterioration of the light source can be accurately determined.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a circuit diagram showing an embodiment of a light source deterioration detection device according to the present invention. A light output signal emitted from a light source 11 is detected by a photodetector 12 and converted into an electrical signal. The optical output signal converted into an electrical signal is branched by a branch circuit 13, and one of the branched optical output signals is sent to a peak value detection circuit 14.
and the other is input to the average value detection circuit 15.

The peak value detection circuit 14 detects the peak value of the optical output signal, and detects the maximum value within one cycle of the optical output signal. On the other hand, the average value detection circuit 16 calculates the average value of one period of the optical output signal. Peak value detection circuit 14
and the output of the average value detection circuit 15 are both output from the differential circuit 16.
The difference between the peak value and the average value of the optical output signal is calculated here. The output of the differential circuit 16, that is, the difference between the peak value and the average value of the optical output signal, is input to a comparator circuit 17 and compared with a set value set at a voltage setting terminal 18. When the difference between the peak value and the average value of the optical output signal is smaller than the set value, deterioration information of the light source 11 is output from the deterioration detection output terminal 19.

FIG. 2 is a characteristic diagram showing the operation of the light source deterioration device of the present invention. FIG. 2(a) shows that the extinction ratio of the light source 11 is small.
The waveform of the optical output signal is shown when the signal is degraded. That is, this shows a case where the difference between the peak value VP and the average value V is small.

On the other hand, FIG. 2(b) shows the optical output signal waveform of the photodetector 12 when the light source 11 has a large extinction ratio and the light source 11 is in a normal state. As can be seen from the figure, the peak value V,
The difference between this and the average value Vi is large.

In the case of FIG. 2(a), since the extinction ratio is small, it affects the transmission characteristics. This has two peak values V and an average value V compared to the case of FIG. 2(b). This is because the ratio between

Here, the light source 11 is not normal as shown in Fig. 2 (b) due to deterioration over time.
) to the state shown in Figure 2(a),
The output of the differential circuit 16 changes at a time point T when the state changes as shown in FIG. 2(C). In other words, Vl changes to V2, and the output v2 of the differential circuit 16 after the change becomes smaller than the set value VTH of the voltage setting terminal 18, so the output of the comparator circuit 17 becomes as shown in FIG. 2(d). Then, the output voltage of the deterioration detection output terminal 19 changes and is output as deterioration information of the light source 11.

〔Effect of the invention〕

As explained above, according to the present invention, the optical output signal detected by the photodetector is manually input to the peak value detection circuit and the average value detection circuit, and the respective outputs are input to the differential circuit, and the difference between the two is calculated. Since the light source is taken out, inputted into a comparison circuit, and compared with a set value set appropriately in advance, it is possible to appropriately determine the deterioration of a light source whose extinction ratio has deteriorated.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, and FIG. 2 is a characteristic diagram showing the operating characteristics of one embodiment of the present invention. 11...Light source, 12...Photodetector, 1
3... Branch circuit, 14... Peak value detection circuit, 15... Average value detection circuit, 16...
...Differential circuit, 17...Comparison circuit, 18...
...Voltage setting terminal, 19... Deterioration detection output terminal. Leap figure 2

Claims (1)

[Scope of Claims] A photodetector that detects the optical output of a light source using an optoelectronic device; a peak value detector that detects the peak value of an optical output signal obtained by the photodetector; and the photodetector. an average value detection circuit that calculates the average value of the optical output signal obtained by the device; a differential circuit that calculates the difference between the peak value of the optical output signal and the average value of the optical output signal; and this differential circuit. A light source deterioration detection circuit comprising: a comparison circuit that determines that the light source has deteriorated when the difference obtained is smaller than a predetermined set value.