JPH11308056A - Instrument and method for measuring light quantity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent excessive current from flowing to a photodiode due to incidence of excessive light quantity in a light quantity measuring instrument, wherein the output of an operational amplifier for an output of the photodiode is fed back. SOLUTION: An operational amplifier 23 amplifies current generated by a photodiode 22 in accordance with the incidence of light and outputs it, and the output current is fed back via a feedback resistor 24. Since a current to the photodiode 22 is limited to a value preset by a diode protection circuit 25 although the feedback current is also energized to the photodiode 22, an excessive current is not allowed to flow, even if excessive light is made incident on the photodiode 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a light quantity measuring device such as an optical spectrum analyzer for measuring a light quantity of a light beam and a method thereof.

[0002]

2. Description of the Related Art Hitherto, a light quantity measuring device such as an optical spectrum analyzer has been used for measuring the light quantity of a light beam, and there is, for example, a transimpedance type light quantity measuring device. A first conventional example of such a light quantity measuring device will be described below with reference to FIG. FIG. 1 is a circuit diagram showing a main part of a first conventional light quantity measuring device.

[0003] Here, a light quantity measuring device 1 exemplified as a first conventional example includes a photodiode 2. The photodiode 2 has an output terminal grounded and an input terminal connected to the negative input of an operational amplifier 3. Connected to terminal. The positive input terminal of the operational amplifier 3 is also grounded, and its output terminal is feedback connected to the negative input terminal via a feedback resistor 4.

In the light quantity measuring device 1 having the above structure,
When a light beam to be measured is incident on the photodiode 2, a current corresponding to the amount of light incident on the photodiode 2 is generated. Since this current is amplified and output by the operational amplifier 3, the output allows the light quantity of the light beam to be measured.

Although the current generated by the photodiode 2 as described above is substantially directly proportional to the amount of light, some photodiodes have a characteristic that the generated current is saturated with a large amount of light. In the case of such a light quantity measuring device using a photodiode, it is general to improve a saturation characteristic by applying a bias voltage having a polarity opposite to a generated current to the photodiode.

[0006] Such a light quantity measuring apparatus will be described below as a second conventional example with reference to FIG. However, in the second conventional example, the same portions as those in the first conventional example described above are denoted by the same names and reference numerals, and detailed description is omitted. FIG. 1 is a circuit diagram showing a main part of a light quantity measuring device according to a second conventional example.

Here, a light quantity measuring device 11 exemplified as a second conventional example includes a photodiode 12 having a saturation characteristic, and an input terminal of the photodiode 12 is also connected to the light intensity measuring device of the first conventional example. Like the device 1, it is connected to the operational amplifier 3 and the feedback resistor 4. However, unlike the light amount measuring device 1 of the first conventional example described above, the output terminal of the photodiode 12 is connected to the resistance element 13.
Is connected to a bias power supply 14, and the bias power supply 14 is grounded.

In the light quantity measuring device 11 having the above-described structure, a bias voltage having a polarity opposite to that of the generated current is applied to the photodiode 12 from the bias power supply 14.
It is possible to improve the saturation characteristics of the photodiode 12 that generates a current corresponding to the amount of light.

[0009]

In the light quantity measuring devices 1 and 11 described above, the photodiodes 2 and 12 generate a current in accordance with the light quantity of the incident light, and the light quantity of the light is measured from the current. can do.

However, in the first conventional light quantity measuring device 1, the output terminal of the operational amplifier 3 and the input terminal to which the photodiode 2 is connected are connected via the feedback resistor 4, and the photodiode 2 is connected to the output terminal. Since the generated current is substantially directly proportional to the light amount, the current flows through the photodiode 2 to the output limit of the operational amplifier 3 when the light amount is excessive.

For this reason, when the light amount is excessive, a current larger than the allowable rated current may flow through the photodiode 2, and the photodiode 2 may be destroyed.

In this respect, the second conventional light quantity measuring device 11
In this case, when the current generated by the photodiode 12 increases, the voltage generated in the resistance element 13 also increases, so that the bias voltage decreases and the saturation characteristic of the photodiode 12 works well. In this case, the current flowing through the photodiode 12 is impaired due to the saturation characteristic, so that the flow of an excessive current through the photodiode 12 is suppressed.

However, in the light amount measuring device 11 of the second conventional example, as described above, when the light amount increases, the bias voltage decreases and the suppressed saturation characteristic of the photodiode 12 occurs. The linearity also deteriorates, and the measurement accuracy of the light amount decreases as the light amount increases.

The present invention has been made in view of the above-described problems, and provides a light amount measuring apparatus and method capable of preventing the destruction of a photodiode and maintaining the measurement accuracy even when the light amount increases. The purpose is to:

[0015]

According to a first aspect of the present invention, there is provided a light quantity measuring apparatus, comprising: a photodiode for generating a current in response to the incidence of a light beam to be measured; and amplifying and outputting the current generated by the photodiode. An operational amplifier, a feedback resistor for connecting an output terminal of the operational amplifier to an input terminal to which the photodiode is connected via a predetermined electric resistance, and a preset limit on a current supplied to the photodiode. A diode protection circuit for limiting the current to less than the current.

Therefore, in the light quantity measuring device of the present invention, when the photodiode generates a current in response to the incidence of the light beam to be measured, the operational amplifier amplifies and outputs the current, and the output current is transmitted via the feedback resistor. The feedback is made to the input terminal of the operational amplifier to which the photodiode is connected. The current that is fed back also flows through the photodiode, but the current that flows through the photodiode is limited by a diode protection circuit to a current lower than a current limit set in advance. For this reason, if the current limit is set in accordance with the rated current allowed by the photodiode, even if the photodiode generates an excessive current due to the incidence of excessive light rays, the excess current will exceed the rated current. Is not energized.

According to a second aspect of the present invention, there is provided the light quantity measuring device according to the first aspect, further comprising a bias power supply for applying a bias voltage having a polarity opposite to a generated current to the photodiode, When the current flowing through the diode reaches the limit current, the diode protection circuit limits the bias voltage applied to the photodiode from the bias power supply.

Therefore, since the bias power supply applies a bias voltage having a polarity opposite to that of the generated current to the photodiode, the saturation characteristic of the photodiode is reduced and the linearity of the measurement is improved. When the current flowing through the photodiode reaches the limit current, the bias voltage applied to the photodiode from the bias power supply is limited by the diode protection circuit. Therefore, no bias voltage is applied to the photodiode whose current has reached the limit current.

The third aspect of the present invention is the first or second aspect.
The light quantity measurement device according to claim 1, wherein the diode protection circuit includes a constant voltage circuit that limits a current supplied to the photodiode. Therefore, the current supplied to the photodiode by the constant voltage circuit as the diode protection circuit is limited.

According to a fourth aspect of the present invention, in the light quantity measuring apparatus according to the first aspect, the diode protection circuit includes a second operational amplifier for maintaining the output voltage of the photodiode constant, and a second operational amplifier for the second operational amplifier. A first transistor for supplying a current corresponding to an output voltage to the photodiode, a current detection resistor for detecting a current supplied to the first transistor and the photodiode, and a detection current of the current detection resistor being a limiting current. And a second transistor for limiting a current supplied to the photodiode when the first transistor is reached.

Therefore, the output voltage of the photodiode is kept constant by the second operational amplifier, and a current corresponding to the output voltage of the second operational amplifier is supplied to the photodiode by the first transistor. The current flowing through the first transistor and the photodiode is detected by the current detection resistor, and when the detection current of the current detection resistor reaches the limit current, the current flowing through the first transistor and the photodiode is reduced by the second transistor. Therefore, the current flowing through the photodiode is maintained below the limit current by the diode protection circuit.

According to a fifth aspect of the present invention, in the light quantity measuring device according to the second aspect, the diode protection circuit maintains the output voltage of the photodiode equal to the bias voltage of the bias power supply. A first transistor for supplying a current corresponding to an output voltage of the second operational amplifier to the photodiode; a current detection resistor for detecting a current supplied to the first transistor and the photodiode; And a second transistor for limiting a current flowing through the first transistor and the photodiode when a resistance detection current reaches a limit current.

Accordingly, the output voltage of the photodiode is maintained equal to the bias voltage of the bias power supply by the second operational amplifier, and a current corresponding to the output voltage of the second operational amplifier is supplied to the photodiode by the first transistor. The current flowing through the first transistor and the photodiode is detected by the current detection resistor, and when the detection current of the current detection resistor reaches the limit current, the current flowing through the first transistor and the photodiode is reduced by the second transistor. Is limited by For this reason, the conduction current of the photodiode is maintained below the limit current by the diode protection circuit, and no bias voltage is applied to the photodiode when the conduction current reaches the limit current.

According to a sixth aspect of the present invention, in the light quantity measuring method, a current is generated in the photodiode in response to the incidence of the light beam to be measured, and the current generated by the photodiode is amplified by an operational amplifier and output. A light amount measuring method for feeding back a current to be supplied to an input terminal of the operational amplifier to which the photodiode is connected via a predetermined electric resistance, wherein a current supplied to the photodiode is set to a preset current. It was restricted to the following.

Therefore, according to the light quantity measuring method of the present invention, the current supplied to the photodiode is limited to a value less than the preset limit current. If you set it,
Even if the photodiode generates an excessive current due to the incidence of an excessive light beam, a current exceeding the rated current does not flow through the photodiode.

According to a seventh aspect of the present invention, in the light quantity measuring apparatus according to the sixth aspect, a bias voltage having a polarity opposite to a generated current is applied to the photodiode, and a current flowing through the photodiode is reduced. When the limit current is reached, the bias voltage applied to the photodiode is limited. Therefore, the bias voltage reduces the saturation characteristics of the photodiode, improving the linearity of the measurement.
The bias voltage is not applied to the photodiode whose energizing current has reached the limit current.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. However, the same portions as those in the conventional example described above with reference to the present embodiment are denoted by the same names, and detailed description is omitted. FIG. 1 is a circuit diagram showing a main part of the light quantity measuring device according to the present embodiment, and FIG. 2 is a characteristic diagram showing a relationship between a light quantity incident on a photodiode and an output current.

As shown in FIG. 1, the light quantity measuring device 21 of the present embodiment also includes a photodiode 22 having a saturation characteristic, like the light quantity measuring device 11 of the second conventional example. The photodiode 22 has an input terminal connected to the negative input terminal of the first operational amplifier 23.

The positive input terminal of the first operational amplifier 23 is also grounded, and its output terminal is feedback-connected to the negative input terminal via a resistance element 24. However, unlike the light amount measuring device 11 of the second conventional example described above, the output terminal of the photodiode 22 is connected to a bias power supply 26 via a constant voltage circuit 25 which is a diode protection circuit. The bias power supply 26 is grounded.

In the constant voltage circuit 25, the power supply 2 having a voltage of + V
7 is connected to the output terminal of the photodiode 22 via the first transistor 28 and the current detection resistor 29,
The output terminal of the photodiode 22 is connected to the negative input terminal of the second operational amplifier 30.

A bias power supply 26 is connected to the positive input terminal of the second operational amplifier 30. The output terminal of the second operational amplifier 30 is connected to the gate electrode of the first transistor 28 and the second transistor 32 source electrodes. This second transistor 32
Is connected to the output terminal of the photodiode 22, and the gate electrode is connected to the drain electrode of the first transistor.

The second operational amplifier 30 maintains the output voltage of the photodiode 22 equal to the bias voltage of the bias power supply 26, and the first transistor 28 outputs a current corresponding to the output voltage of the second operational amplifier 30 to the photodiode 22.
And the current detection resistor 29 is connected to the first transistor 2
8 and the photodiode 22 are converted into a voltage and applied to the gate electrode of the second transistor 32.

When the voltage generated by the current detection resistor 29 reaches the limit voltage, the second transistor 32 shifts from the off state to the on state, and switches the resistance element 31 to the second operational amplifier 30.
The current flowing through the first transistor 28 and the photodiode 22 is limited to less than the limited current by short-circuiting the input terminal on the negative side of.

In the configuration described above, the light amount measuring device 21 of the present embodiment also generates a current corresponding to the amount of light incident on the photodiode 22 when the light beam to be measured is incident on the photodiode 22. Since this current is amplified and output by the first operational amplifier 23, the output allows the light quantity of the light beam to be measured.

In the light quantity measuring device 21 of the present embodiment, the photodiode 22 has a saturation characteristic, but a bias voltage having a polarity opposite to the generated current is applied to the photodiode 22 from the bias power supply 26. The saturation characteristic of the photodiode 22 that generates a current corresponding to the amount of light is improved.

Then, the light quantity measuring device 21 of the present embodiment
Then, when the rated current allowed for the photodiode 22 is converted into a voltage by the current detection resistor 29, the voltage causes the second transistor 32 to transition from the off state to the on state. The corresponding limited current is set in the constant voltage power supply 25, and the constant voltage power supply 25 maintains the current supplied to the photodiode 22 below the limited current.

More specifically, the output voltage of the photodiode 22 is maintained at the same level as the bias voltage of the bias power supply 26 by the second operational amplifier 30, and this second operational amplifier 3
A current corresponding to an output voltage of 0 is supplied to the photodiode 22 by the first transistor 28.

The current flowing through the first transistor 28 and the photodiode 22 is detected by a current detecting resistor 29. When the current detected by the current detecting resistor 29 reaches the limit current, the first transistor 28 and the photodiode 22 Is limited by the second transistor 32.

For this reason, the light quantity measuring device 2 of the present embodiment
In 1, the current flowing through the photodiode 22 is maintained below the limit current. Therefore, as shown in FIG. 2, even if an excessive amount of light is incident, a current exceeding the rated current flows through the photodiode 22. And the destruction of the photodiode 22 is prevented.

In addition, when the current supplied to the photodiode 22 reaches the rated current, the application of the bias voltage is also limited, so that the destruction of the photodiode 22 is further effectively prevented. Since the bias voltage is applied to the photodiode 22 until the supplied current reaches the rated current, the linearity of the characteristics of the photodiode 22 is improved satisfactorily in the state where the light quantity is measured.

The present invention is not limited to the above-described embodiment, but allows various modifications without departing from the gist of the present invention. For example, in the above-described embodiment, an example has been described in which the bias voltage is applied from the bias power supply 26 to the photodiode 22 having the saturation characteristic to improve the characteristic.

It is also possible to omit the bias power supply 26 and not apply a bias voltage to the photodiode 22. In this case, as shown in FIG. 2, the linearity of the characteristics of the photodiode 22 is deteriorated, but the constant voltage power supply 25 is still used as a diode protection circuit for maintaining the current flowing through the photodiode 22 below the current limit. Will work.

In the above embodiment, the photodiode 22
Although the first operational amplifier 23 is connected to the input terminal of and the detection result of the light amount is output as a negative current, the output terminal of the photodiode 22 is connected to the output terminal of the photodiode 22 as in the light amount measuring device 41 shown in FIG. It is also possible to connect a single operational amplifier 23 and output the light amount detection result as a positive current.

[0044]

Since the present invention is configured as described above, it has the following effects.

According to the first aspect of the present invention, there is provided a light quantity measuring device, comprising: a photodiode for generating a current in response to an incident light beam to be measured; an operational amplifier for amplifying and outputting a current generated by the photodiode; And a feedback resistor for connecting the output terminal of the photodiode and the input terminal to which the photodiode is connected via a predetermined electric resistance, and restricting a current supplied to the photodiode to a current lower than a preset current limit. A diode protection circuit,
By providing a limit current corresponding to the rated current allowed by the photodiode, a current larger than the rated current does not flow through the photodiode even if an excessive light beam enters, Destruction of the photodiode can be prevented.

According to a second aspect of the present invention, there is provided the light quantity measuring apparatus according to the first aspect, further comprising a bias power supply for applying a bias voltage having a polarity opposite to a generated current to the photodiode. Since the diode protection circuit limits the bias voltage applied from the bias power source to the photodiode when the current flowing through the diode reaches the limit current, the linearity of the characteristics of the photodiode can be improved by the bias voltage. Even when the diode has a saturation characteristic, a large amount of light can be measured satisfactorily, and no bias voltage is applied to the photodiode in which the supplied current has reached the limit current, so that the destruction of the photodiode can be reliably prevented.

The third aspect of the present invention is the first or second aspect.
The light quantity measurement device according to claim 1, wherein the diode protection circuit includes a constant voltage circuit that limits a current supplied to the photodiode, so that a current supplied to the photodiode by the constant voltage circuit serving as the diode protection circuit is reduced. Limited.

According to a fourth aspect of the present invention, in the light amount measuring apparatus according to the first aspect, the diode protection circuit includes a second operational amplifier for maintaining the output voltage of the photodiode constant, and a second operational amplifier for the second operational amplifier. A first transistor for supplying a current corresponding to an output voltage to the photodiode, a current detection resistor for detecting a current supplied to the first transistor and the photodiode, and a detection current of the current detection resistor being a limiting current. By reaching the first transistor and the second transistor that limits the current flowing through the photodiode,
With a diode protection circuit having a simple structure, the current flowing through the photodiode can be reliably limited to a value lower than the current limit.

According to a fifth aspect of the present invention, in the light quantity measuring apparatus according to the second aspect, the diode protection circuit maintains the output voltage of the photodiode equal to the bias voltage of the bias power supply. A first transistor for supplying a current corresponding to an output voltage of the second operational amplifier to the photodiode; a current detection resistor for detecting a current supplied to the first transistor and the photodiode; A diode protection circuit having a simple structure, comprising a first transistor and a second transistor for limiting a current supplied to the photodiode when the detection current of the resistor reaches the limit current. Current can be reliably limited to less than the current limit, and the current That bias voltage is applied to reach the photodiode can be reliably prevented.

According to a sixth aspect of the present invention, in the light quantity measuring method, a current is generated in the photodiode in response to the incident light beam to be measured, and the current generated by the photodiode is amplified by an operational amplifier and output. A light amount measuring method for feeding back a current to be supplied to an input terminal of the operational amplifier to which the photodiode is connected via a predetermined electric resistance, wherein a current supplied to the photodiode is set to a preset current. By limiting the current to the following, if the current limit is set according to the rated current allowed by the photodiode, a current larger than the rated current will flow through the photodiode even if excessive light is incident. Therefore, the destruction of the photodiode can be prevented.

According to a seventh aspect of the present invention, in the light quantity measuring apparatus according to the sixth aspect, a bias voltage having a polarity opposite to a generated current is applied to the photodiode, and a current flowing through the photodiode is reduced. By limiting the bias voltage applied to the photodiode when the current reaches the limit current, the linearity of the characteristics of the photodiode can be improved by the bias voltage, so that a large amount of light can be obtained even when the photodiode has a saturation characteristic. Since the measurement can be performed well and the bias voltage is not applied to the photodiode in which the supplied current has reached the limit current, the breakdown of the photodiode can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a main part of a light quantity measuring device according to an embodiment.

FIG. 2 is a characteristic diagram illustrating a relationship between a light amount incident on a photodiode and an output current.

FIG. 3 is a circuit diagram showing a main part of a light quantity measuring device according to a modified example.

FIG. 4 is a circuit diagram showing a main part of a light quantity measuring device according to a first conventional example.

FIG. 5 is a circuit diagram showing a main part of a light quantity measuring device according to a second conventional example.

[Explanation of symbols]

 21, 41 Light amount measuring device 22 Photodiode 23 First operational amplifier 24 Feedback resistor 25 Constant voltage circuit as diode protection circuit 26 Bias power supply 28 First transistor 29 Current detection resistor 30 Second operational amplifier 32 Second transistor

Claims (7)

[Claims] 1. A photodiode that generates a current in response to the incidence of a light beam to be measured, an operational amplifier that amplifies and outputs a current generated by the photodiode, an output terminal of the operational amplifier, and the photodiode are connected. And a diode protection circuit that limits a current supplied to the photodiode to less than a preset current limit. Light intensity measurement device. A bias power supply for applying a bias voltage having a polarity opposite to a generated current to the photodiode, wherein when the current supplied to the photodiode reaches a limit current, the bias power supply is applied to the photodiode from the bias power supply. The light quantity measuring device according to claim 1, wherein the applied bias voltage is limited by the diode protection circuit. 3. The light quantity measuring device according to claim 1, wherein the diode protection circuit comprises a constant voltage circuit for limiting a current supplied to the photodiode. 4. A second operational amplifier for maintaining the output voltage of the photodiode constant, a first transistor for supplying a current corresponding to an output voltage of the second operational amplifier to the photodiode, A current detection resistor for detecting a current supplied to the first transistor and the photodiode; and a current supplied to the first transistor and the photodiode when a detection current of the current detection resistor reaches a limit current. The light quantity measuring device according to claim 1, further comprising a second transistor for limiting. 5. A second operational amplifier that maintains an output voltage of the photodiode equal to a bias voltage of the bias power supply, and a current corresponding to an output voltage of the second operational amplifier is supplied to the photodiode. A first transistor to be energized; a current detection resistor for detecting a current applied to the first transistor and the photodiode; and a first transistor and the photodiode when a detection current of the current detection resistor reaches a limit current. 3. The light quantity measuring device according to claim 2, further comprising: a second transistor for limiting a current supplied to the second transistor. 6. A current is generated in a photodiode in response to the incidence of a light beam to be measured, the current generated by the photodiode is amplified by an operational amplifier and output, and the output current is passed through a predetermined electric resistance. A method of measuring the amount of light to feed back to the input terminal of the operational amplifier to which the photodiode is connected, wherein the current supplied to the photodiode is limited to a current lower than a preset current. Characteristic light intensity measurement method. 7. A bias voltage having a polarity opposite to that of a generated current is applied to the photodiode, and the bias voltage applied to the photodiode is limited when a current flowing through the photodiode reaches a limit current. 7. The light quantity measuring device according to claim 6, wherein: