JP3267869B2 - Test method of light receiving device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light receiving device provided with a photoelectric conversion element and a signal processing circuit such as an amplifier circuit, and more particularly to an amplifier provided with a current bias circuit for preventing saturation of the amplifier circuit. The present invention relates to a circuit test method.

[0002]

2. Description of the Related Art As shown in FIG. 7, a light receiving device 1 used in an infrared signal receiver for data transmission is a photoelectric conversion element which receives a light signal (infrared signal) and generates a photocurrent signal. It comprises a photodiode 2, an amplifier circuit AMP for amplifying a photocurrent signal, and a comparator 3 for comparing the output of the amplifier circuit AMP with a threshold level Vth.

The amplifier circuit AMP includes a first amplifier 4 as a head amplifier connected to the photodiode 2, and a second amplifier 6 as an AC amplifier connected to the first amplifier 4 via a capacitor 5. The output component due to the low-frequency disturbance light is removed by the second amplifier 6.

In such an infrared signal receiver, as shown in FIG. 8 (a), a pulsed light is emitted from a light emitting element such as a light emitting diode (LED) of the infrared signal transmitter according to a certain rule. When a signal is transmitted, the photodiode 2 receives the optical signal and converts it into a photocurrent signal.

[0005] The photocurrent signal is converted into a voltage by the first amplifier 4 and the second amplifier 6 and amplified, and the amplified output signal is input to the comparator 3. The comparator 3 converts the signal into a threshold level Vt as shown in FIG.
h, a corresponding signal is generated, and the output terminal Vo
Output from Thus, a pulse signal corresponding to the original signal transmitted from the infrared signal transmitter is extracted. In the light receiving device 1, when the photodiode 2 is irradiated with disturbance light such as sunlight or an incandescent lamp, the first amplifier 4 is saturated by the DC photocurrent generated by the disturbance light, and the original signal is The pulse signal cannot be reliably reproduced according to the above.

[0006] When disturbance light enters the photodiode 2 together with the optical signal, as shown in FIG.
This is because a large DC current component is included in the photocurrent signal, and the first amplifier 4 is normally saturated, and normal signal (voltage) cannot be amplified.

Therefore, the amplifier circuit AMP of the light receiving device 1
A DC current supply circuit (auto-bias current control circuit) 7 is provided as a current bias circuit in order to remove a DC current component caused by disturbance light, expand an operation range of the first amplifier 4 and prevent saturation. Have been.

Conventionally, in the above-described wafer test of the light receiving device 1 (test in a wafer state), in a pass / fail test of the DC current supply circuit 7, a voltmeter 8 and a constant current source 9 are connected to the input terminal IN of the light receiving device 1. Are connected, a current is drawn from the input terminal IN (a negative current flows from the input side), and the voltage at the input terminal IN of the light receiving device 1 at that time is measured by the voltmeter 8. The quality of the DC current supply circuit 7 is determined based on whether or not the magnitude of the measured value of the voltage is normal.

[0009]

However, in the test method for judging the quality of the DC current supply circuit 7 as described above, even when the voltage at the input terminal IN of the light receiving device 1 is normal, the DC current supply If the capacity of the circuit 7 is insufficient, the first amplifier 4 is saturated, and the light receiving device 1 may not operate normally. This makes it impossible to accurately determine whether the DC current supply circuit 7 is good or not.

In the light receiving device 1 as described above,
When obtaining the amplifier gain (amplification gain) of the amplifier circuit AMP, a predetermined signal is input from the input terminal IN of the light receiving device 1 and the signal output from the output terminal Amp-Out of the amplifier circuit AMP is directly measured and obtained. The light receiving device 1
Is in a wafer state, the measurement is difficult due to the influence of the surrounding noise environment and the like.

In view of the above, the present invention provides a method for testing a light receiving device capable of accurately measuring the capability of a current bias circuit and obtaining the amplifier gain of an amplifier circuit without being affected by a surrounding noise environment or the like. The purpose is to provide.

[0012]

Means for solving the above problems include a photoelectric conversion element for converting light into a current, an amplifier circuit for amplifying the current converted by the photoelectric conversion element, and a current bias circuit for preventing saturation of the amplifier circuit. In the light receiving device provided with the above, the output voltage of the amplifier circuit is measured a plurality of times by operating the amplifier circuit, and the quality of the current bias circuit is determined based on the dispersion of the variation of the measured value. As a result, there is a case where the current bias circuit is halfway in spite of the fact that the output of the amplifier circuit is normal. In such a case, the quality of the current bias circuit can be accurately determined.

At this time, there is a correlation between the variation in the measured value and the amplifier gain of the amplifier circuit, and the amplifier gain can be obtained indirectly only by measuring the output voltage of the amplifier circuit.

Further, in the above-described method for testing a light receiving device, when a constant current source is connected to the input terminal of the light receiving device to operate the amplifier circuit, the current flowing through the input terminal of the light receiving device can be made constant. The adverse effect due to the fluctuation of the input current input to the circuit is reduced.

Even if the light receiving device has a photoelectric conversion element, an amplifier circuit, and a current bias circuit integrated in the same chip, when the photoelectric conversion element is irradiated with light to operate the amplifier circuit, the same as described above is obtained. In addition, the quality of the current bias circuit can be accurately determined, and the amplifier gain of the amplifier circuit can be easily and indirectly measured without being affected by the noise environment around the light receiving device. Further, it is not necessary to connect a constant current source for operating the amplifier circuit to the light receiving device, and the test of the photoelectric conversion element can be performed at the same time.

At this time, if the light irradiated to the photoelectric conversion element is detected and controlled so that the light amount becomes constant, a test with good reproducibility can be performed, and the adverse effect due to the fluctuation of the input current input to the amplifier circuit is reduced. Thus, the test can be performed accurately.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) A light receiving device 1 of this embodiment includes a photodiode 2, an amplifier circuit AMP, a comparator 3, and a DC current supply circuit 7, and is the same as the conventional one shown in FIG. is there. In order to perform a wafer test of the amplifier circuit AMP, in the present embodiment, the voltmeter 8 is not connected to the input terminal IN of the light receiving device 1 as in the wafer test of the conventional light receiving device 1, but in FIG. As shown in
The voltmeter 8 is connected to the output terminal Amp-Out of the amplifier circuit AMP, and a DC current is supplied from the input terminal IN by the constant current source 9 (a current is extracted from the input side or a current is supplied to the input side). Activate the circuit AMP,
The output voltage (amplifier output DC voltage) of the amplifier circuit AMP at that time is measured by the voltmeter 8. At this time, since the current is supplied by the constant current source 9, a very stable current can flow. The connection of the voltmeter 8 and the connection of the constant current source 9 to the light receiving device 1 are performed via a probe card. The probe card is an electrical device for bringing an external measuring instrument or the like into contact with a test pad of a circuit via a probe during a test.

First, a current is supplied to the input terminal IN, and a DC voltage output from the amplifier at that time is measured by the voltmeter 8. Then, the measured value of the voltage at this time is compared with the voltage value in the normal state to determine whether or not the amplifier circuit AMP is normal.

Here, as shown in FIG. 2, the correlation between the input current to the light receiving device 1 and the amplifier gain of the amplifier circuit AMP increases as the light receiving device 1 is non-defective. The decrease in the amplifier gain at the time is gradual. On the other hand, if the product is defective, the amplifier gain decreases in inverse proportion to the input current.

If it is determined that the result is not normal,
As a test failure, red ink (Bad Mark) is applied to indicate that the light receiving device 1 is defective. Then, the test of the light receiving device 1 is completed, and the process proceeds to a test of another light receiving device 1. If the measured value of the amplifier output DC voltage is not normal, the following measurement cannot be performed correctly.

If the result of the determination of the measured value is normal, the amplifier output DC voltage is continuously measured a plurality of times (for example, about 10 times).

At this time, when the DC current supply circuit 7 is normal, looking at the amplifier output DC voltage waveform of the input current value at point a in FIG.
Becomes large, and the measured value varies when the amplifier output DC voltage is measured a plurality of times (for example, 10 times). When the DC current supply circuit 7 is defective despite the normality of the amplifier output DC voltage, the amplifier output DC voltage waveform of the input current value at point b in FIG. As shown, the amplitude B2 is small, and the variation in the measured value when the amplifier output DC voltage is measured a plurality of times (for example, 10 times) is small.

This is because if the first amplifier 4 is operating normally without being saturated, that is, if the DC current supply circuit 7 is functioning normally, the voltage on the output side of the second amplifier 6 will have noise. (Noise generated from the amplifier circuit AMP itself)
Occurs, the measured value of the amplifier output DC voltage varies, and a large variance occurs.

On the other hand, when the first amplifier 4 is saturated and is not operating normally, that is, when the DC current supply circuit 7
Is insufficient, the noise generated on the output side of the second amplifier 6 becomes smaller, the variation in the measured value of the amplifier output DC voltage becomes smaller, and the variance becomes smaller.

Thus, the quality of the DC current supply circuit 7 can be determined from the variance of the measured values. The variance can be obtained from the following equation from the measured value x of the amplifier output DC voltage and the number of measurements n.

[0026]

(Equation 1)

Therefore, by comparing the dispersion value obtained by the above equation with the dispersion value when the DC current supply circuit 7 is normal or the dispersion value when the DC current supply circuit 7 is defective, the DC current supply circuit 7, the quality of the light receiving device 1 is finally distinguished from the defective product.

FIG. 4 shows a correlation between the amplitude of the DC voltage waveform of the amplifier output (the amplitude of the measurement variation) and the amplifier gain of the amplifier circuit AMP. This shows that the amplifier gain is proportional to the amplitude of the measurement variation. Therefore, the amplifier output DC voltage is measured, and if the amplitude of the measurement variation is known, the amplifier gain can be obtained. That is, the amplifier gain can be obtained indirectly from the amplitude of the measurement variation.

As described above, the current flows to the input terminal IN of the light receiving device 1 to drive the amplifier circuit AMP, and the output terminal A
Only by measuring the amplifier output DC voltage output from mp-Out a plurality of times, the quality of the DC current supply circuit 7 can be accurately determined from the dispersion of the variation of the measured value. Therefore, the current supply capability of the DC current supply circuit 7 can be tested by a simple method.

Furthermore, since there is a correlation between the amplitude of the variation of the measured value and the amplifier gain, the amplifier gain can be accurately and easily obtained without being affected by the noise environment without performing a special measurement.

Further, since a current is supplied from the constant current source 9 to the input terminal IN of the light receiving device 1 and the DC voltage output from the amplifier is measured, the adverse effect due to the fluctuation of the input current is reduced, and the stable light receiving device 1 is obtained. Test is possible.

Further, it is possible to judge the quality of the entire circuit by the first measurement of the amplifier output DC voltage, and if it fails, there is no need to perform the next unnecessary test, and the test can be performed very efficiently.

(Second Embodiment) The light receiving device 1 of the present embodiment is configured by integrating a signal processing circuit such as a photodiode 2, an amplifier circuit AMP, a DC current supply circuit 7, and a comparator 3 in the same chip. . In the wafer test of the monolithic light-receiving device 1, as shown in FIG. 5, light (P) is directly irradiated on the photodiode 2 by the light-emitting diode (LED) 20, and a photocurrent signal is generated. It draws current from the input side. LED
The constant current source 9 is connected to 20, and is driven by supplying a constant current from the constant current source 9. The other components are the same as those of the first embodiment, and the same components are denoted by the same reference numerals.

With such a configuration, the LED 20 is driven to emit light, the photodiode 2 receives the light, converts the light into a photocurrent, and operates the amplifier circuit AMP by the photocurrent. Then, the amplifier output DC voltage output to the output terminal Amp-Out of the amplifier circuit AMP at this time is measured by the voltmeter 8. At this time, if there is no amplifier output DC voltage, it can be determined that the photodiode 2 is malfunctioning.

Thereafter, as in the first embodiment, it is determined whether or not the circuit of the light receiving device 1 is normal from the measured values. If normal, measure the amplifier output DC voltage several times (for example, about 10 times)
The variance of the variation in the measured values is obtained, and the quality of the DC current supply circuit 7 is determined. Further, the amplifier gain is indirectly obtained from the amplitude of the variation of the measured value.

At this time, as shown in FIG. 6, light from the LED 20 radiated to the photodiode 2 is applied to the probe card 2.
1 is detected by the monitoring photodiode 22 provided on the first side. The control circuit or the like controls the LED so that the amount of light radiated to the photodiode 2 becomes constant.
20 is controlled.

As described above, by irradiating the photodiode 2 with light, a current flows through the light receiving device 1 to drive the amplifying circuit AMP. The pass / fail judgment can be made accurately, and the amplifier gain of the amplifier circuit AMP can be easily obtained without being affected by the noise environment around the light receiving device 1.

Further, it is not necessary to connect the constant current source 9 or the like, which is a current source for operating the amplifier circuit AMP, to the light receiving device 1, and the test of whether or not the photodiode 2 operates can be performed at the same time. The test time of the light receiving device 1 can be reduced.

Further, since the light applied to the photodiode 2 is detected and the light amount is controlled so as to be constant, accurate and reproducible measurement can be performed. Therefore, the variation of the amplifier output DC voltage due to the change in the amount of light applied to the photodiode 2 is reduced, and an accurate test can be performed.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that many modifications and changes can be made to the above-described embodiment within the scope of the present invention. For example, also in the first embodiment, the amplifier circuit may be operated by irradiating light to the photodiode. Further, a voltmeter may be connected between the first amplifier and the second amplifier to measure the amplifier output DC voltage.

[0041]

As is apparent from the above description, according to the present invention, the current bias is obtained by operating the amplifier circuit of the light receiving device, measuring the output voltage thereof a plurality of times, and obtaining the dispersion of the measured values. The quality of the circuit can be accurately and easily determined. Further, since the variation in the measured value corresponds to the amplifier gain, it is not necessary to perform a test for measuring the amplifier gain, and the amplifier gain can be easily obtained.

Further, since the output voltage is measured by connecting the constant current source to the input terminal of the light receiving device and operating the amplifier circuit, the adverse effect due to the fluctuation of the input current is reduced, and the stable test of the light receiving device is performed. Becomes possible.

For the monolithic light receiving device, the amplifier circuit is operated by irradiating the photoelectric conversion element with light, so that there is no need to connect a constant current source to the light receiving device. In addition, since the test for the operation of the photoelectric conversion element can be performed at the same time, the test time of the light receiving device can be reduced.

Further, since the light irradiated on the photoelectric conversion element is detected and controlled so that the light amount becomes constant, accurate and reproducible measurement can be performed. Therefore, a change in the output voltage of the light receiving device due to a change in the amount of light applied to the photoelectric conversion element is reduced, and an accurate test can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an equivalent circuit and a test circuit of a light receiving device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between an amplifier gain and an input DC current.

3A and 3B are diagrams illustrating an amplifier output DC voltage waveform of an amplifier circuit. FIG. 3A illustrates a case where a DC current supply circuit is normal.
(B) is when the DC current supply circuit is defective

FIG. 4 is a diagram showing a relationship between amplitude of measurement variation and amplifier gain;

FIG. 5 is a diagram showing an equivalent circuit and a test circuit of the light receiving device according to the second embodiment.

FIG. 6 is a schematic diagram when a probe card is used.

FIG. 7 is a diagram showing an equivalent circuit and a test circuit of a conventional light receiving device.

8A and 8B show waveforms of a photocurrent signal; FIG. 8A shows a waveform when there is no disturbance light; FIG. 8B shows a waveform when disturbance light is mixed;

FIG. 9 is a diagram showing an output of a second amplifier and an output of a comparator.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light receiving device 2 photodiode 4 first amplifier 6 second amplifier 7 DC current amplifier circuit 8 voltmeter 9 constant current source 20 LED 21 probe card AMP amplifier circuit

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01R 31/00 G01J 1/00 G01R 31/26

Claims (5)

(57) [Claims] A photoelectric conversion element for converting light into a current; an amplifier circuit for amplifying the current converted by the photoelectric conversion element;
In a light receiving device including a current bias circuit for preventing saturation of the amplifier circuit, the output voltage of the amplifier circuit is measured a plurality of times by operating the amplifier circuit, and the quality of the current bias circuit is determined based on the dispersion of measured values. A method for testing a light receiving device, the method being performed. 2. A photoelectric conversion element for converting light into a current, an amplifier circuit for amplifying the current converted by the photoelectric conversion element,
In a light receiving device including a current bias circuit for preventing saturation of the amplifier circuit, the output voltage of the amplifier circuit is measured a plurality of times by operating the amplifier circuit, and the indirect measurement of the amplifier gain of the amplifier circuit is performed based on a variation in measured values. A method for testing a light receiving device. 3. The test method for a light receiving device according to claim 1, wherein a constant current source is connected to an input terminal of the light receiving device to operate the amplifier circuit. 4. The light-receiving device according to claim 1, wherein the photoelectric conversion element, the amplifier circuit, and the current bias circuit are integrated in a same chip, and the light-receiving element irradiates light to operate the amplifier circuit. 3. The test method for a light receiving device according to claim 1, wherein the test is performed. 5. The test method for a light receiving device according to claim 4, wherein the light irradiated to the photoelectric conversion element is detected, and the light quantity is controlled to be constant.