JPH054010B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a photometry device that can perform accurate photometry over a wide range from low current range to high current range. 2. Description of the Related Art In recent years, it has become necessary for photometric devices to detect over a wide range from low current ranges to high current ranges. On the other hand, light-receiving elements have also been realized that exhibit linearity over a wide range. In a conventional photometry device, when performing photometry over a wide range from a low current range to a high current range, feedback resistors 19, 20, and 21 with different resistance values are used as shown in Figure 4a. By changing the degree changeover switch 22, the amount of feedback is changed,
This was handled by changing the amplification degree of the operational amplifier 18. Further, as shown in FIG. 4(b), the same level of amplification as that in FIG. 4(a) can be obtained and the number of feedback resistors can be reduced. This circuit uses feedback resistors 26 and 27 with different resistance values and a voltage divider 25 that divides the output of the operational amplifier 24, and changes the amount of feedback by changing the amplification changeover switches 28 and 29. It changes the degree. Problems to be Solved by the Invention However, in such a conventional photometric device, as shown in FIG. 4a, the feedback resistors 19, 20,
When attempting to change the degree of amplification by changing the resistance value of feedback resistors 19, 20, and 21, it is necessary to widen the range of change in the resistance values of feedback resistors 19, 20, and 21 in order to accommodate photometry of a wide incident light area. The maximum resistance value increases. If the resistance value becomes too large, it will easily pick up surrounding noise and will be affected by leakage current, making it impossible to accurately switch the amplification level, which will naturally limit the photometry range by switching the amplification level. . Figure 4b shows an example of improving such problems.
There is a photometric circuit shown in the figure below. In FIG. 4b, the amplification degree can be switched in the following manner. Suppose that the feedback resistors 26, 27, the voltage dividing resistor 25a,
The resistance value ratio of 25b is 10:1 and 99:1, respectively.
Suppose we set At this time, the lowest amplification degree is obtained with the amplification degree changeover switch 28 at point b and the amplification degree changeover switch 29 at point c. Next, by switching the amplification degree changeover switch 28 to point a, an amplification degree of 10 times can be obtained. Furthermore, when trying to obtain an amplification degree of 100 times 1000 times, a feedback resistor with a resistance value of 100 times 1000 times is required in Figure 4a, but in Figure 4b, a feedback resistor with a resistance value of 100 times 1000 times is required. Since the ratio of the resistance values is 99:1, by switching the amplification degree changeover switch 29, an amplification degree of 100 times 1000 times can be obtained.
Therefore, the amplification degree can be changed without increasing the resistance value of the feedback resistor as shown in FIG. 2a.
However, at this time, unless the resistance values of the feedback resistors 26 and 27 are much larger than the resistance value of the voltage dividing resistor 25b, the voltage dividing resistor 25b will affect the feedback resistors 26 and 27. For example, in the case of the feedback resistor 26 and the voltage dividing resistor 25b, the amount of feedback in the feedback loop of the operational amplifier 24 is 1/2, so it is possible to accurately change the amplification degree by switching the voltage dividing resistors 25a and 25b. I can't do it anymore. Therefore, if the resistance values of the feedback resistors 26 and 27 are increased to such an extent that the influence of the voltage dividing resistor 25b is not exerted on the feedback resistors 26 and 27, it becomes easier to pick up surrounding noise, as shown in Fig. 4a. Accurate amplification cannot be expected because it is affected by leakage current. The present invention solves the above problems and enables accurate photometry over a wide range from low current ranges to high current ranges. Means for Solving the Problems The present invention solves these conventional problems, and includes a photoelectric conversion element that generates a current according to the amount of incident light, an operational amplifier that amplifies the photocurrent of the photoelectric conversion element, and an operational amplifier that amplifies the photocurrent of the photoelectric conversion element. , a voltage divider that divides the output of the operational amplifier;
a plurality of feedback resistors having one end connected to the input of the operational amplifier, a changeover switch for switching the plurality of feedback resistances, a changeover switch for switching between the operational amplifier output and the voltage divider output, and a switch provided between the two changeover switches. By configuring the feedback resistor with impedance conversion means, it is possible to set the feedback resistor to a resistance value that is not affected by noise or leakage current, and to perform accurate photometry over a wide range from low current range to high current range. It is something that Effect The present invention has a photometric device configured as described above, so that the output that is incident on the photoelectric conversion element and amplified by the operational amplifier is controlled by a voltage dividing resistor, and is fed back through the impedance conversion means and the feedback resistor. In the case of the amplification means, the influence of the voltage dividing resistor on the feedback resistance is eliminated by the impedance conversion means, and accurate photometry is performed over a wide range from low current to high current. Embodiment FIG. 1 shows a photometric device in an embodiment of the present invention. In FIG. 1, 1 is a photoelectric conversion element, 2 is an operational amplifier, 3 is a voltage divider, 4 and 5 are feedback resistors, 6,
Reference numeral 7 denotes amplification changeover switches a and b, 8 an impedance conversion means, 9 a control circuit for the amplification changeover switches a6 and b7, and 10 and 11 resistors. FIG. 1 shows an example in which a non-inverting amplifier circuit using an operational amplifier is used as the impedance conversion means. Also, Figure 1 shows the photometry circuit when switching the amplification degree in four stages, and Figure 2 shows the relationship between the amplification degree changeover switch a6 and the amplification degree changeover switch b7 when changing the amplification degree depending on the level of incident light. Shown below. When light is incident on the photoelectric conversion element 1 in such a photometric circuit, a photocurrent is generated depending on the amount of incident light. The generated photocurrent is amplified by an operational amplifier 2 and converted into a voltage value. The output of operational amplifier 2 is
The voltage is divided by the voltage divider 3 according to the ratio of the resistance values of the voltage dividing resistors 3a and 3b, passes through the impedance converting means 8, and is fed back by the feedback resistors 4 and 5. The degree of amplification at this time is determined by the ratio of the resistance values of the voltage dividing resistors 3a and 3b and the amount of feedback fed back by the feedback resistors 4 and 5.
The method for switching the amplification degree will be described in detail below. In Figure 1, feedback resistors 4 and 5, voltage dividing resistor 3
The ratio of the resistance values of a and 3b is set to 10:1 and 99:1, respectively. Further, in FIG. 2 and the table below, when the amplification degree is lowered as the current range changes from the low current range to the high current range, the ranges to be switched are set as 1, 2, 3, and 4 in order from the low current range. High amplification is required for photometry in the low current range. Therefore, in the lowest range 1, the contact point of the amplification degree changeover switch a6 is set to the point a, and the contact point of the amplification degree changeover switch b7 is set to the point d, thereby obtaining the highest amplification degree. Next, as the current range increases, the amplification degree is lowered, so when in range 2, by switching the contact point of amplification changeover switch a6 to point b, the ratio of the resistance values of feedback resistors 4 and 5 is set to 10:1. Therefore, the amplification degree is lowered to 1/10. Next, when in range 3, the ratio of the resistance values of the voltage dividing resistors 3a and 3b is set to 99:1 by switching the contact of the amplification changeover switch a6 to point a and the contact of the amplification changeover switch b7 to point c. For some reason, the amplification level drops to 1/100 of its initial value. Furthermore, when in range 4, the amplification changeover switch a
By switching contact point 6 to point b, the amplification degree can be reduced to 1/1000 of the initial value. In this way, by changing the amplification degree according to the current range, photometry is performed while always maintaining a constant output range. Also, at this time, since the input impedance of the impedance conversion means 8 is so large that it can be considered infinite and the output impedance is so small that it can be considered 0, the resistance value of the voltage dividing resistor 3b does not affect the feedback resistors 4 and 5.
It is possible to accurately divide the voltage based on the ratio of the resistance values of the voltage dividing resistors 3a and 3b. In the embodiment of the present invention, an operational amplifier whose input impedance is so large that it can be regarded as infinite and whose output impedance is so small that it can be regarded as 0 is used as the impedance conversion means. As long as it is much larger than the voltage dividing resistor 3b and the feedback resistors 4 and 5 are much larger than the output impedance, it is possible to replace it with another one without using the operational amplifier as in the embodiment of the present invention. It is.

[Table] Next, select the amplification degree changeover switches a6 and b7.
The third example of the control circuit 9 that controls the operation of the
This will be explained using figures. 12, 13 in Figure 3
is a voltage comparator, 14 is an up/down counter, and 15 and 16 are relays. The voltage comparator 12 has the role of detecting the level at which the amplification degree is decreased, and the up-down counter 1
It is connected to the count up terminal (CU) of 4. On the other hand, the voltage comparator 13 has the role of detecting the level that increases the amplification degree, and the countdown terminal (CD) of the up-down counter 14
It is connected to the. The up-down counter 14 serves to generate a coded amplification signal. This amplification degree signal operates relays 15 and 16, and amplification changeover switches a6 and b7 are operated.
The degree of amplification is changed by switching. next,
The operation when the photocurrent changes will be explained using FIGS. 1, 2, and 3. In FIG. 1, when the photocurrent of the photoelectric conversion element 1 increases, the output voltage of the operational amplifier 2 increases.
When this reaches a certain value, the voltage comparator 12 operates to lower the amplification degree, and the up-down counter 14 increments the count by one. By default, the output of the up-down counter 14 is set to the coded amplification signal A=0, B=0, and in this state, the contact of the amplification changeover switch a6 is at point a and the contact of amplification changeover switch b7 is at point d. Set the state to be . When the count input from the voltage comparator 12 enters the up-down counter 14, the coded amplification signal changes to A=1 and B=0. By changing A=1, relay 1
5 operates and switches the contact point of the amplification degree changeover switch a6 to point b. This operation causes feedback resistance 4
From the relationship between the resistance values of and 5, the amplification degree is 1/10. When the photocurrent further increases, the voltage comparator 12 operates in the same manner, causing the up-down counter 14 to count up by one, and coded amplification signals A=0 and B=1 are obtained. In response to this signal, relays 15 and 16 operate, and the contact point of the amplification degree changeover switch a6 becomes the point a, and the contact point of the amplification degree changeover switch b7 becomes the point c, and the amplification degree becomes 1/100 of the initial amplification degree. When the photocurrent further increases, the contact point of the amplification degree changeover switch a6 becomes the point b and the contact point of the amplification degree changeover switch b7 becomes the point c due to the same operation, and the amplification degree becomes 1/1000 of the initial amplification degree.
(The relationship between the amplification degree changeover switches a6 and b7 is shown in FIG. 2) In this way, the amplification degree can be changed depending on the level of the photocurrent. Furthermore, in this embodiment, the case where the amplification degree is four stages has been explained, but if the photometry range becomes wider and it becomes necessary to increase the number of amplification changes, the feedback resistance of the operational amplifier 2 can be increased.
By changing the ratio of the voltage dividing resistors 3a and 3b and adding an amplification switching switch a6, the up-down counter 1
The number of bits of the coded amplification signal of 4 may be increased. In this embodiment, the impedance conversion means 8
In the non-inverting circuit of the operational amplifier used as
Resistors 10 and 11 are provided, and by changing the resistance value, the amplification degree of the operational amplifier can be changed, so a correction coefficient can be applied to the amplified output of the photometric circuit, and the photoelectric conversion element 1 Measurement errors due to dirt or deterioration can be compensated for. Effects of the Invention As described above, the present invention can be applied over a wide range from low current range to high current range without increasing the number of feedback resistors or increasing the resistance value, which may cause measurement errors. Therefore, accurate photometry can be performed while switching the amplification degree.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a photometric device according to an embodiment of the present invention, Fig. 2 is a diagram showing amplification switching according to the measurement range of the device and the state of the amplification switching switch, and Fig. 3 is a diagram showing the amplification of the device. FIGS. 4a and 4b are block diagrams showing a control circuit for a degree changeover switch, and FIGS. 4a and 4b are circuit diagrams of a conventional photometric device. 1...Photoelectric conversion element, 2...Operation amplifier, 3...
...Voltage divider, 4...Feedback resistor, 5...Feedback resistor, 6
...Amplification degree changeover switch a, 7...Amplification degree changeover switch b, 8...Impedance conversion means, 9...Control circuit, 10...Resistor, 11...Resistor.

Claims (1)

[Claims] 1. A photoelectric conversion element that generates a current according to the amount of incident light, an operational amplifier that amplifies the photocurrent of the photoelectric conversion element, a voltage divider that divides the output of the operational amplifier, and a plurality of devices having one end connected to the input of the operational amplifier. A photometric device comprising: a feedback resistor; a switch for switching between the plurality of feedback resistors; a switch for switching between the operational amplifier output and the voltage divider output; and impedance conversion means provided between the switch.