JPH0321829A - Photometry device - Google Patents

Abstract

PURPOSE:To eliminate the need of the correction of a temperature by providing a photoelectric current/voltage conversion circuit, a reference voltage circuit and a differential amplification circuit whose amplification factor has characteristic in inverse proportion to the temperature. CONSTITUTION:A light input sensor 100 detects incident light and the photoelectric current/voltage conversion circuit 110 is connected to the sensor 100 to convert a photovoltaic current into a voltage. The reference voltage circuit 120 converts a constant-current having the constant temperature into the voltage. The amplification factor of the differential amplification circuit 140 has the characteristic in inverse proportion to the temperature and receives output from both circuits 110 and 120 in its differential input terminal, then outputs a difference voltage between output from both of them. Thus, the amplification factor is in reverse proportion to the temperature and the input voltage in proportion to the temperature can be amplified with the amplification factor in reverse proportion to the temperature, so that the output voltage can be made constant to the temperature. As a result, the correction at each temperature is not needed and a circuit for the correction is made unnecessary.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improving the temperature characteristics of a photometric device used in an exposure meter or the like.

[Conventional technology]

FIG. 3 is a diagram showing a conventional photometric device. In the figure,
100 is a light input sensor that generates a photovoltaic current in proportion to the amount of incident light. 5, 6.10 is an operational amplifier. 3.
4 is a current logarithm compression diode, which constitutes a photocurrent-voltage conversion circuit 110 that converts a photovoltaic current into voltage using an operational amplifier 5 and a diode 3. 7 is a constant current source that outputs a constant current that is constant with respect to temperature, and a diode 4, an operational amplifier 6, and a constant current source 7 constitute a second reference voltage circuit l20. 11.12.13 are resistors, resistors 12,1
3 and the operational amplifier 10 constitute a differential amplifier circuit 140 whose amplification factor is constant with respect to temperature. 8 is a photometric device output terminal.

9 is a negative power supply, and the photometric output is output as a voltage between the output terminal 8 and the negative power supply 9. 130 is a first reference voltage circuit that serves as a reference voltage for the operational amplifier 6 and a reference voltage for the differential amplifier circuit 140.

Next, the operation will be explained.

If the voltage of the first reference voltage circuit 130 is v3, then the second
The voltage v output to the output terminal 2 of the reference voltage circuit 120 of
2 is Vz = V, +Vt in (Io /Is)
−(1). Here, Va=k-T/q. Further, k is Boltzmann's constant, T is absolute temperature, q is the amount of electron charge, and Is is the reverse saturation current of the transistor.

Now, the magnitude of the photovoltaic current generated by the optical input sensor is
Then, the voltage VI generated at the output terminal 1 of the photocurrent voltage conversion circuit 110 is V, ==Vz −v, In(IL/Is)=Vs
+VT l'n(Io /Is) Vy In(It
/Is)=V, +VyIn(Io/IL)
-(2), which becomes the non-inverting terminal side input of the differential amplifier circuit 140.

Resistor 12.1 that determines the amplification factor of the differential amplifier circuit 140
The resistance values of 3 are R, , R. Then, the voltage ■ output to the output terminal 8 of the photometric device. LIT is Voui = (V+ -Vs) (1 +Rz /R
+) 10Vs””Vt (1 +Rz /R+
) In (IO/IL)+Vs
...(3) Here, Vs-a - VT
(a: constant), equation (3) is Vo = Vt ((1 +Rz /R+) In
(Io/It)+a) ・
...(4). If Io, 11, a is constant with respect to temperature, and the temperature coefficients of Rr and Rt are the same, then V
o is proportional to T. [Problems to be Solved by the Invention] Since conventional photometric devices are configured as described above, it has been necessary to correct the voltage output from the photometric device at each temperature. This invention was made to solve the above-mentioned problems. Under the condition of the same amount of human irradiation, the output voltage of the photometer can be kept constant regardless of temperature changes, and it eliminates the need for correction at each temperature. The purpose is to obtain a photometric device that does not require [Means for Solving the Problems] A photometric device according to the present invention is provided with a photocurrent-voltage conversion circuit and a reference voltage circuit that converts a constant current at a constant temperature into a voltage, and the differential input terminals thereof are provided with each of the above-mentioned devices. A differential amplifier is provided to which the output of the circuit is connected and amplifies the voltage difference between the two outputs by a certain amplification factor, and the amplification factor has a characteristic that the amplification factor is inversely proportional to the temperature.

[Effect]

In this invention, instead of the conventional constant temperature differential amplifier circuit in which the amplification factor is constant with respect to temperature, a temperature inversely proportional differential amplifier circuit is used. It can be amplified with an inversely proportional amplification factor, and as a result, the output voltage can be made constant with respect to temperature.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit configuration diagram for explaining the principle of a photometric device according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a temperature inversely proportional differential amplifier circuit of this photometric device. In FIG. 1, 140 is a temperature inversely proportional differential amplifier circuit, and other parts that are equivalent to the conventional example shown in FIG. 3 are designated by the same symbols. In Figure 2, 1 and 2 are differential input terminals, 21 and 22
．． 26-29, 32.33 are transistors, 17.18
is a diode, 23, 24, 39 is a resistor, 25, 37 is a bias constant current source, 40 is a reference voltage source, and 41 is an operational amplifier. In FIG. 1, the output terminal 1 of the photocurrent voltage conversion circuit 110 and the output terminal 2 of the second reference voltage circuit 120 are respectively connected to the input of a temperature inversely proportional differential amplifier circuit 140. The output terminal 8 of the photometric device is connected to the output of . In FIG. 2, the photocurrent-voltage conversion circuit output connection terminal 1 and the second reference voltage circuit output connection terminal 2 are connected to the bases of NPN transistors 21.22 and diodes 17.2, respectively. 1B, the first differential amplifier circuit 200 is blocked by resistors 23 and 24. Above transistor 2
Resistors 23 and 24 are connected to the wires 1 and 22, respectively, and the other ends of these resistors 23 and 24 are connected to each other and to a constant current source 25 for bias. The collectors of the transistors 21 and 22 are connected to the power supply l6 via diodes 17 and 18, respectively, and are connected to the NPN transistors constituting the second differential amplifier circuit 210.
Connected to the bases of transistors 32 and 33. This second differential amplifier circuit 210 is composed of two first current mirrors 30 and 31, a second current mirror 36, a bias constant current source 37, and NPN} transistors 32 and 33. The emitters of 32 and 33 are connected in common and a bias constant current source 37
It is connected to the. Further, the collectors of the transistors 32 and 33 are respectively connected to two first current ξ rollers 30 and 31. The current mirror 30 is a PNP transistor 26.2
7, and the collector of the transistor 26 is connected to a second current mirror 36. This second
The current mirror 36 is an NPN transistor 34.35
The collector of the transistor 35 and the collector of the PNP transistor 29 that connects the first current mirror 31 are connected in common, and are also connected to the inverting terminal of the operational amplifier 41 and the feedback resistor 39.

Note that this connection point is 38. Further, a constant temperature reference voltage source 40 is connected to the non-inverting terminal of the operational amplifier 4l, and a feedback resistor 39 is connected between the output terminal and the inverting terminal of the operational amplifier 41 to form a current-voltage conversion circuit 220. ing.

Next, we will explain the operation. In FIG. 1, if the photovoltaic current generated by the incident light is 1, then the output voltage Va of the photocurrent-voltage conversion circuit 110 is V, =V r Vt In (It /1 m )
''(5).Here, Vr is the voltage value of the first reference voltage circuit 130.Next, when calculating the output voltage V of the second reference voltage circuit 120, Vb-Vr-Vtln( Io/l) (6) Therefore, the differential voltage Vi input to the temperature inversely proportional differential amplifier circuit 140 is Vi+-V.Vb-VtIn (Io/I L
)...(7). In other words, this differential voltage vi, is input to the first differential amplifier circuit 200 in FIG. Next, the operation of the temperature inversely proportional differential amplifier circuit shown in FIG. 2 will be explained.

The amplification degree G at the small signal differential input of the first differential amplifier circuit 200 is as follows. Here, gm is the mutual conductance of the transistor, expressed as (I a /2) /vt. Therefore, equation (8) becomes. Next, if we calculate the change in the above amplification degree G with respect to temperature, we get aT (2 X Vt + IAX Rt) "l. Here, αE and αIA are the temperature coefficients of the resistor RE and bias constant current source ■1, respectively. is.α+a=1/
When the condition is set to T-α, the above G(+) equation becomes, and the amplification degree G of the first differential amplifier circuit 200 becomes constant with respect to temperature.

Next, consider the output voltage at the photometer output terminal 8 when a differential voltage vh is applied to the second differential amplifier circuit 210. vi. The collector currents of the transistors 32 and 33 forming the differential circuit configuration when a differential voltage of , the amount of displacement of the output voltage is Vo, and the reference voltage of the constant temperature reference voltage source 4o is 3, the following relationship holds true. I m -It -tl, . ...02) Vo
-1oXRo=RoX (I II z)
-(13)■1=VTXln. -Q4)It, and the above GZ. 03). From equation (14), the output voltage V of the photometer output terminal 8 is obtained. ．． j7 becomes. Next, if we calculate the amount of change in equation 00 with respect to temperature, we get. Also, (7). (From the IQ formula, Viz = G
Vr Xln (Io/It) αvi− −
1 /T '''Q7) Also, let the temperature coefficient αII of the bias constant current source 37 be 1 α, and substitute this into the above equation 06) along with the equation 0'7).Therefore, as shown in the OI equation, It can be seen that the output voltage of the photometric device does not change depending on the temperature when the amount of incident light is the same.In this example, in place of the conventional constant temperature type differential amplifier circuit, a temperature inversely proportional type differential amplifier circuit is used. Because we used an amplifier circuit,
The amplification factor is inversely proportional to the temperature. This allows the input voltage, which is proportional to the temperature, to be amplified by the inversely proportional amplification factor. As a result, the output voltage remains constant with respect to the temperature. can do. As a result, there is no need to make corrections at each temperature, and a circuit for making corrections can be made unnecessary. [Effects of the Invention] As described above, the photometric device according to the present invention includes a photocurrent-voltage conversion circuit that converts photovoltaic current into voltage and a reference voltage circuit that always outputs a constant voltage. A differential amplifier whose amplification factor is inversely proportional to temperature is provided, and the outputs of each of the above circuits are connected to the differential input terminals of the differential amplifier, and the differential voltage between the two outputs is amplified and output. The output voltage of becomes constant with respect to temperature,
As a result, there is no need to make corrections at each temperature,
This has the effect of eliminating the need for a circuit for correction.

[Brief explanation of drawings]

FIG. 1 is a principle diagram showing a photometric device according to an embodiment of the present invention, FIG. 2 is a specific circuit diagram showing a temperature inverse proportional differential amplifier of this photometric device, and FIG. 3 is a diagram showing a conventional photometric device. FIG. In FIG. 1, 100 is an optical input sensor, 110 is a photocurrent voltage conversion circuit, 120 is a reference voltage circuit, and 140 is a differential amplifier circuit. In FIG. 2, 200 is a first differential amplifier circuit, 210
2 is a second differential amplifier circuit; 220 is a current-voltage conversion circuit;
5.37 is a constant current source for bias, 21.22 is a first differential transistor, 32.33 is a 20th differential transistor, 30.31 is a first current mirror, 36 is a second current mirror, 40 is the reference voltage source, and 4 is the operational amplifier (
operational amplifier), 11 to 13.23, and 24.39 are resistors.

Claims (1)

[Claims] (1) A photometric device that outputs a voltage according to the intensity of incident light, comprising: a light input sensor that detects incident light; a photocurrent-voltage conversion circuit that is connected to the light input sensor and converts photovoltaic current into voltage; and temperature. A reference voltage circuit that converts a constant current into voltage, whose amplification factor is inversely proportional to temperature, receives the outputs of both circuits above at its differential input terminal, and outputs the difference voltage between the two outputs. A photometric device characterized by comprising a differential amplifier.