JPH07105663B2 - Amplifier - Google Patents

Description

The present invention relates to a device for amplifying an output voltage from, for example, a split photometric sensor of a single-lens reflex camera or the like.

[Conventional technology]

In recent years, a large number of single-lens reflex cameras and the like that use a split photometric sensor as a light-receiving sensor have been found.
The reason for using this split photometric sensor is that by dividing the viewfinder screen into a plurality of areas and independently performing photometry, the brightness in each zone can be measured, and fine exposure control can be performed. For this reason, the number of divisions of recent split photometric sensors tends to increase. However, if the number of divisions increases, the number of amplifiers corresponding to the sensor, and eventually the number of wiring lines to be connected, also increases, which causes a problem that noise easily occurs. Therefore, a so-called split photometric IC has been proposed in which an amplifier circuit, a control circuit, and the like are integrated inside the split photometric sensor. According to such a split photometric IC, the output is taken out in the form of voltage,
After being amplified by an inverting amplifier, it was A / D converted and input to a microcomputer for processing.

The output voltage of the split photometric IC is affected by the temperature characteristics of the logarithmic compression diode connected to the light receiving element. Therefore, conventionally, as the resistors connected to the inverting amplifier, a positive temperature coefficient resistor (positor) is provided on the input side and a metal film resistor, for example, is provided on the feedback side, whereby the temperature coefficient of the output of the inverting amplifier is set to zero. .

[Problems to be Solved by the Invention]

In the configuration in which the light receiving element is incorporated in the IC as described above, the gain of the inverting amplifier is determined by the ratio of the resistance of the metal film resistance to the resistance value of the posistor, and when the gain is adjusted, the posistor is expensive. There is no choice but to change the resistance value of the resistor. However, in order to make the resistance value of the metal film resistance variable, it is necessary to provide a large number of resistances. That is, a large number of elements must be connected to the outside of the IC that constitutes the inverting amplifier, which causes a problem that the configuration of the entire device becomes complicated.

The present invention has a simple structure, and A /
It is an object of the present invention to provide an amplifying device which can obtain a gain matching a D converter and can also be used as a temperature measuring device.

[Means for solving problems]

A voltage generation circuit whose output voltage has a predetermined temperature characteristic, a reference voltage generation source which outputs a predetermined reference voltage, an operational amplifier which amplifies the difference between the output voltage and the reference voltage, and which is connected to the output side of this operational amplifier, A resistor having a temperature characteristic opposite to that of the output voltage, a gain setting means connected to the input side of the operational amplifier and having a variable resistance value, a positive-phase input terminal, a negative-phase input terminal of the operational amplifier, and a voltage generation circuit. And a reference voltage generating source are electrically connected to each other to provide a resistance of a predetermined magnitude on the input side of the operational amplifier.

〔Example〕

 The present invention will be described below with reference to illustrated embodiments.

FIG. 2 shows an example of the configuration of an optical system. A mirror 12 is provided behind the taking lens 11, and a focusing plate 13 and a pentaprism 14 are provided above the mirror 12. Shooting lens 11
The light that has passed through is reflected by the mirror 12 and the pentaprism 14 and sent to the photometric sensor 15 and the eyepiece 16. In front of the photometric sensor 15, the image on the focus plate 13
A lens 17 for forming an image on the light receiving surface of is provided.

FIG. 3 shows a photographing screen 21 in the finder, and in the photographing screen 21, a first photometric range 22 and a second photometric range 23 are formed. In the present embodiment, the first photometric range 22 has a rectangular shape, and the second photometric range 23 is located in the center of this rectangular shape and has a circular shape. As shown in FIG. 4, the light receiving element provided in the photometric sensor 15 includes a first light receiving surface 24 corresponding to the first photometric range 22 and a second light receiving surface 24 corresponding to the second photometric range 23.
And a light-receiving surface 25 of the light-receiving surface 24, and the light-receiving surfaces 24 and 25 are separated from each other. That is, in this embodiment, the light receiving element is divided into two, and the photometric sensor 15 is a so-called two-division photometric IC.

FIG. 1 shows a photometric circuit 30 provided in the photometric sensor 15,
The structure of the amplifier circuit 40 is shown. The amplifier circuit 40 is provided in the same temperature environment as the photometric circuit 30, and the output voltage V
_{The LOG} is amplified with temperature compensation and output to an A / D converter (not shown).

In the photometric circuit 30, the light receiving element 32 is connected to each input terminal of the operational amplifier 31, and the diodes 33 and 34 are connected to the input and output terminals of the operational amplifier 31. That is, the operational amplifier 31 and the diodes 33 and 34 form a logarithmic compression circuit, and the detection signal of the light receiving element 32 is output as a logarithmically compressed voltage V ₀ . The diode 34 is a diode for clamping the output voltage V ₀ . On the other hand operational amplifier
The output terminal of the operational amplifier 31 and the constant current source 36 are connected to each input terminal of the amplifier 35, and the diode 37 is connected to the input and output terminals of the operational amplifier 35. That is, the operational amplifier 35 and the diode 37 form a level shift circuit.

In this embodiment, the photometric sensor 15 is a two-division photometric sensor as described above, and includes an operational amplifier 31 and diodes 33, 34.
The logarithmic compression circuit consisting of
Individually provided. These two logarithmic compression circuits are selected by being controlled by a control signal from a CPU (not shown), and one logarithmic compression circuit output is connected to the amplifier circuit 40. Note that only one logarithmic compression circuit is shown in FIG.

Now, assuming that the reference voltage supplied to the positive-phase input terminal of the operational amplifier 31 is V _S1 and the voltage acting on the diode 33 is V ₃₃ ,
The output voltage V ₀ of the operational amplifier 31 is Is. Where K is Boltzmann's constant, T is absolute temperature,
q is a constant, the current in I _P the diode 33, i ₀ is a constant value of current flowing through the diode 33, V (i ₀₎ is the voltage value when the current i ₀ flows through the diode. Further, the voltage V _LOG output from the photometric circuit 30, a voltage acting on the diode 37 when the V _37, And substituting equation (1) into this, Becomes

That is, the output voltage V _LOG of the photometric circuit 30 takes a positive value with reference to V _S1 as shown in FIG. 5, and the closer the light amount detected by the light receiving element 32 is (I _{P is} large), the closer to V _S1 . In FIG. 5, the reference voltage V _S1 is set to 2V.

Further, as understood from the equation (2), the output voltage V _LOG from the photometric circuit 30 is affected by the temperature change. This output voltage V _LOG is input to the amplifier circuit 40 in order to eliminate the influence of this temperature and to amplify the output voltage V _LOG with a gain matched with the A / D converter.

As will be described later, a positive temperature characteristic resistor and a gain setting circuit capable of changing the resistance value by opening and closing an analog switch are connected to the operational amplifier 41 in the amplifier circuit 40, and this gain setting circuit has a plurality of resistors. Have.
In the following description, the symbol shown in parentheses after the phrase "resistance" indicates the resistance value.

Now, the positive-phase input terminal of the operational amplifier 41 has two resistors (R ₁
/ 2) to the photometric circuit 30 and the negative-phase input terminal is connected to the voltage source that outputs the reference voltage V _S1 via the resistor (R ₁ ). The positive-phase input terminal of the operational amplifier 41 is connected to resistors (R ₀ , R, 2R, 4R, 8R) connected in series with each other, and the resistor (8R) is connected to the positive-phase input terminal of the operational amplifier 42 described later. It is connected to a voltage source that outputs the reference voltage V _REF . Similarly, the negative-phase input terminal of the operational amplifier 41 is connected to resistors (R ₀ , R, 2R, 4R, 8R) connected in series with each other, and the resistor (8R) is connected to the output terminal of the operational amplifier 41. . Analog switches SW1 to SW4 are connected to the resistors (R, 2R, 4R, 8R) on the positive phase input terminal side, and analog switches SW5 to SW8 are connected to the resistors (R, 2R, 4R, 8R) on the negative phase input terminal side. Are connected. These analog switches SW1 to SW8 are CPU
ON / OFF control is performed by a control signal from, thereby controlling the connection relationship of the resistors (R, 2R, 4R, 8R) and adjusting the gain of the operational amplifier 41, that is, the amplifier.

The output terminal of the operational amplifier 41, resistor having a positive temperature characteristic (R ₃₎ is connected, the resistor (R ₃₎ is connected to a negative-phase input terminal of the operational amplifier 42. With this resistor (R ₃ ), temperature correction is performed on the output voltage from the operational amplifier 41, and the temperature coefficient of this output voltage becomes zero.

The reference voltage V _REF is supplied to the positive-phase input terminal of the operational amplifier 42. This operational amplifier 42 is connected to an A / D converter (not shown) via a transistor 43, and the transistor 43 and A
A resistor (R ₄ ) is connected to the / D converter. The output voltage of the operational amplifier 41 is level-shifted and amplified by a predetermined gain by a circuit including the operational amplifier 42, the transistor 43, and the resistors (R ₃ , R ₄ ).

With the above configuration, the amplifier circuit 40 can amplify the output voltage of the photometric circuit 30 and perform temperature correction. Further, the amplifier circuit 40 has a function as a temperature measuring device in addition to the amplifying and temperature compensating functions, and a configuration therefor will be described next.

That is, while the resistor connected to the input terminal of the operational amplifier 41 and (R _1/2) and a resistor (R ₁₎ is connected via the analog switch SW9, also the resistance to the positive phase input terminal of the operational amplifier 41 (8R ) Is connected via an analog switch SW10 and a resistor (R ₅ ). These analog switches SW9 and SW10 are in a non-conducting state when the amplifying circuit 40 acts as a normal amplifier, but are set in a conducting state when the amplifying circuit 40 acts as a temperature measuring device. ON / OFF control of the analog switches SW9 and SW10 is performed by the CPU.

Next, the operation when the amplifier circuit 40 acts as an amplifier will be described.

In this case, the analog switches SW9 and SW10 are open, and a predetermined one of the analog switches SW1 to SW8 is closed. Note that the analog switches SW1 and S
W5 is always opened or closed at the same time, and similarly, the analog switches SW2 and SW6, SW3 and SW7, and SW4 and SW8 are ON-OFF controlled in pairs.

FIG. 6 shows an equivalent circuit when the amplifier circuit 40 acts as an amplifier. In this figure, a resistance (R ₂ ) is a combined resistance value of resistances (R, 2R, 4R, 8R) determined by ON-OFF control of analog switches SW1 to SW8,
It is the sum of the resistance (R ₀ ). First, the output voltage R _T1 of the operational amplifier 41 is obtained.

V _S1 + (R _T1 -V _S1 ) R ₁ / (R ₁ + R ₂ ) = V _LOG + (V _REF -V _LOG ) R ₁ / (R ₁ + R ₂ ) Therefore, R _T1 = V _REF + (R ₂ / R ₁ ) (V _LOG −V _S1 ). Substituting equation (2) into this, Therefore, the output voltage R _OUT of the amplifier circuit 40 is Becomes

Here, R ₁ and R ₂ are diffusion resistances in the IC and have the same temperature coefficient, and I _P and I _CC have the same temperature coefficient. The resistance (R ₃ ) has a positive temperature coefficient, and the temperature coefficient of the resistance (R ₄ ) is 0.
Is. Therefore, the temperature coefficient of the output voltage R _OUT is Becomes R ₁ and R ₂ have the same temperature coefficient with each other, and
Since I _P and I _CC have the same temperature coefficient,
(ΔR ₂ / ΔR ₁ ) and (ΔI _CC / ΔI _P ) are constants. Therefore, the temperature coefficient of the output voltage R _OUT is a constant C
When written using Becomes

Therefore, if R ₃ and T have the same temperature coefficient, that is,
If the temperature coefficient of resistance (R ₃ ) is + 3333ppm / ° C (corresponding to 301/300), (ΔT / ΔR ₃ ) becomes constant and the output voltage
The temperature coefficient of R _OUT becomes zero. That is, by selecting the resistor (R ₃ ) having such temperature characteristics, the output value of the amplifier circuit 40 is not affected by the temperature.

Next, the gain of the amplifier circuit 40 will be described.

Here, assuming an 8-bit A / D converter and its resolution is 4000 mV / 255 = 15.686 mV / step, G = 15.686 mV / (17.79 / 8) mV = 7.053 is required as gain G. is there. However, 17.79mV is the output voltage change amount of V _LOG when the brightness changes by 1 Ev, that is, (17.79 /
8) mV corresponds to 1/8 Ev value. In this embodiment, the operational amplifier 41 in the preceding stage has a gain of about 2.35 times, and the operational amplifier 42 in the subsequent stage has a gain of about 3 times. However, considering the error of resistance value and the variation of resolution based on the variation of reference voltage in A / D conversion, the gain of the operational amplifier 41 in the previous stage is set to ON-OFF of analog switches SW1 to SW8.
It is configured to be programmable and changeable by control. That is, the gain in this operational amplifier 41
PG is PG = (225 + 2 × Gain Code) / 100 (times), and Gain Code is input from CPU and takes a value of 0-15. Therefore, the gain range can be changed between PG = 2.25 and 2.55 (times) and at intervals of 0.02 times (2/100).

As described above, the amplification circuit 40 can also be used as a temperature measuring device. FIG. 7 shows an equivalent circuit of the amplifier circuit 40, that is, the temperature measuring circuit when the analog switches SW9 and SW10 are closed. In this case, the size of the resistance (R ₂ ) is the sum of the combined resistance of the resistances (R, 2R, 4R, 8R) and the resistance (R ₀ ) determined by the ON-OFF control of the analog switches SW1 to SW8. , R ₂ = R ₀ + {composite resistance value of (R, 2R, 4R, 8R)}.

First, the value of R _T1 is calculated.

_{V S1 + (R T1 -V S1} ) R 1 / (R 1 + R 2) = V S1 + (V REF -V S1) (R 1/2) / (R 1/2 + R 2 // 5) Accordingly, However, R _{2 // 5} = R ₂ · R ₅ / (R ₂ + R ₅ ).

Since R ₁ , R ₂ , and R ₅ are resistors in the IC, and V _REF and V _S1 are reference voltages, the temperature coefficient of each is 0, and thus R _T1 has no temperature coefficient.

The output voltage R _out of the amplifier circuit 40 is Becomes

Since R ₃ has a positive temperature characteristic here, R _OUT has a negative temperature coefficient. Therefore, the amplifier circuit 40 outputs the voltage R _OUT according to the temperature.
Is used as a temperature measuring device.

Here, for example, R ₁ = 100 kΩ, R ₂ = 235 kΩ, R ₃ = 5.1 kΩ, R ₄
= 15kΩ and R ₅ = 100kΩ, equation (5) and (6)
From the equation, R _T1 = 4.788 (V) R _OUT = 2.318 (V), and the temperature coefficient of R _OUT is Becomes Therefore, in the case of an 8-bit A / D converter, the resolution is 1 LSB = 15.686 mV. Therefore, according to the temperature measuring device of this embodiment, a temperature change of 2 ° C changes the A / D conversion value by 1 LSB. Will be done.

As described above, the amplifier circuit 40 of the present embodiment can be used not only as an ordinary amplifier but also as a temperature measuring device. When used as a measuring device, they are different from each other and therefore need to be adjusted in advance. Therefore, the data for this adjustment
Must be stored in the RAM of the CPU. For this reason, one means is to add an E ² PROM as an external device to the microcomputer, write the adjustment data to the E ² PROM in advance during the adjustment stage, and then read the specified data from the E ² PROM during actual operation and store it in RAM. A method of storing it is possible.

As described above, the amplifying device of this embodiment basically has only the resistance (R ₃ ) and the resistance (R ₄ ) as external parts, and the other parts are built in the IC. Therefore, the temperature compensation and the predetermined gain setting can be secured at the same time without using a large number of external parts as in the conventional case, and the entire apparatus can be simplified and the cost can be reduced.

〔The invention's effect〕

As described above, the amplification device of the present invention, while maintaining the temperature compensation, can obtain the gain matched with the A / D converter, and the configuration is very simple because there are few external parts,
The effect is produced. The amplification device of the present invention can also be used as a temperature measuring device.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an amplifier device according to an embodiment of the present invention, FIG. 2 is a diagram showing a configuration example of an optical system of a camera, FIG. 3 is a diagram showing a photometric range in a finder, and FIG. FIG. 5 is a diagram showing a light receiving element, FIG. 5 is a graph showing a change in output voltage of the photometric sensor with respect to an Ev value, FIG. 6 is a circuit diagram showing an amplifier, and FIG. 7 is a circuit diagram showing a temperature measuring device. 30 …… Metering circuit 40 …… Amplifying circuit R ₃ …… Positive temperature characteristic resistance

Claims (1)

[Claims] 1. A voltage generating circuit whose output voltage has a predetermined temperature characteristic, a reference voltage generating source which outputs a predetermined reference voltage, an operational amplifier which amplifies a difference between the output voltage and the reference voltage, and an output of this operational amplifier. A resistor having a temperature characteristic opposite to that of the output voltage, a gain setting means connected to the input side of the operational amplifier and having a variable resistance value, and a positive phase input terminal of the operational amplifier and a negative phase input. An amplifying device comprising: a terminal, a voltage generating circuit, and a reference voltage generating source, which are electrically connected to each other to apply a resistance of a predetermined magnitude to the input side of the operational amplifier.