JPS62191702A - Operation circuit - Google Patents

Abstract

PURPOSE:To obtain a simple operation circuit easy to adjust, by providing a position detecting element, a means for performing logarithmic scaling and a differential amplifier containing one set of transistors. CONSTITUTION:The detection currents I3, I4 outputted from a light receiving element for detecting a position are applied to the bases of NPN transistors TR1, TR2 through diodes D3, D4 for logarithmic scaling and follower amplifiers 4, 5. The collector of the transistor TR1 is connected to a power source +VCC and the collector of the transistor TR2 is connected to a power source +VCC through a resistor R8. The output led out to the collector of the transistor TR2 is applied to one input terminals of a plurality of comparators C5-C8 and voltage for comparison obtained by respectively dividing the line between the power source +VCC and a constant current source I6 by resistors R9-R12 is applied to the other input terminals of the comparators C5-C8 to be compared with the voltage applied to one input terminals to form a distance signal. By this method, a circuit can be constituted using a resistance value easy to control and the load for planning is reduced and the enhancement of operation accuracy can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an arithmetic circuit, and more particularly to an arithmetic circuit for an automatic focusing distance measuring circuit used in a camera.

Conventional technology> Recent cameras use PSD (Positive SD card) as a position detection element.
Automatic focusing circuits using a 5-sensitivity diord are becoming mainstream, but this method is an active type ranging method based on the principle of triangulation.

In other words, when photographing, an IRED (infrared light emitting diode) is instantaneously emitted to illuminate the subject with a highly directional lens, and the reflected light is placed at a location perpendicular to the optical axis by a certain baseline length from the IRED. The distance is measured by projecting the current onto the PSD using a lens, and detecting the ratio by utilizing the fact that the ratio of the output current flowing between the two electrodes of the PSD changes depending on the projection position.

In the above distance measurement method, the intensity of the reflected light changes depending on the reflectance of the subject, so it is necessary to detect the ratio value. To do this, first, obtain the voltage by logarithmically compressing each current, and then calculate the voltage. A distance signal is obtained by simultaneously comparing and discriminating the results using multiple comparators.

FIG. 2 shows a circuit conventionally used to create a distance signal from such two input signals.

L, D2 are IREDs taken out from each electrode of PSD.
This is the signal current of reflected light. The above signal currents II and I2 are
They flow into the logarithmic compression diodes Dt and D2, respectively, and the first. It is applied to the non-inverting input of the second operational amplifier 1.2. The reference voltage Vre is applied to the inverting input of the first operational amplifier 1.
A resistor R1 is connected to f+, and a resistor R2 is connected to the output.
is connected. Further, a resistor R3 is connected between the inverting input of the second operational amplifier 2 and the output of the first operational amplifier 1, and a resistor R4 is connected between the output and the inverting input of the second operational amplifier 2. The output of the second operational amplifier 2 is not applied to one input of the plurality of comparators C1 to Cn. A reference voltage for comparison according to the distance division is given to the other inputs of the comparators C1 to Cn.

In the above circuit, when input currents I+ and Iz are applied, the forward voltages of the diodes DI and D2 are as follows.

■! DI:VF(DI)=/tn/,.

D 2 : V F (D 2 ) = /g tnZ
.

Here, K is Boltzmann's constant and 1g is the electron charge.

T is the absolute temperature +Io is the reverse saturation current.

If the value of resistance this winter is Rr = R2 = R3 = R4,
The output Vout (OF2) of the second operational amplifier 2 is as follows.

Vout(OF2)=2(Vp(D2)−VF(DI)
)+Vref+=2 //g(tn(2/Io)-4n
(1 B.) ) 10 Vref 1=2/gtn (2 people,
) +Vr e f 1 −·− (1) From this, it can be seen that an output determined only by the ratio is obtained regardless of the absolute values of the signal currents It and I2.

Next, let us consider what value the ratio of the signal currents II and I2 takes depending on the distance.

In autofocus using the zone method, ``Even though the width of each zone is constant within each zone and the focus point is constant, the size of the maximum circle of confusion caused by the width of the zone is Ideally, they should be determined to be equal. In such a case, the first . Second. ....

When the n-th zone is selected, the difference in the amount of lens extension for each zone is close to a constant value, so for ease of design, it is customary to set the amount of lens extension to be constant for each zone.

If the focal length of the photographing lens is f+, the amount of extension na
The relationship between (n=1.2...) and the focus position is as follows.

Assuming that f I > n, a is approximated, the above becomes, for example, when f 1 = 40 points and a = 0.4 points, that is, from the infinite position, as the lens is extended by 0.4 steps, the distance increases to 4 m and 2 m. , 1.33m + 1m On the other hand, the imaging position (optical axis distance) is t, and the focal length of the imaging lens of the PSD is I2, it can be expressed as follows, with the imaging position at infinity as the origin.

Therefore, for example, f+ = 40rHR, I2 = 20mm+
a=0.4mm.

When the condition is L=40tan, the imaging position X has the following value.

If you set the optical system so that the image is centered at 4 m, it will be 0.2 mm from the center and 0.4 rr at 2 m.
rm, 0.6 at 1.333 m and 0.6 at Im.
When the focus position button is set to 8mm, the image formation position on the PSD is 0.2・n”mm.At this time, the PSD
The ratio of current 11:I2 extracted from the two electrodes is 1:1.4m at infinity and 1.2:1.2 at 0.8.2m.
4:0.6, 1+0.2n:1-0.2n
The ratio will be

When the ratio of the above currents II and I2 is set to 'I4-26mV and substituted into equation (1), the output vout (OP 2 )
is as follows depending on the value of n.

(1+0.2n) Vout(□p2)=26X2Xtn, y50.
2. )+Vrf3fln”1 21.08 (Carp) 10vref.

n = 2 44・06 (mV) +vre f+
n”3 72.09 (my) + Vref.

n”=4 114.26 (my) + Vr8
t.

Therefore, each comparator C1 to C4 in the circuit of FIG.
The comparison voltage of comparator C1 is 21.08 mV.

Comparator C2 is 44.06mV, comparator C3
is 72.09mV, :7 comparator C4 is 114.2
If the reference voltage Vref2 + reference voltage Vref39 dividing resistance value Rs T R6 + R7 is determined so that each of them is higher than the reference voltage Vreft by 6 mV, the comparator C1-C4 outputs are all low for the measured distance ■ ~ 4 m. , for 4 to 2 m, the comparator Ctdi'
For high〃, 2~1.33□, comparator C+, C
Comparator C for z 'high', 1.33~1m
+, C2, and C3 are high, and for distances below 1 m, comparators C1 to C4 are all high, allowing distance measurement.

<Problems to be Solved by the Invention> In the conventional distance measuring circuit described above, since calculation is performed based on the ratio of l and resistance, highly accurate resistance (R1 to R4) is required.

Z: The circuit is complicated because two OP amplifiers are required for calculation.

3. Since the difference in comparison voltage is uneven, the dividing resistors R5 to R7 must be set at intermediate values, making it difficult to improve accuracy.

4. If the optical system is misaligned, the ratio will also change, so precision is required for alignment of the optical system.

There were other drawbacks.

<Means for Solving the Problems> The present invention has been made for the purpose of eliminating the drawbacks of the above-mentioned conventional circuits and providing a simple and easily adjustable distance measuring arithmetic circuit.

For a PSD that detects reflected light from a subject, the PS
The two detected currents from D are logarithmically compressed using the logarithmic compression characteristics of each transistor or diode, and the two logarithmically compressed outputs each include a set of transistors directly or via a follower amplifier at the base. The signal is inputted to a dynamic amplifier circuit to form an arithmetic circuit, and the output of the differential amplifier circuit is applied to a plurality of comparison circuits provided according to the distance division to form a signal based on distance measurement.

<Operation> The signal currents from the PSD are input to the bases of the transistors, respectively, and the calculation results of the two detection currents are obtained as the output of the differential amplifier.

<Example> In Fig. 1, a light receiving element (PSD,
(not shown) output from two detection currents I3. I4
are applied to the logarithmic compression diodes D3+D4, respectively, and to the bases of the NPN transistors TRI and TR2 via the follower amplifier 4.5. Note that the logarithmic compression diode D3. The cathode side of D4 is the reference voltage V. It is connected to the.

The emitters of both transistors TR1 and TRz are commonly connected to a constant current source I5. The collector of the transistor TR+ is connected to the power supply +Voo, and the collector of the transistor TR2 is connected to the power supply +Voo through the resistor R8. Connected to 0. The output led to the collector of the transistor TR2 is given to each input terminal of one of the plurality of comparators c5 to CB. The other input terminals of the comparators C5 to C8 are connected to a dividing resistor R between the power supply +VCo and the constant current source 6.
Voltages for comparison obtained by dividing the input terminals 9 to Rl 2 are applied, and compared with the voltage level applied to the one input terminal, to form a distance signal.

In the circuit having the above configuration, the diode D3. As mentioned above, D4 is set to 1 + 0 by PSD as in the conventional circuit.
．． A detection current having a ratio of 2n a 1-0.2n is flowing. Therefore, both diodes D3. D4 voltage difference V
F can be expressed as follows.

Vp (D4)-Vp■3)"Kr/gtn (1-
0・shif+0.2n) Also, the collector current of transistor TRI is ■.

(TR1), the collector current of transistor TR2 is IC
(TR2), both transistors T Rt , T
R2 noise voltage V (TRI), VBE (TR2)
Regarding the CI amount relationship, EV8E(TR2)-V8E(TRI)=%tn(TJ(TR,)).

The voltage of the diode D3 is applied to the base of the transistor TRr via the holoamp 4, and the voltage of the diode D4 is also applied to the base of the transistor TR2, so in the end, "T/g" ((1- “296+o, 2n a=ni/g”
(1C(T"2(TRt)), rc<T2.(TR4,=1-0."%+0.2n).

At this point, work between the constant current workman 5 and the constant current workman 5. (TR2) 10I. (T
Since there is a relationship of &)=αa is, if we consider it as αjiku1,
The following relationship is obtained from the above equation.

Therefore, the power supply voltage is V. 0, comparator 1-0
．． The positive input of 2n becomes Re I·° 2 .

At this time, for example, l5=2・Is R9=R1O=R
If you choose Il = RIz = 0.2・R8, as in the conventional circuit, when the distance is from infinity to 4 m, all the comparator outputs are - low. From 4 m to 2 m, only comparator C5 is high, 2
~1.333m, comparator Cs, Cs is one high.''1.333~1m, comparators C5, C6, C7.
When the distance is 1 m or less, the comparator C8 is high, and the distance measurement results are obtained as the outputs of the comparators C5 to C8.

In the circuit with the above configuration, even if there is a slight deviation in the optical system, this will result in two output currents of 1-0.2n:1+
No shift is given to 0.2n. i.e. 1-0.2n
+K: Appears in the form of 1+0.2n-, so 1
-0.2n This can be expressed as 'R8.5-A+', so it can be adjusted by simply shifting p, for example, by changing the value of the resistor &.

<Effects of the Invention> According to the present invention, a °C circuit can be constructed using easily adjustable resistance values, the burden on design can be reduced, and calculation accuracy can also be improved. In addition, the overall circuit configuration becomes simpler, making it easier to integrate the circuit.
A highly practical arithmetic circuit can be obtained.

[Brief explanation of drawings]

FIG. 1 is a calculation circuit diagram for camera distance measurement according to an embodiment of the present invention, and FIG. 2 is a conventional distance measurement circuit diagram. I3. I4: PSD output current D3 + D4:
Logarithmic compression diode 4, 5: Follower amplifier TRI
. TRz: Transistor C5-C8: Comparator R8
-R12: Resistance I5+I5: Constant current source agent Patent attorney Takeshi Sugiyama (and 1 other person) Vcc Suso φmb> 1st cA

Claims (1)

[Claims] 1) A position detection element that detects the position of incident light based on a resistance value between electrodes; means for logarithmically compressing two detection currents of the detection element; and two logarithmically compressed currents. It is equipped with a differential amplifier including a pair of transistors whose outputs are applied directly to the base or via a follower amplifier, and the result of calculation of the output current of the detection element is taken out as the output of the differential amplifier. A calculation circuit for distance measurement.