JPH01143910A - Automatic distance measuring instrument - Google Patents

Abstract

PURPOSE:To amplify a photocurrent excellently even when the photocurrent varies greatly and to perform accurate distance measuring operation by the amplification by detecting reflected light from a body to be measured by a photoelectric conversion element. CONSTITUTION:The photoelectric conversion element which is a semiconductor position detecting device (PSD) 1 detects the reflected light from the body to be measured. The output current of this PSD 1 is supplied to a logarithmic compressing circuit 15, whose output is supplied to an arithmetic circuit 16 and a voltage comparing circuit 17 in common. This circuit 17 is supplied with the output reference voltage of a reference voltage generating circuit 18 and compares it with the output voltage of the circuit 15 to outputs a voltage corresponding to their difference. Then when the measuring operation is not performed, a switch circuit 19 is on, the output of the PSD 1 is a photocurrent irrelevant to the distance measuring operation, and the output voltage of the circuit 15 is held constant. When the measuring operation is performed, on the other hand, the circuit 19 turns off and a photocurrent based upon the reflected light from the body to be measured flows together with the constant photocurrent irrelevant to the distance measuring operation and the circuit 16 performs proper arithmetic operation for those outputs, thereby finding the distance to the object body.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an automatic distance measuring device, and in particular, in an autofocus system such as a still camera, a photocurrent signal from a charging conversion element such as a semiconductor device detection device (PSD) is used. The present invention relates to an automatic distance measuring device for determining the distance to a subject.

BACKGROUND OF THE INVENTION FIG. 5 shows a circuit diagram of an autofocus system to which a conventional automatic distance measuring device is applied.

In the figure, 1 is a semiconductor device detector (hereinafter abbreviated as PSD), and a light emitting diode (LED) D to be described later.
This is a well-known semiconductor element that catches the reflected infrared light emitted from L toward the subject, converts it into photocurrent, and outputs it from terminals 1a and 1b. The above reflected light j is PS
Since it changes depending on the distance between Dl and the object to be measured, the output photocurrent of PSDl corresponds to the distance to the object.

2 is a charging current amplification circuit that amplifies the photocurrent obtained by the PSDl and prevents a large photocurrent from flowing due to external light such as sunlight, and 3 is the output terminal 1a of the PSDI.
This is an arithmetic circuit that logarithmically compresses the amplified photocurrents outputted from , lb, respectively, and calculates the difference between these values.

4 is the output of the arithmetic circuit 3 (a focal point that calculates the distance to the subject from g and supplies a control signal to the drive unit 5 that changes the focal length of the lens so that the lens can focus on the subject) 6 is a control circuit, and 6 is a light emitting unit that supplies current to a light emitting diode (LED) D1 just before the shutter is released, and emits infrared light from the light emitting diode D1 toward the subject.

7 controls the sequence of the circuit by transmitting and receiving signals for the start of autofocus operation, the start and end of distance measurement operation, and the end of autofocus operation with a control unit (not shown) that controls the entire autofocus system. This is a sequence control circuit that performs

The operation of the photocurrent amplification circuit 2 will be briefly described above.

The bias circuit 10 applies appropriate bias to current-voltage converters 11.12 and operational amplifiers (hereinafter abbreviated as OP amplifiers) 13.14, and the current-voltage converters ii, 12
The photocurrent signal generated at the output terminals 1a and 1b by Dl is converted into a voltage signal.

OP amplifier 15. Resistors R1, R2, R3゜PNP transistor Q1. NPN transistor Q2. Capacitor C1
A feedback loop (referred to as loop 1) and an OP amplifier 14. Resistor R4゜R5, R6, PNP transistor Q3
．． NPN+- transistor Q4. The feedback loop (referred to as loop 2) consisting of the capacitor C2 is connected to the ○P amplifier 13.
(If the input voltage of ゜14 is affected by external light unrelated to distance measurement operation such as sunlight, the output current of PSDI increases), to prevent the output from becoming saturated and not operating linearly with respect to the input. This is the circuit.

Since loop 1 and loop 2 have similar configurations, the operation of only loop 1 will be explained.

When the input signal voltage level supplied to the inverting input terminal of the OP amplifier 13 rises and the output signal voltage of the OP amplifier 13 rises to a predetermined level or higher, the PNP transistor Q1 turns on, and subsequently the NPN transistor Q1 turns on. Q2 is turned on. For this reason, OP amplifier 10
The DC voltage supplied to the inverting input terminal of the OP amplifier 10 flows as the collector current of the NPN transistor Q2.
An increase in the output voltage above the predetermined level is suppressed.

Problem to be Solved by the Invention The photocurrent that flows through the PSDl when infrared light reflected from the object is detected by the PSDl is different from the object at the closest distance where distance measuring operation is possible and at an infinite distance. Even if the reflectance of the subject is the same, it will be about 102 times more polished, and even if the subject is at the same distance, the reflectance will be different when the reflectance is small, such as when the subject color is black, and when the reflectance is small, such as when the subject is white. Even if the reflectance is high, the polishing tool will be about 102 times as large. Therefore, the size of the polishing tool will be about 104 times that of the case where the photocurrent is the smallest and the case where the photocurrent is the largest.

In the conventional circuit, there is a problem in that it is very difficult to select the constants of each element constituting loop 1 and loop 2 under conditions that are satisfactory in all cases when the amount of current differs greatly.

Further, there is a problem in that the bias current supplied from the bias circuit 10 to the OP amplifiers 13 and 14 imparts a bias to the photocurrent, which causes an error in the distance measuring operation.

The present invention has been made in view of the above points, and can effectively amplify the photocurrent even when the photocurrent flowing through the photoelectric conversion element changes significantly by detecting the reflected light from the object to be measured. It is an object of the present invention to provide an automatic distance measuring device that can perform accurate distance measuring operations.

Means for Solving the Problems The present invention detects reflected light from an object to be measured using a photoelectric conversion element that converts incident light into a photocurrent, and performs calculations on the output photocurrent of the photoelectric conversion element. In an automatic distance measuring device that measures the distance to a measuring object, a predetermined constant current is passed through the nonlinear circuit that generates an output signal according to the photocurrent supplied from the photoelectric conversion element, and when not measuring. and current control means for controlling the input photocurrent of the nonlinear circuit, and controlling the input photocurrent so that a predetermined constant current and a photocurrent due to reflected light from the object to be measured flow through the nonlinear circuit during measurement. .

When the action is not being measured, even if the photocurrent changes in response to changes in the brightness of external light such as sunlight, a predetermined constant current flows through the nonlinear circuit by the current control means, and the jlFA type circuit maintains a predetermined constant current. operation at the operating point is possible.

During measurement, in addition to the same predetermined constant current as immediately before the start of the measurement operation, a photocurrent due to reflected light from a wide range of objects under test flows through the nonlinear circuit, and the nonlinear circuit generates an output signal according to the photocurrent due to this reflected light. occurs.

The output signal of the nonlinear circuit is subjected to calculation in the next stage calculation circuit, etc., and the distance to the object to be measured is determined from the result.

Example FIG. 1 shows a block diagram of a first embodiment of the invention.

In the same figure, PSDl is PS in the conventional circuit of FIG.
It is similar to Dl and is a photoelectric conversion element that converts reflected light from an object to be measured into photocurrent. This photocurrent includes light emitted from the device itself for ranging operation, reflected by the subject and converted into photocurrent by the PSDl, and
It also includes photocurrents generated by extraneous light, such as sunlight and indoor lighting, that are unrelated to distance measurement operations.

This psoi output current is supplied to a logarithmic compression circuit 15, and these outputs are commonly supplied to a fraud circuit 16 and a voltage comparison circuit 17. At the same time, the output reference voltage of the reference voltage generation circuit 18 is supplied to the voltage comparison circuit 17, which is compared with the output voltage of the logarithmic compression circuit 15, and outputs a voltage according to the difference.

The output of the voltage comparison circuit 17 is supplied to the current bypass circuit 20 via the switch circuit 19 and charges the capacitor C.
The current supplied from PSDI to the logarithmic compression circuit 15 is bypassed in accordance with the output from 7. This switch circuit 19
is turned off by an operation to measure the distance to the object to be measured.

When the switch circuit 19 is on, the light used for the 1-distance operation is not emitted, and the output current of the psoi is caused by external light unrelated to the distance measurement operation, such as sunlight or indoor lighting. This is the photocurrent generated.

This photocurrent is converted into a predetermined voltage in a logarithmic compression circuit 15, and the output voltage is supplied to a voltage comparison circuit 17 and compared with a reference voltage generated by a reference voltage ff- generation circuit 18.

Here, if the output voltage of the logarithmic compression circuit 15 exceeds the reference voltage, the voltage comparison circuit 17 amplifies and outputs the voltage corresponding to this difference, and supplies the amplified voltage to the current bypass circuit 20. The current bypass circuit 20 lowers the output voltage of the logarithmic compression circuit 15 by bypassing a part of the photocurrent supplied from the PSDI to the logarithmic compression circuit 15 using the output of the voltage comparison circuit 17, and as a result, the output voltage becomes equal to the reference voltage. Become.

Conversely, when the output voltage of the logarithmic compression circuit 15 falls below the reference voltage, the current bypass circuit 20 reduces the bypassing of the current from the PSDl and increases the current supplied to the logarithmic compression circuit 15. As a result, the output voltage of the logarithmic compression circuit 15 increases. As a result, the output voltage of the logarithmic compression circuit 15 is always kept constant.

When the distance measurement operation is started, infrared light for distance measurement is emitted toward the object to be measured, and in synchronization with this, the switch means 19 is turned off. The infrared light reflected from the object to be measured is detected by the PSDl and converted into a photocurrent, but the current bypass circuit 2
0 continues to bypass the same current as that just before the switch circuit 19 was turned off by the voltage supplied by the capacitor +jC that had been charged up until then. Therefore, the photocurrent corresponding to the infrared light emitted for the distance measuring operation passes through the logarithmic compression circuit 15, is converted into a logarithmically proportional voltage, and is supplied to the arithmetic circuit 16. The arithmetic circuit 16 performs appropriate operations on this logarithmically converted voltage signal to determine the distance to the object to be measured, and performs a focusing U operation of the lens.

FIG. 2 shows a circuit diagram of a second embodiment of the invention.

In this figure, the same components as in FIG. 1 are denoted by the same reference numerals, and their explanations will be omitted. In this embodiment, as in the conventional example shown in FIG. 5, the photocurrent from the PSDI flows from the output terminals 1a and 1b to two circuits, and in FIG. They are distinguished by a and b. Since both are similar in operation, only the one indicated by the subscript a will be explained.

The photocurrent generated at the terminal 1a of PSDI is transmitted through the logarithmic compression circuit 15.
The logarithmic compression circuit 15a supplied to the input side is a well-known analog circuit configured by a transistor Q5 and an OP amplifier OP1, and outputs a voltage obtained by logarithmically converting the current supplied to the input side.

When the switch circuit 25a constituted by a semiconductor element is turned on by a signal supplied to the terminal 26a, the OP amplifier OP2 serving as a voltage comparison circuit is generated by the logarithmic compression circuit 15a and the reference voltage generation circuit 18. The voltage is compared with a reference voltage, and the difference is amplified and supplied to the current bypass circuit 20a, and the capacitor Ca is charged.

The current bypass circuit 20a is constituted by five transistors, and the output signal 3 of the OP amplifier OP2 is supplied via the switch circuit 25a, so that the OP amplifier OP
The photocurrent supplied to the inverting input terminal of 1 can be controlled.

When the switch circuits 25a and 25b are both on, no infrared light for distance measurement is emitted, and a photocurrent IDC generated by external light such as sunlight is generated in the PSDI. At this time, the second
Current flowing from psoi to terminals 1a and 1b shown in the figure 1.
I4 has the following relationship: 1 = I = I, o(1).

If the output voltage of the logarithmic compression circuit 15a is to fluctuate for some reason, this fluctuation will cause the output voltage of the OP amplifier OP2 to change when the OP amplifier OP2 compares the output voltages of the logarithmic compression circuit 15a and the reference voltage generation circuit 18. As the current I2 that changes and is bypassed by the bypass circuit 20a also changes, the current I3 flowing to the inverting input terminal of the OP amplifier oP1 increases or decreases so as to keep the output voltage constant. Therefore, the output voltage of the logarithmic compression circuit 15a (same as 15b) is balanced to be equal to the reference voltage supplied from the reference voltage generation circuit 18.

At this time, the photocurrent 1.15 bypassed by the current bypass circuits 20a and 20b is 12 = 11 + 13, respectively.
-■fi (2115=I4+■6
There is a relationship called IF5 ■. Here I
3. I6 indicates the current flowing to the inverting input terminals of the OP amplifiers ○p and op3, respectively, and 1f1. If2 is the transistor Q5. Q
This is the current flowing through 6. Here, O
P amplifier OP and O20 and OP amplifier 0P and o
When manufactured so that the characteristics of P4 are the same, l3=16, thereby forming the bypass circuit 20a.

The current 1.15 bypassed by 20b is 1 −
15, so I fl"" I I2
The relationship (4) holds true.

Therefore, at this time, the output voltage e1 of the OP amplifier OP1 and O
The output voltage e3 of the P amplifier OP3 is equal to the output voltage e3 according to a well-known formula. However, here k is Boltzmann's constant, ■
is the absolute temperature, q is the electronic charge, and Is is the temperature of the transistor Q5. This is the saturation current of Q6.

Therefore, the output voltage e5 of the first stage OP amplifier OP5 of the arithmetic circuit 16 is as follows. This equation means that when the switch circuits 25a and 25b are on, the output of the arithmetic circuit 16 is zero regardless of the strength of external light such as sunlight.

Next, the switch circuits 25a and 25b are terminals 26a.

When turned off by the signals provided to 26b, respectively,
In synchronization with this, infrared light is emitted toward the subject from an LED (not shown) serving as a light emitting means. When this infrared light is reflected by the object and detected by the PSDl, a photocurrent of 1
．． 1 will flow. PSDl depends on the reflectance of the subject, but in general, when the subject is far away, the reflected light is small, so both photocurrents 1 and I are small; on the other hand, when the subject is close, the reflected light is large, so the photocurrent is small. 1.14 both become larger. Furthermore, as the distance to the subject increases, the ratio of the light tli current 11°14 increases to 1.
, and conversely, as the distance to the subject approaches, the ratio of photocurrent I to I4 increases.

Immediately after the switch circuits 25a, 25b are turned off at the same time, the potential on the input side of the bypass circuits 20a, 20b is changed to the level immediately before the switch circuits 25b, 25b are turned off due to the charges stored in the capacitors C, , Cb. Bypass circuit 20a because they are equal.

The voltages 11 and 15 bypassed by 20b are also equal to those immediately before switch circuits 25a and 25b are turned off,
Therefore, the output voltage e1. of the OP amplifier OP1°OR3. e
3, both switch circuits 25a and 25b for a while.
is the same as before it was turned off.

Here, the photocurrent II due to the reflected light from the object is
When flows in a pulsed manner, the photocurrents flowing through terminals 1a and 1ba-3b are '1-'DC+' Sa
(7) 14=I,. +ISb ■. At this time, similarly to the 0 type, the output voltage e1. e3 are respectively, and therefore the output voltage e5 of the OP amplifier OP5 is as follows. At this time, the subject is close enough and I,1 (Is
a, 1f2(Isb), then (1
1) Equation is as follows, and the output of P amplifier OP5 is proportional to the logarithm of the ratio of photocurrent 1 and I due to the reflected light from the subject.
sb voltage will appear.

The OP amplifier OP7 is a well-known peak hold circuit that temporarily holds the peak value of the output voltage of the OP amplifier OP5, and performs accurate distance measurement even when the reflected light from the subject appears only for a short time. It is for tightening.

Further, in FIG. 2, 22 is a focal length control circuit that divides the distance to the subject into 8 stages according to the magnitude of the output signal of the calculation unit 16, and makes this correspond to the focal length of the lens in 8 stages. is a sequence control circuit which operates in the same way as the sequence control circuit in the conventional circuit shown in FIG.

FIG. 3 shows a timing diagram of the main signals of the circuit of FIG. In the same figure, Vcc switches the power supply to the entire circuit (no. n), and the power is turned on when it becomes high level at time t1. 30 is turned off and preparations are made for data capture.
The time of 25 milliseconds from 1 to t2 is set as a waiting time until the entire circuit becomes stable.

At time t2, the switch circuit 30 is turned off, and at the same time, the signal indicated by B becomes high level, and the light emitting diode emits light for 0.8 milliseconds until time t5. During this period, the switch circuits 25a, 25b, and 31 simultaneously
17, and from time t3 0.1 milliseconds after t2 to t
When the signal C becomes high level for 0.3 milliseconds up to 4, photocurrent due to reflected light from the object is detected.

When the light emission from the light emitting diode ends at time t5, the signal becomes high level, indicating that the distance measuring operation has ended.

FIG. 4 shows photocurrent 'sa' plotted on a logarithmic scale. It is a characteristic diagram showing the output voltage e5 of the P amplifier oP5 using the ratio of the photocurrent ■sa to Isb as a parameter. (1
As can be seen from equation 1), a current I, 1° 1.2 (from equation (4), I f1 = 1 f2) flows through transistors Q5 and Q6 to ensure operation, so the photocurrent '
When both sa and Isb are small, the approximation expressed by equation (12) no longer holds true, and as the photocurrent ■sa becomes smaller, the influence of Ifl becomes stronger, and the value of e5 gradually decreases as shown in Figure 4. , photocurrent ■sa, Isb. In particular, the ratio of Isa to Isb r 1 (= I , / 1
This tendency becomes more pronounced as sb) becomes larger and the subject becomes closer, and conversely, when r 1 = 1 (when the subject is at infinity), the line always becomes a constant straight line.

However, in the situation where distance measurement is actually performed by detecting the reflected light from the subject, if the subject is far away and the reflected light from the subject is small, rI is also small, mainly in area A in Figure 4. Distance measurement is performed based on the characteristics of the area, and when the subject is nearby, rI increases, but the total amount of light reflected from the subject also increases and the photocurrent Isa also increases, so mainly the A distance measurement operation will be performed based on the characteristics of the region entrance. The characteristics of both regions A and [i can be considered as almost horizontal straight line portions, and since the characteristics of such straight line portions are used, there is almost no problem with the resolution and error during distance measurement.

In the circuit shown in Fig. 2, the photocurrent from the PSDl is directly converted into a logarithmic voltage in the logarithmic compression units 15a and 15b, so unlike the conventional device, the current at the end of the tip is converted into a voltage signal, amplified, and then logarithmic compression is performed. It is possible to obtain a wider dynamic range compared to the case where this method is used.

In addition, OP amplifier OP1. Since the bias current flowing through OR3 is also treated as part of the photocurrent due to external light, it is possible to reduce the error in distance measurement operation caused by this bias 74'e+.

Effects of the Invention As described above, according to the present invention, it is possible to widen the dynamic range, thereby increasing the photocurrent range to 10
It is possible to perform good operation over a wide range of about 4 times as much as the polishing tool, and it is also possible to improve the resolution of distance measurement operation, and the photocurrent due to external light such as sunlight ), so if a small photocurrent caused by signal light such as infrared rays flows through this transistor, it is possible to achieve high resolution. It becomes possible to increase the switching from about 3 stages to about 8 stages with the same scale circuit configuration.

Furthermore, since the bias current of the OP amplifier that constitutes the logarithmic compression circuit is processed in the same way as the photocurrent due to external light,
It has the advantage that the bias current does not affect the photocurrent caused by the minute signal light, making it possible to perform highly accurate ranging operations.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of the present invention, FIG. 2 is a circuit diagram of a second embodiment of the present invention, FIG. 3 is a timing chart of the circuit shown in FIG. 2, and FIG. 2 is a diagram showing the operating characteristics of the circuit shown in FIG. 2, and FIG. 5 is a circuit diagram of a conventional device. 1... Semiconductor device detector (PSD), 15... Logarithmic compression circuit, 16... Arithmetic circuit, 17... Voltage comparison circuit, 18 ・MWl, 'li pressure generation time' M, 19.25
a, 25b...Switch circuit, 2o...Current bypass circuit, ○P1-OP4...Operation amplifier circuit (OP amplifier), c, c, cb...Capacitor, Q5. Q6...
・Transistor. Patent applicant Mitsumi Nki Co., Ltd.

Claims (1)

[Claims] A photoelectric conversion element that converts incident light into a photocurrent detects reflected light from the object to be measured, and a calculation is performed on the output photocurrent of the photoelectric conversion element to detect the object to be measured. In an automatic distance measuring device that measures the distance of a non-linear circuit that generates an output signal according to the photocurrent supplied from the photoelectric conversion element, a predetermined constant current is caused to flow through the non-linear circuit when not measuring. current control means for controlling an input photocurrent of the nonlinear circuit, and controlling the input photocurrent so that the predetermined constant current and a photocurrent due to reflected light from the object to be measured flow through the nonlinear circuit during measurement; An automatic distance measuring device characterized by: