JPS6227614A - Light measuring circuit for distance detection - Google Patents

Abstract

PURPOSE:To make it possible to remove AC background light, by guiding out an output, which undergoes photoelectric conversion and current-voltage conversion, to a load for removing the AC background light at the next stage through a capacitor. CONSTITUTION:A first, before light is projected on an object, a constant output voltage is guided out of a load 13 for removing background light by the nonoperating state of a switching means 16. Therefore, the potential at one side of a capacitor 12 is always constant. Since one side of the capacitor 12 is at the potential of the constant voltage output, said side has low impedance. In the capacitor 12, the electric charge corresponding to the output of photoelectric conversion at that time point is stored without time delay. When the light is projected, the output of a constant voltage circuit 15 is cut off from the load 13 by the switching means 16 in synchronization with the light projection. The reflected light from the object, on which the light is projected, undergoes photoelectric conversion and current-voltage conversion. The voltage is transmitted to the load 13 through the capacitor 12, and the output of the load 13 is changed. At this time, the timing of the latching is synchronized with the timing of the light projection as close as possible. Therefore, the detected output of a distance, in which the effect of the AC background light is negligible, can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a photometric circuit for distance detection, specifically, a light beam is projected toward a subject from a light projection means, and the light reflected from the subject is received by a light receiving means. The present invention relates to a photometry circuit in a light projection type distance measuring device that measures distance by

[Prior Art] One of the technical problems that must be solved in a light projection type distance flPJ determination device is the problem of background light.

There are two types of background light: steady background light and alternating current background light. Regular background light is light that changes slowly over time due to sunlight, etc., and alternating current background light is light that changes slowly over time due to sunlight, etc., and alternating current background light is light that changes slowly over time due to sunlight, etc. This is light with twice the frequency of commercial AC power. The current generated by this background light in the light receiving element of the a-1 optical circuit is normally about several 1009 A due to reflected light, which is signal light, whereas the current generated by background light due to sunlight is about several 1.
AC background light from a 0 μA1 incandescent lamp or the like is about several tens of nA, which is much larger than the signal light, and distance measurement cannot be performed unless this is removed.

Therefore, various solutions have been proposed in the past, such as in Japanese Unexamined Patent Publication No. 54-121164, but all of these methods involve storing the background light component in a storage capacitor in advance (background light + signal light). ) - (background light) This is a method for extracting changes due to signal light by adopting a circuit configuration that provides (background light).

However, this method has the following three drawbacks.

(I) In this method, background light components (mainly stationary background light components such as sunlight) are memorized in advance and subtraction processing is performed, so it requires memory retention time to complete the memorization and subtraction processing. In order to save time, the capacity of the memory capacitor must be increased. The size of this capacitance is approximately on the order of μF, and a typical capacitor of this size is a tantalum capacitor. This tantalum capacitor costs about four times as much as a ceramic capacitor, leading to an increase in cost.

(n) This method attempts to find the size of the signal light by subtracting (background light + signal light) - (background light), but as mentioned above, the background light is 1000~
Since it is 10,000 times larger, unless complete subtraction processing is performed, the subtraction error of the background light component becomes a significant signal light component extraction error. In fact, cameras that use this photometry method produce distance measurement errors in high-brightness environments.

Furthermore, if the circuit is made more precise and a complete subtraction process is attempted, the circuit scale will increase, which in turn will lead to an increase in cost.

(If) If the storage capacitor is too large, it will no longer follow the AC background light, and as a result, an error will be included in the signal light component due to incomplete removal of the AC background light.

Therefore, the simplest method to eliminate the influence of background light is to derive the photoelectric conversion output from the photometer via a capacitor and to project light onto the subject in a pulsed manner. A method (see Japanese Patent Publication No. 48-19250) has been considered in which only the time-varying portion of light is extracted. According to this method, stationary background light components such as sunlight can be removed relatively easily and completely.

However, artificial light sources such as incandescent lamps have an alternating current component with a frequency twice the frequency of the driving power source.

This alternating current component is not cut by the capacitor and is transmitted to the next stage. Therefore, under a subject condition where AC background light exists, the signal light and the AC background light component are confused, resulting in erroneous distance measurement.

In other words, the background light removal method using capacitor coupling is either a very effective method in terms of cost removal rate for stationary background light, or it is very problematic in terms of removal rate for AC background light. . As a countermeasure to this problem, it is possible to construct an active filter by combining capacitor coupling and appropriate CR constants to detect only the frequency components of the signal light. The number of R and C increases several times, which poses a problem in terms of cost. Furthermore, since the frequency of the signal light and the frequency of the AC background light are not far apart, there is also a problem in terms of removal rate. Attempting to perform a sufficiently high modulated projection compared to the frequency of the AC background light in order to increase the rejection rate would result in an increase in cost and power consumption.

[Problems to be solved by the invention] The conventional method of removing background light by capacitor coupling is effective for stationary background light, but AC background light cannot be removed and may cause erroneous distance measurements. Become. As a countermeasure to this problem, it is effective to project modulated light at a sufficiently high frequency compared to the frequency of the AC background light and provide an active filter on the receiving side, but such a method would result in a complicated circuit configuration and increase costs. It becomes expensive and consumes a lot of power.

The present invention has been made in view of the above-mentioned problems, and it is possible to remove background light with a relatively simple circuit configuration that does not cause erroneous distance measurement even when AC background light is present. The purpose of the present invention is to provide a photometric circuit for detecting distance.

[Means for Solving the Problems] The photometric circuit of the present invention derives the photoelectrically converted and current-voltage converted output to a load for removing AC background light at the next stage via a capacitor, and also A constant voltage circuit whose output end is connected to the derivation point is installed to keep the potential at the point constant.
Further, there is a switching means for cutting off the output of the constant voltage circuit in synchronization with the time when the photometric pulse light is projected onto the subject, and a change in the output of the AC background light removal load is latched in conjunction with this switching means. The latch means is provided.

[Function] First, before light is emitted toward the subject, the load for removing background light outputs a constant voltage with the switching means inactive, and this causes the potential on one side of the capacitor to decrease. is always constant, and since one side of this capacitor has a constant voltage output potential, it has a low impedance, so that the capacitor accumulates charge corresponding to the photoelectric conversion output at that time without time delay.

When light is emitted next time, the switching means cuts off the output of the constant voltage circuit from the load in synchronization with it. The reflected light from the subject due to the projection of light is photoelectrically converted, current-voltage converted, and transmitted to the load via the capacitor, causing an output change in the load. At this time, the latch timing is synchronized with the light projection timing as much as possible, thereby obtaining a distance detection output in which the influence of AC background light can be almost ignored.

[Example] First, before explaining the present invention in detail, the distance measuring principle of the two-point distance detection circuit used in the present invention will be explained with reference to FIG. The light projecting means includes a light projecting light source using a light emitting diode 1 such as an IRLED, a projecting lens 2, and a light source drive circuit 3, whereby a light beam is projected onto the subject 4 in a pulsed manner. Then, the reflected light from the subject 4 is focused by the light receiving lens 5, and the light is collected by the light receiving element 6.
It is photometered by The light-receiving element δ is set in advance at a position where it receives reflected light closer than a certain distance, based on the well-known distance a1 constant principle of triangulation.

Therefore, by detecting the presence or absence of reflected light, it is possible to recognize whether the subject 4 is closer than a certain set distance or on the side.

With this configuration, the Al photoelectrically converted by the light receiving element 6
1j optical output is converted into current-voltage by a detection circuit 7, and the output of the detection circuit 7 controls the extension of the photographing lens of the camera. The above is the distance measurement principle of the two-point distance detection circuit.

Next, the first part of the photometric circuit having the background light removal function of the present invention will be described.
An embodiment will be explained with reference to FIG. A11J light receiving element 8. The output terminal of a current-voltage conversion circuit 11 constituted by a photoelectric conversion circuit including an operational amplifier 9 and a feedback resistor 10 is connected via a capacitor 12 to one end of a load 13 for removing background light.

This load 13 is composed of a resistor in this embodiment, and a reference voltage V ref' is applied to the other end. The output end of a constant voltage circuit 15 made up of an operational amplifier 14 is connected to a connection point P between the capacitor 12 and the load 13. A reference voltage V ref is applied to one input terminal of the operational amplifier 14, and the other input terminal is connected to the connection point P, that is, the output terminal of the operational amplifier 14. Therefore, since the operational amplifier 14 is normally in a state where negative feedback is applied and the output end has zero impedance, the potential at the connection point P is maintained at the reference voltage V ref'.

The operational amplifier I4 forming the constant voltage circuit 15 is operated by applying the operating voltage Vcc when the switching transistor 16 is turned on, and becomes inactive when the transistor 16 is turned off. Output to the connection point P is cut off.

On the other hand, the connection point P is connected to one input terminal of the comparator 17, and the other input terminal has a voltage of 71 V rcr
The output terminal of the comparator 17 to which is applied is connected to a latch circuit 18. The output of the latch circuit 18 is then led out to a control circuit 19 of the photographing lens. On the other hand, a switch 20 is provided which is closed by the operator during distance measurement, and a resistor 21 is connected in series with this operation switch 20, and an operating voltage VCC is applied thereto. The connection point between the switch 20 and the resistor 21 is connected to a switching circuit 22 and a light source drive circuit 24 that causes the light emitting diode 23 to emit light, and when the switch 20 is closed, both circuits 2
2.24 can be operated at the same time. When the switching circuit 22 operates, it turns off the switching transistor 16 through the resistor 25 and at the same time sends a latch signal to the latch circuit 18.

In the photometry circuit of the first embodiment configured in this way, the light receiving probe 8 normally receives the background light and the signal light which is the reflected light of the subject, and the current-voltage conversion circuit 11 corresponds to this. Outputs a voltage signal.

Of this voltage signal, only the time-varying portion is connected to the capacitor 12.
is transmitted to the next stage. That is, at this time, the only currents transmitted are those due to the AC background light and the signal light, and the DC background light component, which is the steady background light, is transferred to the capacitor 12.
completely cut by. Further, the current transmitted through the capacitor 12 is absorbed by the output of the constant voltage circuit 15 constituted by the operational amplifier 14 and does not flow into the load 13. Therefore, the connection point P between the capacitor 12 and the load 13 is always kept at a constant potential even in the presence of AC background light.

When distance measurement is to be performed next, the operation switch 20 is closed by the operator. When this is closed, a high-level voltage signal is generated at the connection point with the resistor 21, so this high-level voltage signal operates the drive circuit 24, causing the light emitting diode 23 to emit light and emit a pulsed beam toward the subject. Project light. Further, in synchronization with this, the switching circuit 22 turns off the switching transistor 16, so that the application of the operating voltage to the operational amplifier 14, that is, the power supply is cut off, and the output of the constant voltage circuit 15 is cut off.

Since the operational amplifier 14 is configured so that both its input and output are in a high impedance Hz state when the power is turned off, all the current transmitted through the capacitor 12 now passes through the load 13.

Then, the potential at the connection point P fluctuates by more than the reference potential Vre. That is, as shown in FIG. The output of the photoelectric conversion circuit 11 that has received the reflected light varies as V. This variation is compared with the reference potential V ref by the comparator 17, and the comparison and output is output to the latch circuit 18. This latch circuit Since the latch timing pulse has already been supplied to 18 from the switching circuit 22, the output of the comparator 17 is latched by the pulse.The output of the latch circuit 18 is then supplied to the control circuit of the photographing lens, and based on this, the output of the comparator 17 is latched. Autofocus operation is performed by controlling the amount of lens extension.

Next, FIGS. 3 and 4 show a second embodiment of the present invention, in which FIG. 3 is an electric circuit diagram of a photometric circuit for distance detection, and FIG.
The figure is a time chart showing the operation.

In FIG. 3, the photometric light receiving element 28. operational amplifier 29
A current-voltage conversion circuit 31 constituted by a photoelectric conversion circuit including a feedback resistor 30 and a feedback resistor 30 outputs a voltage signal corresponding to the brightness of light measured by the light receiving element 28 . The voltage value output here is the photocurrent Ip generated, and the feedback resistor 30
Let Rf be the resistance value of Rf, and assume that a reference voltage of 0.6V is applied by two series-connected rectifiers 34 and constant current source 35, then (1,2+I pXRf)V and null.

The above output is applied via a capacitor 32 to the base of a transistor 33 constituting a load corresponding to the AC background light removal load 13 (see FIG. 1).

A bias current Il of an appropriate level is passed through this transistor 33 by a constant current source 36, and furthermore, a constant voltage is supplied to the base of an operational amplifier formed by connecting transistors 37.3g and 39°40 as shown in the figure. Output terminal P of circuit 41. is connected. The output of the constant voltage circuit 41 is of a follower type in which the base of the transistor 37, which is one input terminal of the operational amplifier, is connected to the collector of the transistor, so that feedback is applied to one input terminal. And the transistor 38 which is the input terminal of the operational amplifier
A diode-connected transistor 42 is connected to the base of
is connected, and a constant current (2) is passed through it by a constant current source 43 to generate a reference voltage vref. Therefore, the potential of the output terminal Pa of the constant voltage circuit 41, that is, the base potential of the transistor 33, becomes the same voltage as VBE generated when the current I flows through the transistor 42 due to the operation of the operational amplifier. 42 has the same characteristics, and 12-11Xβ
(β is the amplification factor of the transistor 33), so the V of the transistor 33 is the same voltage as the vBE of the transistor 42, and the output IE of the operational amplifier flows into or out of the base of the transistor 33. is very small.

Assuming that there is AC background light here, the variation in light due to this AC background light causes current to flow in and out through the capacitor 32. All of the inflow and outflow components at this time are absorbed by the constant voltage circuit 41 consisting of transistors 37 to 40 configured as an operational amplifier, and as a result, no current flows into the base of the transistor 33 and no current flows out fE, and the collector current of the transistor 33 I does not change, so vBE
remains unchanged and remains constant.

On the other hand, a constant current 3 is supplied to the collector of the transistor 33 by a constant current source 44. Here, ■3 is the collector current ■ of the transistor 33.

Therefore, the collector potential is approximately at the Vcc level.

The constant voltage circuit 41 is supplied with an operating voltage by a switching transistor 45 which together with a transistor 46 constitutes a current mirror circuit, and the transistor 46 is supplied with an operating voltage by a transistor 48 and a transistor 47 which constitutes a current mirror circuit. are connected in series. A constant current is supplied to the transistor 48 from a constant current a'X 49, and a series circuit of an operation switch 50 and a resistor 51 is connected to both ends of the series circuit of the constant current source 49 and the transistor 48. ing. Further, the connection point between the operation switch 50 and the resistor 51 is connected to the input end of a one-shot multi-by break 52, and the output end of the multi-by break 52 is connected to each input end and the latch circuit. It is connected to the set end of the D-FF circuit 55. The first delay circuit 5
The output terminal of the second delay circuit 54 is configured to send a latch signal to the D-FF circuit 55, and the output terminal of the second delay circuit 54 is configured to apply a drive signal to the input terminal of the drive circuit 57 of the light emitting diode 56. and is connected to the base of a transistor 59 through a resistor 58. Transistor 59 has its emitter connected to said transistor 47.
The emitter and collector of the transistor 47 are connected to the base of the transistor 47, respectively, and the transistor 47 is turned on and off.
It serves to control the off operation. Also, the D-FF circuit 55
The data input terminal of is connected to the collector of the transistor 33, and the Q output is led out to the control circuit 60 of the photographic lens.

Next, the operation of the photometry circuit of the second embodiment configured as described above will be explained with reference to the timing chart of FIG. 4. During distance measurement, the operation switch 50 is closed. When this is closed, the potential a at the connection point with the resistor 51 is as shown in FIG.
It changes from L to H as shown in a). Then, using this positive edge as a trigger, the one-shot multi-by-break 52 generates a one-shot pulse b (see Fig. 4).
b)) is output. As a result, the D-FF circuit 55
is set, and its Q output f is H (see Figure 4(f)).
becomes. Next, the second delay circuit 54 outputs a one-shot pulse C (see FIG. 4C) delayed by the pulse width of the one-shot pulse b. This pulse C
is supplied to the drive circuit 57, and the drive circuit 57 causes the light emitting diode 56 of the IRLED to emit light in synchronization with this pulse, and at the same time causes the transistor 5 to emit light through the resistor 58.
9, transistor 59 is turned on, transistors 47 and 48 are turned off, and transistors 45 and 46 are turned off accordingly. Therefore, the transistors 37 to 40 that constitute the operational amplifier
The constant voltage circuit 41 is cut off and becomes inactive. Further, due to this operation, the operational amplifier does not operate during pulsed light emission, and the current flowing in or out through the capacitor 32 is controlled by the base current of the transistor 33. Therefore, all the current change components generated by the light projection pulse become the base current of the transistor 33, and are amplified by the current amplification factor β of the transistor 33. Then, when the increase in the collector current of the transistor 33 exceeds the constant current I3, the collector potential e becomes the fourth
As shown in figure (e), it falls to L level.

Next, a pulse d (see FIG. 4(d)) slightly delayed from the one-shot pulse C is generated from the first delay circuit 53. This positive edge triggers the D-FF circuit 55, and the current state of the D input e
is latched. Then, the photographing lens control circuit 60 controls the photographing lens to a predetermined position based on this latched state Q output f (see FIG. 4(f)), and completes the autofocus operation.

In this way, the present invention removes DC background light (stationary background light) by so-called capacitor coupling, and provides a constant voltage circuit, which is switched to remove AC background light. In the embodiment, switching is performed by cutting the bias current, but as is well known, the same effect can be obtained by using a constant voltage circuit having a switching element such as an FET on the output side. Further, although the above embodiment has been shown for simplicity with respect to only a two-point distance measuring device, it is of course applicable to a multi-point 4v1 distance measuring device.

[Effects of the Invention] According to the present invention, (1) Since it is necessary to pass only minute and relatively short-time pulsed light components, the capacitor used only needs to have a small capacity, and therefore the cost is lower than that of the conventional one. The cost can be reduced to less than 1/4 of that of conventional products.

(2) Since it is a capacitor-coupled system, stationary background light is completely removed, there is no distance measurement error under high brightness as in conventional systems, and the circuit configuration is simple.

(3) Since AC background light can also be removed by the switching effect of the constant voltage circuit, it is more resistant to AC background light than the conventional system, and the circuit configuration for this purpose is also simple.

Remarkable effects such as

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram of a photometric circuit for distance detection showing a first embodiment of the present invention, FIG. 2 is a diagram showing a distance detection signal, and FIG. 3 is a diagram showing a distance detection signal according to a second embodiment of the present invention. FIG. 4 is a time chart of the electric circuit shown in FIG. 3, and FIG. 5 is a diagram showing the principle of the two-point distance detection circuit. 8.28・・・・・・Photometry photodetector 11.31
...Current-voltage conversion circuit 12.32...
・Capacitor 13.33... Load 15.41... Constant voltage circuit 16.59... Switch means (switching transistor) 23.56... Light means (light emitting diode) 1 ward 2 % 4 ward (f) L-111 "-11" - 11111 5th ward Procedure hli Original (self-motivated) 1. Display of incident 1985 Patent Application No. 167196 2
, Title of invention Distance detection/llll+optical circuit 3
, Name of the person making the amendment (037) Separate sheet for the "Claims" column and "Detailed Description of the Invention" column of the Olympus Optical Industry Co., Ltd. specification (1) "Claims" of the specification has been amended as shown in the attached sheet. (2) “Together” written in the fifth line from the bottom of page 5 of the specification
will be changed to "according to". (3) Delete "For AC background light removal" written from the end of the third line to the fourth line on page 7. (4) ``For AC background light removal'' written in lines 9 to 10 on page 7 will be deleted. (5) ``For background light removal'' written in the 7th cutoff from the bottom of page 7 will be deleted. (6) ``For background light removal'' written from the end of line 15 to line 16 on page 9 will be deleted. ``2. Claims: A light projection means for projecting pulsed light toward a subject; a current-to-voltage conversion circuit for converting a photocurrent generated in a photometric light-receiving element comprising a photoelectric conversion element into a voltage signal; - A load coupled to the voltage conversion circuit by a capacitor, a constant voltage circuit connected to the connection point of this load and the above capacitor and keeping the same connection point at a constant potential, and the output of this constant voltage circuit to the subject. switch means that cuts off the photometric pulsed light almost synchronously at the time when the photometric pulsed light is projected, and transmits to the load only the output corresponding to the light reflected by the same pulsed light when the photometric pulsed light is emitted. A photometric circuit for distance detection, which is characterized by the following features:

Claims (1)

[Scope of Claims] A light projection means for projecting pulsed light toward a subject; a current-to-voltage conversion circuit for converting a photocurrent generated in a photometric light-receiving element comprising a photoelectric conversion element into a voltage signal; A load for background light removal coupled to the voltage conversion circuit by a capacitor, a constant voltage circuit connected to the connection point of this load for background light removal and the above capacitor, and normally keeping the connection point at a constant potential; switch means for cutting off the output of the constant voltage circuit almost synchronously at the time when the photometric pulse light is projected onto the subject; A photometric circuit for distance detection, characterized in that only a corresponding output is transmitted to the load.