JPH0448209A - Subject distance detecting device - Google Patents

Abstract

PURPOSE:To improve the distance measurement accuracy and to prevent a signal value from exceeding a dynamic range by stopping at least a 1st or 2nd integrating means from operating according to a 1st or 2nd comparing means. CONSTITUTION:The device is equipped with the 1st integrating means 30 which performs integrating operation corresponding to a 1st current value I1, the 2nd integrating means 31 which performs integrating operation corresponding to a 2nd current value I2, the 1st comparing means 35 and 2nd comparing means 36 which compare the output of the 1st integrating means 30 and the output of the 2nd integrating means 31 with reference voltage respectively, and an arithmetic means 34 which calculates a subject distance according to the ratio of the 1st current value I1 and 2nd current value I2. At least the 1st integrating means 30 or 2nd integrating means 31 is stopped from operating according to the 1st comparing means 35 or 2nd comparing means 36. Namely, random noises that a signal photocurrent for AF contains are canceled by performing integration plural times.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a subject distance detection device, specifically, a device for detecting a subject distance, which projects pulsed light such as infrared light onto a subject, and determines the subject distance based on the reflected light from the subject. The present invention relates to an active type object distance detection device that detects.

[Prior Art] Autofocus (hereinafter abbreviated as AF) devices applied to still cameras, video cameras, etc. can be roughly divided into two types. One is a passive method that uses the brightness distribution information of the subject, and the other has its own light emitting means.
This is a so-called active method that measures distance using the reflected light of the projected light signal. The active method, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 1-291111, has a simple structure and is inexpensive, so it is popular. Next, an example is shown in FIGS. 5 and 6.

Figure 5 is a block diagram showing the configuration of the main parts of the active AF left camera known inside the shell.The light emitted by the infrared light emitting diode IREDI is focused by the floodlight lens 2 and directed towards the subject 3. The reflected light is reflected by the light receiving lens 4.
A well-known position detection element (hereinafter referred to as
(abbreviated as PSD) 5. The photocurrents I and I2 are divided into the PSD 5 according to the imaging position, and the divided photocurrents I and I2 are supplied to the AF IC 6. This AF IC 6 pulse-drives the IREDI through the I RED driving transistor A, and also receives the photocurrent 11. from the PSD 5. Based on I2 (
The distance measurement data is supplied to the CPU 7.

On the other hand, exposure control (which converts the brightness of the subject into an electrical signal)
The light receiving element 8 for EE (hereinafter abbreviated as EE) is the IC 9 for EE.
In combination with this, proper exposure is controlled. Also, the above CPU
Reference numeral 7 is responsible for the entire sequence of the camera, and also performs operations such as shutter opening time and driving the focusing lens. The output of the CPU 7 drives a motor 11 which is a power source for the driver 0 to wind up the shutter, film, and advance the lens.

FIG. 6 is a block diagram showing the configuration of the AF IC 6. That is, the photocurrent 11°I2 from the PSD 5 is input to the low input impedance amplifiers 12 and 13, respectively.
Photocurrent 11. I. Based on stationary light (after separating the DC current component), it is amplified.

Then, each output is sent to the arithmetic circuit 15. The signals are respectively input to the adder circuit 16. The adder circuit 16 adds the photocurrents II and its output 11+12 is supplied to one input terminal of the comparator 1° 2 . The other input terminal of the comparator 18 receives the output Iref of the comparison signal generation circuit 17.
is supplied.

The output of the path IB and the comparison signal Irer are also supplied to a subtraction circuit 23, and the subtraction circuit 23 calculates a signal r-(11+I2)er corresponding to the intensity of reflected light for long-distance distance measurement. The output of the subtraction circuit 23 is input to the integration circuit 20 via the switch 22. Then, the output of the integrating circuit 20 is taken out as AF data. Note that, at the start of integration, a predetermined integration start voltage is applied to the integration circuit 20 by the reset circuit 21.

The switch 19 is controlled by the output of the comparator 18,
Switch 22 is controlled by the inverted output of comparator 18. Therefore, depending on the magnitude relationship between 11+I2 and Iref, the integrating circuit 20 performs an integral calculation based on either the output of the arithmetic circuit 15 or the output of the subtraction circuit 23.

Here, if I, +12 is larger than Iref, it can be determined that the subject is close and the S/N ratio of photocurrent It, I2 is good; conversely, if Il + I2 is smaller than Irer, the subject is far away. Therefore, it is determined that it is difficult to ensure the accuracy of the arithmetic circuit 15, and in this case, the switch 19 is turned off, the switch 22 is turned on, and the output I − of the subtraction circuit 23 is
(11+12)ref' is input to the integrating circuit 20.

Here, the operating principle of the infrared light projection type triangulation distance measuring method for measuring the object distance using the PSD 5 will be described. When the optical axis of the light-receiving lens 4 is aligned with the center line of the PSD 5 and this is set as the origin, the incident position of the reflected light is X, and the distance between the principal points of the light-emitting lens 2 and the light-receiving lens 4, that is, the base line length is 51 If the focal length of the light-receiving lens 4 is f, then the subject distance g is:
1)-s-f/x......It is given by (1).

11. Photocurrent generated in PSD 5 due to light reflected from the object by IREDI. Both I2 are proportional to the reflected light intensity, but the photocurrent ratio I1/I2 does not depend on the reflected light intensity and is determined only by the incident light position X.

If the total length of PSD5 is t, then 11/I2-(7+x)/(zx)
becomes. If we substitute equation (1) into the above equation, we get...
(2) Therefore, if the photocurrent ratio 11/I2 of the PSD 5 is found, the subject distance g is uniquely determined.

If the above equation (2) is modified, it becomes 1+2 t, and at short distances where the photocurrents I and 12 are sufficiently large, the distance information g can be determined with high accuracy from equation (3). That is, ...... (4) [Problem to be solved by the invention] By the way, in the above-mentioned conventional technical means, the magnitude of the reflected light decreases as the subject distance increases, and S/
Since the AF calculation becomes inaccurate due to the deterioration of the N ratio, there is a problem that the measurable range is limited to relatively short distances. Especially landscapes where no reflected light is returned.
For subjects that are said to be at an infinite distance, AF calculations are performed using only noise components in the circuit.
Since noise is generated randomly, there is a high possibility of erroneous distance measurement at long distances.

That is, as the distance increases, the photocurrent 11°■ of the PSD 5 becomes smaller and the noise component INl'■N2 increases relatively, so the above equation (4) needs to be rewritten as the following equation (5). be.

・・・・・・・・・(5) When formula (4) is the theoretical value, 1 obtained by formula (5)
The error Δ- of 7p is !・・・・・・・・・(6)

The above noise component ■Nl''N2 is random noise, but after performing the ratio operation called Δk as in equation (6) above, no matter how much you integrate it, it will not approach zero, but , before the above ratio calculation is performed, the more the random noise is integrated, the closer it gets to zero.

On the other hand, if we look at the magnitude of the signal currents such as the photocurrents I and I, for example, when trying to measure a distance from 60cm to 10m, the ratio of the photocurrents to be handled must be 1 to 277 times, which is a very large dynamic range. Therefore, if the IRED simply repeats the operation of emitting light and integrating the amount of received light, there is a possibility of overrange at short distances.

Moreover, viewed from the other side, this also means that unnecessary light emission and integral operation are performed.

An object of the present invention is to eliminate the above-mentioned defects in the conventional distance detection device, improve the distance measurement accuracy in a ratio calculation type distance measurement device, and prevent the signal value from exceeding the dynamic range and save power. The object of the present invention is to provide a subject distance detection device capable of detecting a subject distance.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a light projection unit that projects pulsed light toward a subject, and a light projector that receives reflected light of the pulsed light from the subject and adjusts the distance to the subject. In a subject distance detection device having a position detection element that outputs a first current value and a second current value at a proportion corresponding to the first current value, the first integrating means performs an integrating operation according to the first current value, and the second a second integrating means that performs an integrating operation according to the current value; a first comparing means and a second comparing means that respectively compare the output of the first integrating means and the output of the second integrating means with a reference voltage; calculation means for calculating a subject distance according to a ratio between a current value and a second current value; It is characterized in that the operation of the means is stopped.

[Operation] Before calculating the distance to the object using the current value output in response to the reflected light from the object, the current value is integrated to reduce noise, and the integrated value is used to perform a ratio calculation to calculate the distance. , when the integral value is detected and sufficient current for calculation is obtained, the light projecting means and the integral operation are terminated.

[Example] The present invention will be explained below with reference to illustrated embodiments.

FIG. 1 is a block diagram showing the configuration of a subject distance detection device showing the basic concept of the present invention. In this Figure 1, IRE
Dl, IRED driver IA, PSD5. Light projection lens 2
．． Light receiving lens 4. The CPU 7, amplifiers 12, 13, etc. are constructed in the same manner as the conventional ones shown in FIGS. 5 and 6.

Photocurrent output of the above PSD5 1. ．． I2 is converted to DC by constant light by an amplifier 12.13 with low input impedance.
The current components are separated and amplified respectively, and the first .
The first reference voltage Vref is set by the second integration circuit 30.31.
' Integrate each using l as a reference. Through this integral operation, the REDI emits light multiple times toward the subject, and the rung noise contained in the photocurrent II output after receiving the reflected light is canceled out each time, producing an integral effect. be done.

The photocurrent signal whose S/N has been improved by this integration is input to the ratio calculation circuit 34, and the same calculation as in equation (4) is performed.

Further, this integrated voltage is constantly monitored by comparators 35 and 36, and the integrating operation is prohibited when the integrated voltage reaches a sufficient level.

That is, the above 1. The output of the second integrating circuit 30.31 is transferred to the first comparator 35.31. It is input to the + side input terminal of the second comparator 36, and each comparator 35, 3
A second reference voltage vref2 is applied to one side input terminal of the 6, and when the integral input voltage is about to exceed the permissible level vref2, the output of the NOR circuit 39 to which the outputs of the comparators 35 and 36 are input becomes " Since the level becomes L# and the Nant gate 37 and inverter 38 are turned off, the integral signal INT is not output and the integral operation ends.

In addition, in this distance detection device, the IREDI after the integration is disabled is
Since the light emission of IRED is meaningless, the light emission of IRED is also prohibited at the same time as the integral operation, so that the integral signal I
The NT signal is also manually input to the IRED driver IA.

In the distance detection device configured as described above, for a subject at a short distance, the amount of signal light is sufficiently integrated even during one IREDI light emission, and an END signal is outputted via the inverter 14. In addition, since the amount of signal light reflected from a distant object is not sufficient, the number of flashes increases and random noise tends to increase, but the number of integrations also increases, so the farther the object is, the more noise is caused by integration. The canceling effect becomes more effective, and distance measurement in long-distance areas, which has conventionally been considered weak in active AF, can be performed with high precision.

When the END signal is output, the CPU 7 detects it, reads the calculation result of the ratio calculation circuit 34 via the output circuit 32, and calculates the distance.

FIG. 2 shows an embodiment of the distance detecting device of the present invention more specifically constructed in accordance with the basic concept of the present invention shown in FIG. 1s1 above. PSD in this example
5. The amplifiers 12, 13, comparators 35, 36, inverter 38, NOR gate 39, etc. have the same functions as those shown in FIG. 1 above.

In addition, two signals of photocurrent 1.1 generated by the PSD 5 are amplified and integrated, and a second reference voltage vre is
Since the circuit systems to be compared with f2 are formed in exactly the same way, only the circuit system for one photocurrent 11 will be described here.

When pointing a camera at a subject, the subject is generally constantly illuminated by sunlight or artificial lighting, so
In addition to the signal light, steady light from these lights is incident on the PSD 5, and the PSD 5 outputs a steady light current IO from these lights. In AF calculation, this steady photocurrent I
. It is necessary to remove only the signal photocurrent 11°I2 due to IREDI (see FIG. 1) and extract it.

Therefore, first, the operation for removing this steady photocurrent will be explained. This steady photocurrent l. Basically, the component of the steady photocurrent 1o does not change between the state in which the IRED is not emitting light and the state in which it is emitting light, so the difference between the signal photocurrents I,, I2 and the signal photocurrents I,, I2 is as follows: This is done by determining that there is.

Before the emission of IREDI, the steady-state photocurrent I. is amplifier 12 (1
3) due to the low input impedance and is attempted to be amplified by the transistor 40 (54) through which a constant current ITB is passed by the constant current source 41 (55), the current flowing through the compression diode 42 (56) increases. .

However, the compression diode 42 (56) is biased in advance with the constant current IDB of the constant current source 43 (58),
This voltage level is observed by the negative input of the hold amplifier 51 (65). On the other hand, hold amplifier 51
The + side input of (65) is a compression diode 4 biased by a constant current source 50 (64) that also flows a constant current ■DB.
9 (63). Therefore, the hold amplifier 51 (65) is connected to the compression diode 4.
2 Steady photocurrent in (56)! .

When a current based on the transistor 53 (
67) to control the collector current of the stationary photocurrent I. is not input to transistor 40 (54), and transistor 5
3 (67) works to discard to GND. In this way, the steady-state photocurrent I is removed by the base potential of the transistor 53 (67).

Next, when IREDI emits light and signal photocurrent 11 (I2) is output from PSD5, B
The cUT signal (bias cut signal) is output, the hold amplifier 51 (65) stops functioning, and the constant current source 43
(58) is also turned off. At this time, steady photocurrent! . The transistor 53 (67) controlled to remove
Since the base potential of is held by the hold capacitor 52 (66), the signal photocurrent I. (I2) is the steady photocurrent ■. The compression diode 42 (5
6).

This compression diode 42 (56) is the transistor 44
(57) constitutes a current mirror circuit, and the same transistor 44 (57) has an amplified signal photocurrent 1
1 (I2) flows as the collector current.

At this time, the BCUT signal is sent from the timing circuit 33 to the switches 45 (59) and 46 (
60), is applied to the constant current source 43 (58), so the switch 45 (59) applied via the inverter 47 (61) is turned off, and the switch 46 (60) applied directly is turned on. .

Therefore, the amplified signal optical current 1 is applied to the integrating capacitor 48 (62) connected to this switch 46 (60).
1 (I2) flows in and is integrated. This integrating capacitor 48 (62) is initialized by the reset circuit 68 before the I RED emits light, and the integration start voltage becomes vref'l.

In this way, each time IREDI emits light and the signal photocurrent 11 is input, the voltage VINT proportional to the signal photocurrent I is integrated into the integrating capacitor 48. Similarly, the integrating capacitor 62 receives a voltage vINT proportional to the signal photoelectric voltage. is being integrated. Then, this integrated voltage is input to the + side of the comparators 35 and 36, respectively, and either integrated voltage is input to the comparators 35 and 36.
6, the comparator 35 or 36 operates to stop the integration operation.

Next, this is converted into a current signal, and the ratio calculation circuit 34 performs a ratio calculation based on the above equation (3). This ratio calculation circuit 34 is constructed by connecting amplifiers 69, 80, diodes 70.78, transistors 71.7B, 74°77, resistors 72, 79, buffers 81.82, constant current source 76, etc. as shown in the figure. ing.

When a voltage proportional to the photocurrent 11 (I2) is applied across the resistor 72 (79) of the ratio calculation circuit 34, the photocurrent I, (I2) is applied to the transistor 71 (77).
A current proportional to I2) flows.

Here, this is simply a photocurrent! , (I2), but it is important that the current is a current whose noise is canceled out by the integrating capacitor 48 (62) and the S/N is increased.

Therefore, a current proportional to the photocurrent 11 flows through the compression diode 70 as well, and the diode 70 is compressed. This voltage signal is transferred to the buffer 81
is input to the base of transistor 73 via. Similarly, a voltage signal compressed by a compression diode 78 and having a current proportional to the photocurrent I2 is input to the base of the transistor 74 via a buffer 82.

Since this ratio calculation circuit 34 similarly amplifies the photocurrents If and I2, the current flowing through the compression diode 70 is
If the current flowing through the IQ' compression diode 78 is 120, the current flowing through the base of the transistor 73 and the constant current source 76 is ■φ, so Ia+Ib−Iφ ・−−
--------(11) holds, and the above (10) and (11)
From Eq.

In other words, the above formula (4) and the above Ia = Vz + VT-g - (8
)" Is holds true. However, Vref'3 is the reference voltage,
Ig is a current flowing through the transistor 74, and Ib is a current flowing through the transistor 73. As a result, the following formula is established, and distance information g can be obtained depending on the magnitude of Ia.

In this embodiment, the current 1a is transferred to the transistor 74.
It is converted into a voltage by the output resistor 75 (RoU-D) connected to the collector of the CPU 7 (see Figure 1).
A converter makes it easy to read. That is, from V -R◆Ia OUT 00... (14) The timing chart until obtaining this VoUT is shown in the third
As shown in FIG.

In Figure 3, the subject distance is close and the integral voltage vINT□ is 2.
This is a case where Vref2 is reached in the second light emission. In this case, since the amount of light is sufficient, the distance measurement result V can be obtained with good accuracy without relying on the noise canceling effect caused by multiple integrations. 8
．． is obtained.

The timing chart in Figure 14 shows that the subject distance is far and I
For example, even if the RED emits light 32 times, the integrated voltage vIN
TI" INT2 does not reach V and ef2. In this case, in this embodiment, in order to prevent distance measurement time from becoming unnecessarily long, limiter signal END2 (second
(see figure) is output when the IRED finishes emitting light 32 times to forcibly end the distance measuring operation.

Then, when the END signal is output to the OR gate 83,
The constant current source 76 is turned on and VoUT is output.

[Effects of the Invention] As described above, according to the present invention, the random noise contained in the AF signal photocurrent is canceled out by multiple integrations, so that it is possible to provide an extremely accurate object distance detection device. I can do it.

Further, in the present invention, since distance measurement with a sufficiently good S/N can be performed when the integrated voltage of the signal photocurrent reaches a certain level, the distance measurement operation is terminated at that point. Therefore,
In areas where a sufficient amount of signal light can be expected for a subject at a close distance, the time lag can be reduced, and in this respect it is easier to use than conventional distance measuring devices.At the same time, it is possible to reduce the dynamic range of the integrated voltage by integrating the signal light. Since it also performs the following steps, it does not require complicated functions such as an auto gain control circuit or an auto power control circuit, and has the remarkable effect of being easily realized in terms of circuitry.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the configuration of a subject distance detection device showing the basic concept of the present invention. FIG. 2 is an electric circuit diagram of the subject distance detection device showing a specific embodiment of the present invention. FIG. 4 is a timing chart for explaining the operation of the subject distance detection device shown in FIG. 2, FIG. 5 is a block diagram of the main parts of an active AF camera, and FIG. FIG. 2 is a block diagram showing the configuration of a subject distance detection device in a camera. 1...IRED (light emitting means) 3...
...Subject 5...PSD (position detection element) 30.
...First integrating circuit (first integrating means) 31...
...Second integrating circuit (second integrating means) V, V
...Reference voltage reft ref'2

Claims (1)

[Claims] (1) A light projection means for projecting pulsed light toward a subject;
In a subject distance detection device having a position detection element that receives the reflected light of the pulsed light from the subject and outputs a first current value and a second current value at a ratio according to the subject distance, the first current a first integrating means that performs an integral operation according to the current value; a second integrating means that performs an integral operation according to the second current value; and an output of the first integrating means and an output of the second integrating means, respectively, as a reference voltage. a first comparison means and a second comparison means for comparison; and a calculation means for calculating a subject distance according to the ratio of the first current value and the second current value; A subject distance detecting device characterized in that the operation of at least the first integrating means and the second integrating means is stopped depending on the comparing means.