JPS60168110A - Automatic focus detecting device - Google Patents

Abstract

PURPOSE:To reduce a circuit scale and to reduce a cost by inputting one optical output of a photodetector and an output which has switched the other output as a time series, to a differential amplifier, respectively. CONSTITUTION:A reflected light from a closest focusing distance is made incident on a photodetecting part 18a of a semiconductor position detecting element 18, and a counter 5 stops its operation. As it becomes a long distance, the reflected light moves to a photodetecting part 18d, a signal output of a differential amplifier 19 moves to a plus side, an output of the counter 5 becomes ''1'', and a light emitting diode 16b for indicating a distance of an object to be photographed emits a light. In case of a short distance, the reflected light is made incident on a photodetecting part 18b, therefore, the signal output of the differential amplifier 19 moves to a minus side, the counter 5 stops its operation, a lens is focused to a distance of an object to be photographed corresponding to an output 1 of the counter 5 by a lens controlling circuit 14. In case when the reflected light is between the middle of the photodetecting part 18b and 18c, and 18d, in case when the detection is difficult, the lens is focused in accordance with an output 4 of the counter 5. In this way, a resolution of the number of output terminals of the position detecting element 18 can be realized by a simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus detection apparatus, and more particularly to an automatic focus detection apparatus using a semiconductor device detection element as a light receiving element thereof.

Conventionally, this type of automatic focus detection device amplifies the signals from two output terminals of the light receiving element, and divides the difference between the amplified signal outputs by the sum to estimate the spot position on the light receiving element. , converted to distance. Therefore, two lines of processing circuits such as amplifier circuits are required, resulting in a large circuit size, which poses a major problem in terms of space and cost when built into a camera.

The present invention has been made in view of the above problems, and its purpose is to reduce the circuit scale and cost by using only one series of processing circuits such as amplifier circuits. The purpose of this invention is to provide an automatic focus detection device that can perform the following tasks.

In the present invention, an arbitrary one output among a plurality of outputs of a light receiving element and an output obtained by switching the other outputs in time series are respectively input to a differential amplifier, and a series of amplifiers and a processing circuit are used to select the light receiving element. The feature is that the upper spot position is detected, and automatic focus detection is possible with a very simple processing circuit, making it possible to obtain extremely high effectiveness. ' Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing the principle of the automatic focus detection device according to the present invention. 1 is a light emitting element such as an infrared light emitting diode, 2A is a projecting lens, and the light beam of the 1 light emitting element is directed onto a subject 6A. It has a convergence function, and 4A is a light receiving lens that focuses on the subject 6.
It functions to form an image of the light emitting element on A onto a light receiving element 5A, and 5A is a light receiving element, which is composed of a semiconductor device detection element,
There are three or more output terminals (in this figure, 5 a r5
b, 5c, 5d).

In operation, one light emitting element starts emitting intermittent light at a predetermined frequency in conjunction with a photographing preparation operation (not shown). Next, any one output among the outputs of the light receiving element 5A (for example,
5a) and other outputs (5b.

5c, 5d) are sequentially switched in time series.
The distance to the subject is detected from the connection state of the output terminal at the time when it crosses a predetermined value.

FIG. 2 is a circuit diagram of one embodiment of the present invention.

The specific operation of this embodiment will be described below with reference to FIG.

1 is a power battery, and 2 is a circuit power switch, which is turned on by slightly pressing the shutter button. When the power switch 2 is turned on, power is supplied to the entire circuit, and at the same time, the potential (Va) at point a rises instantaneously due to the differentiating circuit composed of the capacitor 6 and the resistor 4, and the counter 5 and the flip・Flop 6 is reset, and as a result, counter 5 (output is 85) outputs 0,
The output (S6) of flip-flop B becomes low level.

In addition, the oscillator 7) has a predetermined frequency (for example, 10
The oscillation signal is applied to a transistor 8 for driving a light emitting element and a synchronous detection circuit 9. This causes the light emitting element 10 to emit light at a predetermined period (in this case, 10
KHz) repeatedly turn ON and OFF S! The incoming synchronous detection circuit 9 outputs a signal (S9) synchronized with the blinking cycle of the light emitting element 10. This synchronous detection circuit 9 has conventionally been widely used in automatic focus detection devices, and its explanation will be omitted here.

The frequency of the oscillation from the oscillator 7 is divided by a frequency divider, and the frequency becomes, for example, 10 Hz, which is applied to one input of the ant game and 11. The output S6 of the flip-flop B is inverted by the inverter 12 and added to the other side of the AND gate 11. are added at the same time.

In this embodiment, the decoder 13 is operated by three people and has five outputs.

Initially, since the output S5 of the counter 5 is 0, the output of the 0 terminal of the decoder 16 (813) is at high level, and the other four terminals are all at low level. In this state, the transistor 15a is turned on and the light emitting diode (LED) 16a emits light. Five light emitting diodes 16a to 16e are LEs for displaying object distance.
In D, 16a indicates the closest distance, successively further distances are displayed, and 16e indicates infinity. For example, it is applied as a zone mark display in the viewfinder to indicate the distance to the subject. At this time, the field effect transistor (pET) 1.7a is also turned on. The source terminal side of the four FETs 17a to 17d is connected to the output terminal of a semiconductor device locking element 18, which is shown surrounded by a dashed line. In FIG. 2, this semiconductor device detecting element 18 is schematically shown as aqua regia, and includes four photodiodes 18a to 18.18 with one electrode in common. The other electrodes of i are shown as being connected to each other via a resistor, but in reality the photodiodes are connected in series.

Furthermore, although the conventional semiconductor device detection element has two output terminals, the present invention employs these two plus an intermediate output terminal. That is, in this embodiment, as shown in FIG. 2, the output is taken out from five terminals.

As described above, since only the FET 17a is initially ON, the outputs from both ends of the semiconductor device detection element 18 are taken out and applied to both input terminals of the differential amplifier 19. After the DC component of the output of the differential amplifier 19 is removed by a capacitor 20, it is input to the above-mentioned synchronous detection circuit 9, and as a result, the signal component of the light emitting diode 10 is extracted and converted to DC.
It is input to the inverting input terminal of the comparator 21. on the other hand,
A predetermined reference voltage (in this embodiment, a level slightly lower than the output from the synchronous detection circuit 9 when the reflected light from the object does not enter the semiconductor device detection element 18) is applied to the non-inverting input terminal of the comparator 21. ) is manually set.

For example, let's consider a case where the subject is at close range. At this time, the reflected light from the object enters the light receiving section 18a of the semiconductor device detection element 18, and from that point the FET 17
The output current on the a side increases, and as a result, the comparator 21 (output is 821) outputs a high level,
The output (S6) of flip-flop A is inverted, and the counter 5 stops operating.

Next, as the object becomes further away, the reflected light from the object moves toward the light receiving section 18a of the semiconductor device detection element 18, the output current of the FET 17C increases, and the signal output of the differential amplifier 19 increases. The level of moves to the positive side,
The output S9 of the synchronous detection circuit 9 also moves to the positive side, and since the output S21 of the comparator 21 is at a low level, the counter 5 starts operating. Then, after a predetermined period of time,
The output of the counter 5 becomes 1, the 0 output of the decoder 16 becomes a low level, and the 1 output becomes a high level. That is, the transistor 15a is 0FF17.
At the same time, the transistor 15b is turned on and the light emitting diode 16b emits light. Also, FET17C is OFF
Therefore, 17b is turned ON.

At this time, if the subject is relatively close, the reflected light from the subject enters the light receiving section 18b of the semiconductor device detection element 18, so the output current flowing through the FET 17b is
More signal current (221 in this example) flows than the fixed output terminal on the 18d side, the signal output of the differential amplifier 19 moves to the negative side, and the output S9 of the synchronous detection circuit 9 also moves to the negative side. The output 821 of the comparator 21 is inverted from low level to high level, the output S6 of the flip-flop B becomes high level through the OR gate 22, the output of the inverter 12 becomes low level, and the counter 5 operates. stop.

By further pressing the shutter button in this state, the photographing lens begins to move, and the lens control circuit 14 adjusts the subject distance to correspond to output 1 (S5) of the counter 5.
Adjust the focus of the shooting lens.

In addition, if the subject distance is far and the reflected light from the subject is closer to the 18d side than the center of the light receiving sections 18b and 18e, the output S21 of the comparator 21 will be at a low level and S6 will also be at a low level, as described above. Then, the counter 5 starts operating. After a predetermined period of time in this state,
The output of counter 5 becomes 2, and the output of decoder 16 also becomes 2.
only will be at a high level. In this case, light emitting diode 1
Only FET 6c emits light, and only FET 17C is turned on.

Same as above (=, the reflected light from the subject is transmitted from between the light receiving parts 18b and 180 of the semiconductor device detection element 18 to 18c
If the incident occurs during this period, the output of the comparator 21 (
S21) becomes high level, and the counter 5 stops operating.

When light enters from the light receiving section 18c to the f318d side, as described above, the output of the comparator 21 (S20 remains at low level. When a predetermined period of time elapses in this state, the output of the counter 5 becomes 3, Also, only output 3 of the decoder 16 becomes high level.

Similarly to the above, the light emitting diode 16d emits light, and the FET
17d is turned ON. Similarly, when the reflected light from the subject enters from the light receiving section 18c to a point midway between 18c and 18d, the output (S2+) of the comparator 21 is inverted and the counter 5 stops operating.

If light enters between the light receiving sections 18c and 18'd and 18'd, or if the reflected light is weak, the counter 5 advances by one after a predetermined time in the same manner as described above. , and the output of the decoder 16 also becomes high level. At this time, the light emitting diode 16e emits light, and at the same time a high level signal is sent to one input terminal of the OR gate 22, and the counter 5 unconditionally stops operating regardless of the level of the other input signal of the OR gate 22. .

That is, the reflected light from the subject is transmitted to the light receiving sections 18b and 18.
When the distance is between the middle of c and 18d, or when the reflected light from the subject is so weak that it is difficult to detect, the photographing lens is focused on the subject distance corresponding to output 4 of the kakunta 5.

Further, in this embodiment, the semiconductor device detection element has five terminals, but this is not limited to five terminals, and it is easy for those skilled in the art to increase or decrease the number of terminals as necessary. That is clear.

Further, according to the present invention, a distance measuring device having a resolution corresponding to the number of output terminals of a semiconductor device detection element can be realized with a very simple configuration. This is because the level difference between any two outputs from the semiconductor device detection element is detected in the first stage, so only one series of analog processing circuits is required. In addition, A/D for lens control
This is because since the conversion is performed using a semiconductor device detection element, A/D conversion can be performed without providing any special additional circuit.

As explained above, the present invention has the advantage of reducing the circuit scale and reducing costs.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of an automatic focus detection device according to the present invention, and FIG. 2 is a circuit diagram of an embodiment of the present invention. 1A...Light emitting element, 2A...Light projection lens. 6A...Subject, 4A...Light receiving lens. 5A... Light receiving element. 5a, 5b, 5c, 5a---output terminal. 18...Semiconductor device detection element. 19... Differential amplifier, 21... Comparator. Agent Tadashi Wakabayashi

Claims (1)

[Claims] A semiconductor device detection element having at least one output terminal at both ends and an intermediate thereof, a signal from one end of the output terminal is inputted to one input terminal, and a signal from the other end is inputted to the other input terminal in chronological order. What is claimed is: 1. An automatic focus detection device comprising: a differential amplifier that receives a signal and a signal from an intermediate output terminal, and detects a subject distance from the state of the output.