JPS5899709A - Signal light detecting circuit in distance measuring device - Google Patents

Abstract

PURPOSE:To avoid the occurrence of detection errors, by performing the sampling and detection corresponding to the period of background light. CONSTITUTION:When a first timing pulse is applied from a timing circuit 6a, a first switch 6b is turned On only for the width of said timing pulse. Based on this action, a first detecting circuit 6d performs the a sample and hold operation of a voltage corresponding to the level of the background light at this time. When the next timing pulse is generated by the timing circuit 6a after the specified time, a light beam irradiating means is started, and a second switch 6c is concurrently opened. As a result, the sample and hold operation of the voltage corresponding to the level of the sum of the background light and the signal light is performed by a second detecting circuit 6e. The outputs of the first and second detecting circuits 6d and 6e are compared in a comparing circuit 6f, and the signal light component is taken out.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal light detection circuit used in a distance measuring device used in an automatic focusing camera or the like.

2. Description of the Related Art Distance measuring devices that project an infrared beam onto a subject and detect the reflected light using a photodiode array to measure the distance to the subject are already in use.

When a subject is illuminated by an artificial light source, the level of brilliance of the subject changes. In the above device, it is necessary to detect changes in brightness when a subject is irradiated with an infrared beam or the like, distinguishing them from changes caused by light sources other than irradiation with the infrared beam.

Hereinafter, in this specification, light reaching a subject from a light source other than an infrared beam will be referred to as back shadow light. Is the subject irradiated with an infrared beam against the background light?
The light reflected from the signal is called signal light.

When a subject is illuminated with a fluorescent light or the like, the background light changes significantly, making it difficult to detect the signal light, so proposals have already been made to solve this problem. 1st
These proposals will be briefly explained with reference to the figures.

In FIG. 1, N1 indicates the level of back shadow light, which has relatively small fluctuations. N-goblin indicates a background light component that fluctuates at twice the frequency of the commercial frequency of fluorescent lamps and the like.

The first proposal is to detect the backlight level (Nl + Ng) at 1 m in Fig. 1 (A), immediately before irradiating the subject with an infrared beam, and immediately after that, irradiate the subject with infrared light and use it as a signal light. Back shadow light level St 10 (Nl + Ny)
Detected, (S 1+ (Nt 1 Nz)) - (N+
10 Nm) to detect the signal St.

The second proposal was made by focusing on the fact that the frequency component included in the signal light component has a higher frequency than the frequency component included in the background light.

The second proposal is to detect the peak position where the rate of change in the level of the background light is the lowest, and to illuminate the subject at that point.

In order to obtain higher accuracy with the device according to the first proposal, t
It is necessary to shorten the time difference between l and tl, and to shorten the signal generation period and the tb infrared beam irradiation time. In the second proposal as well, it is preferable to shorten the signal width. Trying to obtain high output light emission in a short period of time is
This may also be a burden on the light emitting element. Another problem is that the response of the circuit on the light receiving side also needs to be made faster.

SUMMARY OF THE INVENTION An object of the present invention is to propose a signal light detection circuit for a distance measuring device that solves the above problem by utilizing the periodicity of fluctuations in background light.

In order to achieve the above object, a signal light detection circuit line in a distance measuring device according to the present invention, a photoelectric conversion element in a distance measuring device that irradiates a light beam toward a subject and measures the distance by detecting the reflected light. and a first and ta2 detection circuit,
First and second switches connecting the first and second detection circuits to the photoelectric element, respectively, and the first switch are activated for a certain period of time at the same time as the light beam irradiation means are activated, A signal light component is extracted by comparing the outputs of the first and second detection circuits with a timing circuit that operates the second switch for a certain period of time after an integer ◆ of the period of pulsation of the commercial power supply frequency has elapsed. It consists of a comparison circuit.

According to the above structure, the object of the present invention can be completely achieved.

The present invention will be described in more detail below with reference to the drawings and the like.

FIG. 2 is a diagram showing an embodiment of a distance measuring device using the circuit according to the present invention. Lens 3. The LED 2° and the LED lighting circuit 1 constitute a light beam irradiation means. The LED lighting circuit 1 is activated by a signal from a timing circuit 6a included in the signal light detection circuit 6, lights the LED 2 for a certain period of time, and emits an infrared beam in the direction of the subject. A photoelectric conversion element 5 is arranged at a certain baseline length away from the lens 3. A photodiode array is used as this photoelectric conversion element 5. FIG. 4 shows an enlarged view of the photodiode array. In this example, four elements 5-1
1. 5-12. 5-13. 5-14 is used. The output of the photoelectric conversion element 5 is connected to a signal light detection circuit, which element the signal light reaches is detected, and the detected contents are stored in the register 8. The contents of the register 8 are decoded by the decoder 8, and a lens driving circuit 10 drives an objective lens (not shown) based on the decoded output.

Next, an embodiment of the signal light detection circuit will be described in detail with reference to FIG. FIG. 3 mainly shows the element 5- of the photoelectric conversion element 5.
A circuit portion for detecting signal light from the output of 11 is shown. The circuits that process the outputs of other elements are similarly configured and are therefore omitted. A photodiode, which is an element forming the photoelectric conversion element 5, is reverse biased as shown in FIG. The output photocurrent of the photodiode is converted into a spot voltage by a resistor 12 and connected to an amplifier 15 via a capacitor 13. The resistor 14 has a relatively high resistance value and serves as a discharge resistor that prevents charge from being accumulated in the capacitor 13 due to constant incident light. The output of the amplifier 15 is connected to a first detection circuit 6d via a first switch 6b, and to a second detection circuit 6e via a second switch 6C. First and second switch 6b
.

6c is composed of an analog switch and is a timing circuit 6a.
It is opened and closed by signals from The first detection circuit 6d includes a diode 16. Capacitor 18. Resistor R and width adjuster 1
9. A circuit is formed on the sample thread 2. The second detection circuit 6e includes a diode 17. Capacitor 20.
It includes a resistor R and an amplifier 21, and similarly forms a sample and hold circuit. The output of each detection circuit 6d, 6e is connected to a comparison circuit 6f. The output of the first detection circuit 6d is connected to the inverting input terminal of the amplifier 26 via the resistor 22.
The output of the second detection circuit 6e is connected via a resistor 24 to the non-inverting input terminal of the amplifier. Resistors 23 and 25 are connected to the amplifier 26, forming a differential amplifier circuit. The output of the amplifier 26 is connected to a comparator 30 through a resistor 27 and a capacitor 28.
．． ° 32 ° 33, respectively, are elements 5-1 of the photoelectric conversion element
2. -5-13. 5-14, each of which has its inverting input terminal connected to a reference voltage appearing across a resistor 29.

The operation of the embodiment apparatus having the above configuration will be explained with reference to FIG. FIG. 5(A) shows a state in which the signal light is superimposed on the back shadow light. Now, when the first timing pulse shown in FIG. 5(B) is applied from the timing circuit 6a at time t5 in FIG. 5, the first switch 6b is turned on by the width ΔT of the timing pulse. At this time, the first detection circuit 6d samples and holds the voltage (Ns+Nm) corresponding to the level of the background light at that time, as shown in FIG. 5(C). Then, when the timing circuit 6a generates the next timing pulse at time t6, the second timing pulse is generated first.
The second switch 6c opens at the same time as the light beam irradiation means described with reference to the figure is activated.

As a result, the 26th detection circuit 6 samples and holds a voltage corresponding to the level of the sum of the backlight light and the signal light (Ns +N snow) +S shown in Figure 5 (A) K (Figure 5 (D)).
reference). The output of the second detection circuit 6e and the output of the first detection circuit 6d are compared in a comparison circuit 6f, and at time t, the output of the comparator 30 is changed as shown in FIG. 5(E). Appears on the other side.

5-12 of other elements of photoelectric conversion element. 5-13. 5
-14 are similarly detected and the comparators 31, 32, .
33, the way it comes out appears in the same way. In addition, in this embodiment, the configuration is such that an output H appears on the comparator corresponding to the element that receives the reflected light of the light beam.
When -13 and 5-14 both receive signal light, the outputs of comparators 32 and 33 become H. These outputs are stored in a register 8 and decoded by a decoder 9.

As described above in detail, according to the present invention, it is possible to detect clearly distinguishing back shadow light and signal light.

The present invention is configured to perform sampling and detection corresponding to the period of the backlight, so if the sampling width and detection width are made the same, detection can be performed even if the width (ΔT) is made considerably large. No errors occur. Note that it is clear that there is no need to change the T even if the back shadow light does not pulsate.

In the embodiment, the interval between the output pulses of the timing circuit is made to coincide with one cycle of pulsation, but it can be set to an integer number of one cycle.

[Brief explanation of the drawing]

FIG. 1 is a ninth graph illustrating a conventional technique for distinguishing between background light and signal light, and FIG. 2 is a block diagram showing an embodiment of a distance measuring device using a signal light detection circuit according to the present invention.
Fig. 3 is a circuit diagram showing an embodiment of the signal light detection circuit, Fig. 4 is a schematic diagram showing an enlarged surface of a photoelectric conversion element, and Fig. 5 is for explaining the operation of the circuit shown in Fig. 3. FIG. 1ψ・-LED lighting circuit 2・・・LED 3.4e・・・Lens 5・・Photoelectric conversion element 6・Signal light detection circuit 6a11・・Timing circuit 6b・Fist first switch 6C・・Second Switches 6d...e First detection circuit 6C... Second detection circuit 6f... Comparison circuit 8... Register 9... Decoder 10... O lens drive circuit

Claims (1)

[Claims] In a distance measuring device that measures a distance by emitting a light beam toward a subject and detecting the reflected light, a photoelectric conversion element,
first and second detection circuits, first and second switches connecting the first and second detection circuits to the photoelectric element, respectively; Compare the outputs of the first and second detection circuits with a timing circuit that operates for a certain period of time and operates the second switch for a certain period of time after a period of time that is an integral multiple of the pulsation cycle of the power supply frequency for the startup descendants has elapsed. A signal light detection circuit in a device comprising a comparison circuit for extracting a signal light component.