JPS6360884B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active distance measuring device, and particularly to an active distance measuring device that obtains distance information by projecting an alternating current modulated light beam and detecting the reflected light beam. It is.

Various types of active distance measuring devices as described above have already been proposed, and some of them are actually implemented in automatic focusing devices such as cameras.

As an example, an apparatus having the basic configuration shown in FIG. 1 has already been proposed.

That is, in the figure, an object is scanned while a projector 1 intermittently projects infrared light using, for example, a light emitting diode. The light receiving circuit 2 converts and amplifies the reflected light from the object into an electrical signal, and the high-pass filter 3 attenuates low frequency components such as DC components, and the amplifier 4 further amplifies the output.

From the output signal, signal components during projection and during non-projection are sampled and held in sample hold circuit 7 and sample hold circuit 5, respectively, in synchronization with the frequency of intermittent projection of infrared light. After passing the output of the sample hold circuit 7, that is, the signal at the time of projection, through the buffer 8, the inverter 9 outputs the output inverted with respect to the calculation reference level, and the output of the other sample hold circuit 5, that is, the signal at the time of non-projection. Batsuhua 6 which is a signal
The summing amplifier 10 adds and amplifies the outputs of the . Summing amplifier 10 is an inverting amplifier. After the output is applied to a low-pass filter 11 to attenuate high frequency components, a peak detector 12 detects the maximum voltage value.

For example, as shown in FIG. 2, the light receiving circuit 2 is configured to convert received light into a current using a light receiving element SPC such as a silicon photocell, and output a corresponding output voltage using an operational amplifier OP. The relationship between the current i _p of the light receiving element SPC and the output voltage vo of the circuit is expressed as (R ₁ + R ₂ + jwcR ₁ R ₂ /1 + jwcR ₃ ) · i _p +V _REF , and the high cut-off frequency _HIGH and the low cut-off frequency _LpW is _HIGH = 1/2πCR _{3 LpW} = R ₁ + R ₂ / 2πC (R ₁ + R ₂ + R ₂ R ₃ + R ₃ R ₁ ), and the feedback resistance R _F is ≫ If _HIGH , R _F(HIGH) = R ₁ +R ₂ +R ₁ +R ₂ /R ₃ ≪ In the case of _LpW , R _F(LpW) = R ₁ + R ₂ (see Figure 3).

Here, in a feedback circuit consisting of only a simple resistor, Vo will quickly saturate due to the limitation of the power supply voltage due to the reception of the DC component, and in order to suppress the noise of low frequency components, the gain at low frequencies will be suppressed. This is a circuit that increases the gain near the flashing frequency of the light.

For example, circuit constants are set so that the output of the light-receiving circuit does not saturate due to direct current light at the brightness within the normal shooting range of a camera, etc., but the output stage becomes saturated for excessive direct current components such as direct sunlight. , in the example shown in Figure 2, the power supply voltage is applied to the emitter follower output Vo.
Fluctuations in V _cc will appear as they are.

On the other hand, for example, as shown in Fig. 4, if battery B is used as a power source for an infrared light emitting diode IRED that directly flows a large current, and V _cc is then used as a power source for other circuits via a ripple filter RPF, the V _cc Ripples appear in synchronization with the blinking of the infrared light emitting diode IRED by the light projection control circuit LPC. ripple filter
Increasing the performance of RPF requires a complicated circuit configuration, making it unsuitable for small devices, and increasing manufacturing costs. Furthermore, even when a booster circuit or the like is used as a circuit power supply, it is similarly difficult to completely eliminate ripples that appear in the circuit power supply, and even in this case, there is a problem in that the power supply waveform appears as the output of the light receiving circuit.

When the output of the photodetector circuit is saturated, if the ripple of V _cc is sampled in synchronization with its frequency, the output signal that has completed the arithmetic processing described above, for example, will have V _cc
Depending on the ripple waveform and sampling phase, a level will appear, resulting in erroneous distance measurement.

On the other hand, in a camera, in order to obtain proper exposure when photographing a high-brightness subject, it is necessary to use a small aperture aperture, and this is actually the case with programs using half-open shutters used in lens shutter cameras. In this case, the depth of field is very deep, and it is expected that the lens will almost always be in focus even if the lens is stopped at the distance focus position or the infinity focus position.

The present invention has been made in view of the above-mentioned circumstances, and is an automatic focus adjustment system for cameras, etc., which obtains distance information by projecting an alternating current modulated light flux and detecting the reflected light flux. As an active distance measuring device suitable for use as a device, the output stage of the light receiving circuit, which responds to a certain degree to DC input components, becomes saturated due to excessive DC input components such as direct sunlight, and the output of the circuit is Fluctuations in power supply voltage, etc.
The purpose of the active distance measuring device of the present invention is to eliminate concerns about erroneous distance measurement due to the appearance of signals other than distance information. In contrast, the present invention is characterized in that an output limiting circuit is attached so as to output a signal equivalent to no signal.

Hereinafter, the fifth to fifth preferred embodiments of the present invention will be explained.
This will be explained with reference to FIG.

The following embodiment corresponds to the light receiving circuit 2 shown in FIG. 1, and the other circuit configurations are the same as those described above, so the explanation will be omitted.

First, FIGS. 5 and 6 show a basic embodiment of the present invention, where V _cc is the power supply voltage, V _REF1 is the reference voltage of the operational amplifier, OP ₁ and OP ₂ are the operational amplifiers, S ₁ ,
S ₂ is a light receiving element such as a silicon photo cell for detecting reflected light, R ₁ to R ₈ are resistors, C ₁ and C ₂ are capacitors,
Q ₁ , Q ₂ are NPN transistors, D ₁ , D ₂ , D ₃ , D ₄ ,
D ₅ is a diode, I ₁ and I ₂ are current sources, and Vo is a light receiving circuit output.

In Figure 5, the emitter follower transistor
Two stages of diodes are provided in the output stage of Q ₁ by connecting D ₁ and D ₂ in series, and the voltage is much higher than the reference voltage of the circuit output Vo, that is, 2V, which is much higher than the circuit output Vo at normal brightness. _BE ( _VBE is diode forward voltage) acts as a limiter (output limit). When the camera is pointed at an excessively bright subject, before the circuit output Vo saturates, a limiter is activated when Vo > 2V _BE , and the fluctuation of the power supply voltage V _cc synchronized with the blinking of the infrared light emitting diode through transistor Q ₁ becomes the circuit output. It never appears in Vo. In other words, a constant light-receiving circuit output Vo is output to the subsequent circuit, regardless of the reception state of the projected infrared light received by the light-receiving elements S ₁ and S ₂ and unaffected by fluctuations in the power supply voltage V _cc .

Therefore, for example, no level appears at the peak detector input in the distance information processing system shown in FIG. 1. When Vo≦2V _BE , the diodes D ₁ and D ₂ are off, the limiter does not operate, and normal distance measurement is performed.

If a _limiter connection is made as shown in Fig. 5, a considerable amount of current may flow into the diodes D ₁ and D ₂ through the transistor Q ₁ when the limiter is activated. ₄ , _D5
The same objective can be achieved more preferably by providing a limiter with three stages of diodes connected in series.

In the embodiments shown in FIGS. 5 and 6, the current source
Assuming the voltage drop at I ₁ and I ₂ to be α, the limiter operates only when V _cc > 3V _BE + α, but this is because the limiter happens to use a diode forward voltage. By doing as shown in FIG. 9, the limiter voltages can be set in any order, so the gist of the present invention is not limited to the embodiments shown in FIGS. 5 and 6.

7, 8 and 9 show modified embodiments of the embodiments of FIGS. 5 and 6. FIG. V _cc is the supply voltage, V _REF1 is the operational amplifier reference voltage, V _REF2
is the limiter operating reference voltage, OP ₃ , OP ₄ , OP ₅ are operational amplifiers, S ₃ , S ₄ , S ₅ are light receiving elements, R ₉ to R ₁₉ are resistors, C ₃ , C ₄ , C ₅ are capacitors, Q ₃ is an NPN transistor, CO ₁ is a comparator, Z is an element such as a diode, and Vo is the output of the above circuit.

Figure 7 shows an example in which an arbitrary number of series-connected diodes are connected to the feedback circuit to perform the same limiter as described above, and Figure 8 shows an example in which n diodes are connected in series to the output stage and a similar limiter is configured with nV _BE . FIG. 9 shows an example in which the operating voltage of the limiter can be set arbitrarily depending on the voltage of V _REF2 , and the limiter is operated at V _REF2 .

Furthermore, the gist of the modified embodiment shown in FIG. 7 is that the element Z in the feedback loop is not limited to a diode, but may be any nonlinear element.

As detailed above, according to the present invention, as an active distance measuring device that obtains distance information by projecting an alternating current modulated light beam and detecting the reflected light beam, The output stage of the photodetector circuit, which responds to a certain degree, becomes saturated with excessive DC input components caused by direct sunlight, etc., and errors occur when signals other than distance information, such as fluctuations in the circuit power supply voltage, appear as the output. This effectively eliminates concerns about distance measurement, and especially when intended for automatic focus adjustment devices such as cameras, the aperture aperture is generally made smaller under high brightness, and the density is therefore deepened. From this point of view, it is extremely useful in view of the rational control mode of controlling the lens to a long-distance focusing position or an infinite focusing position in this case. It also has the advantage of being extremely simple in circuit configuration and extremely inexpensive.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of an example of a conventionally proposed active distance measuring device, FIG. 2 is a partial circuit connection diagram showing a specific example of the light receiving circuit shown in FIG. 1, and FIG. 2 is a diagram showing the relationship between the feedback resistance and cut-off frequency of the light receiving circuit shown in Figure 4, Figure 4 is a diagram showing an example of the light projecting system shown in Figure 1, Figures 5, 6, and 7
8 and 9 are partial circuit connection diagrams showing embodiments of the present invention. S ₁ , OP ₁ , C ₁ , Q ₁ , R ₁ to R ₄ ; S ₂ , OP ₂ , C ₂ ,
Q ₂ , R ₅ ~ _{R 8} ; S ₃ , OP ₃ , C ₃ , R ₉ ~ _{R 11} ; S ₄ ,
_OP4 , _C4 , _R12 ~ _R14 ; _S5 , _OP5 , _C5 , _R15 ~ _R17 ...
...Components of the light receiving circuit, D ₁ , D ₂ :D ₃ to _{D 5} :z:
D _o ~ _{D 2o} ; CO ₁ , R ₁₈ , R ₁₉ , Q ₃ ... Components of the output limiting circuit.

Claims (1)

[Claims] 1. An active ranging device that obtains distance information by projecting an alternating current modulated light beam and receiving its reflected light beam, which is driven by the power source for projecting the alternating current modulated light beam; a light receiving circuit for receiving the reflected light flux; detecting that an excessive DC light component is input to the light receiving circuit when the output level of the light receiving circuit reaches a predetermined value;
When the output level of the light receiving circuit reaches a predetermined value, a constant signal is sent to a subsequent circuit for obtaining the distance information, regardless of the light receiving state of the light receiving circuit and unaffected by fluctuations in the power supply output. An active distance measuring device comprising: a determination circuit that outputs an output.