JPS5834312A - Active type distance measuring device - Google Patents

Abstract

PURPOSE:To eliminate erroneous distance measurement by limiting the output of the output stage of a photodetecting circuit, which responds to even a DC input component to some extent, before the output stage enters into a saturated state against an excessive DC input component. CONSTITUTION:Two stages of diodes D1 and D2 connected in series are provided to the output stage of an emitter follower transistor (TR) Q1 to perform limiter operation at a voltage much higher than the reference voltage of a circuit output V0, i.e. the circuit output V0 with normal brightness. When a camera is directed to an excessive brightness subject, a limiter operates before the circuit output V0 is saturated, and variation in power voltage VCC never appears in the circuit output V0 through the TRQ1.

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 S information by projecting an alternating current modulated light beam and detecting the reflected light beam. It is something. .

Various types of active distance measuring devices such as those mentioned above have already been proposed, and some of them are actually used for autofocus i1 of cameras etc.
It is implemented in a one-section device.

As an example, a device having a basic structure as shown in FIG. 1 has already been proposed.

That is, in the figure, the projector 1 continuously projects infrared light using a light emitting diode, for example, to scan the object.The light receiving circuit 2 converts the reflected light from the object into an electrical signal. The bypass filter 3 attenuates low frequency components such as DC components, and the amplifier 4 further increases the output by +11!;i.

From the output signal power), the signal components at the time of projection and at the time of non-projection are synchronized with the frequency of intermittent projection of the infrared light, in the sample full hold circuit 7 and the sample bold circuit 5.
Sampling and vaulting. The output of the sample hold circuit 7, that is, the signal at the time of projection is transferred to the buffer 8.
After passing through the inverter 9, the output is inverted with respect to the calculation reference level, and the other sample hold time &5
The summing amplifier 10 adds and amplifies the output of the buffer 6, which is the 0 output signal, that is, the signal at the time of non-projection. The summing amplifier is an inverting amplifier. After the output direction is projected onto a low-pass filter 1 to attenuate high frequency components, a peak detector 12 detects the maximum value of the tortoise pressure.

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 spa such as a silicon photocell, and output a corresponding output voltage using an operational amplifier OP. The relationship between the current 1p of the light-receiving element spa and the output voltage vO of the circuit is expressed by the high-frequency cutoff frequency fnroq and the low-frequency cutoff frequency fL. W
is, 1 fllfQR-,,"'; Punishment also becomes, force 1) return resistance R, is Rx + 1'h f > f ■ J case of Gil] (y (n Tech GH) =
Rz +kpm 10R3f (for 'IIIW
El (Low) ” Ri + Rz dodoru (see Figure 3).

Here, in a feedback N path consisting of a simple resistor, V'o will quickly become saturated due to power supply voltage limitations due to the reception of the DC component, and in order to suppress the low frequency component 1(1t'f), This circuit suppresses the gain at high frequencies and increases the gain near the flashing frequency of the light.

For example, circuit constants are set so that saturation of the light receiving circuit output due to DC light does not occur at the brightness within the normal shooting range of a camera, etc., but the output stage is saturated in response to excessive DC components such as direct sunlight. , in the example of FIG. 2, the emitter follower output vo is 1 "source" 1Iff, EI:.

Fluctuations in Vaa 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 (REID) that directly flows a large current, and VCC is then used as a power source for other circuits via a ripple filter RP11', the voltage will still be V. The flashing of the infrared light emitting diode Il(K]) by the aK light projection control f11++ circuit LPO is unsuitable for small equipment, and has problems such as high manufacturing costs. Furthermore, even when a rising circuit or the like is used as a power source, it is similarly difficult to completely eliminate ripples that appear in the circuit power source, and in this case, the power waveform appears as the output of the light receiving circuit. I have a disability.

When the light receiving circuit output is saturated, if the ripple of VCO is sampled in synchronization with its frequency, the output signal after the above-mentioned arithmetic processing, for example, will have vo. Depending on the ripple waveform and sampling phase, a level will appear, resulting in incorrect 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, and this is actually the case with the half-open shutter program used in lens-shutter cameras. In this case, the depth of field is very deep, and it is expected that the object will almost always be in focus even if the object is stopped at the very close focus position or the infinite focus position Δ.

The present invention has been made in view of the above-mentioned circumstances, and is intended for use in automatic cameras, etc., which obtain distance information6 by projecting an alternating current modulated light flux and detecting the reflected light flux. As an active distance measuring device suitable as a focus adjustment device, the output stage of the light receiving circuit, which responds to a certain extent to DC input components, becomes saturated due to excessive DC input components such as direct sunlight from the burnout ink. It is an object of the present invention to satisfactorily eliminate the fear of erroneous distance measurement caused by signals other than distance information appearing as outputs, such as fluctuations in circuit power supply voltage, and for this purpose, the active distance measurement method of the present invention is used. The mounting is characterized in that an output limiting circuit is attached to the light receiving circuit so as to output a signal equivalent to no signal in response to an excessive DC input component.

Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS. 5 to 9.

First, FIGS. 5 and 6 show a basic embodiment of the present invention, in which "Otl is the power supply voltage, VR1-1 is the reference voltage of the operational amplifier, OP, OP is the operational amplifier, S, ,S.

is a light-receiving element such as a silicon photo cell for detecting reflected light, R1"" Re h resistor, 01*'I n capacitor, (h, Qm are NPN) transistor, DI, D,
, p, , D, j p is a diode, Il+Il is a current source, voke light receiving circuit output, a,
6 a).

In FIG. 5, two stages of diodes connected in series, D1+D2, are provided at the output stage of the emitter follower transistor Q1, and the circuit output V is obtained. ■ The circuit output at a voltage considerably higher than the reference voltage, i.e., normal brightness. The IJ miter (output limiting) function is performed at 2Vnm (Vine td diode forward voltage), which is a much higher voltage than the Vine td diode forward voltage.

When the camera is pointed at the subject, the circuit output V
.

V before it is saturated. >2VBl, the limiter operates and the '+IL source'f (E voltage V.C fluctuation does not appear in the circuit output ■o) via the transistor Qz.

Therefore, for example, no level appears at the peak detector input in the distance information processing system shown in FIG. 1.

V. When ≦2VD, the diode Dl+Da is off, the limiter does not operate, and normal distance measurement is performed.

When the limiter is connected as shown in Figure 5, a considerable amount of current may flow into the diode Dl + D+1 through the transistor Q0 when the limiter is activated.
For example, as shown in Figure 6: I) y, D4, DsO
The same objective can be achieved more preferably by providing a limiter with three stages of diodes connected in Tti rows.

In the embodiments shown in FIGS. 5 and 6, the current source T, 1°
, where α is the voltage drop at , the limiter operates as vo.

〉3vH1! This is limited to +α, but this is because the diode forward voltage is used as the limiter, but for example, the lJ limiter voltage can be set to any value by doing as shown in Figure 9 below. Therefore, the spirit of the present invention is not limited to the embodiment shown in FIG. 5.6.

7, 8 and 9 show modified embodiments of the embodiments of FIGS. 5 and 6. FIG. ■. . is the tolerance voltage, V
RICFm is the reference voltage n of the operational amplifier, VRIF++ is the limiter operating reference voltage, OFa 10F 4 # O
Fs is an operational amplifier, SB, s, and lsa are light receiving elements, H0 to RIQtri resistors, and 0.

0,. 0. are capacitors, Q and s are IJPN) transistors, 001 comparators, 2 are elements such as diodes, and Voi; is the light receiving circuit output.

Fig. 7 shows an example in which an arbitrary number of serially connected diodes are connected to the feedback circuit to perform a limiter, Fig. 8 an example in which n diodes are connected in series to the rJ output stage to form an nVBsi limiter, and Fig. 5 This is an example in which the operating voltage of the IJ limiter can be set arbitrarily depending on the voltage of VRIFg, and the limiter is operated at tlFg.

Furthermore, the purpose of the modified embodiment shown in FIG. 7 is not limited to the use of two diodes as elements in the feedback loop, but any nonlinear element may be used.

As detailed above, according to the four inventions, an active distance measuring device that obtains distance information by projecting an alternating current modulated light beam and detecting the reflected light beam can be used with respect to a direct current input component. This is because the output stage of the photodetector circuit, which responds to a certain degree, becomes saturated with excessive DC input components due to direct sunlight, etc., and signals other than range information, such as fluctuations in the circuit power supply voltage, appear as the output. In particular, when an automatic focusing device such as a camera is intended, the aperture aperture is generally made smaller under high brightness, and the density is therefore deepened. From this point of view, the speed ratio Il in this case is extremely useful in view of the rational control mode of lens control to the in-focus position or the combined focus position. It also has the advantage of being extremely simple in circuit configuration and extremely inexpensive.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of an example of an active distance measuring device that has been proposed in the past. FIG. 2 is a partial circuit connection diagram showing a specific example of the light receiving circuit shown in FIG. 1. 2 is a diagram showing the relationship between the ω return resistance and the cutoff frequency of the light receiving circuit shown in FIG. 4, and FIG. 4 shows an example of the light projecting system shown in 8 and 9 are partial circuit connection diagrams showing an embodiment of the present invention. Sx, opl, ox +Qz * RI NRa'
S, tOPa, ol +Qg, R,”Re;
SB, 0P3ICs + Rezaki 11' S410P41
041R口″-t(it*SB+Op5夛Oa
1R15~Rxy ----- Received light amount r (7) 'j
ilt G, GJ, 1)1. Dg; DB~
Da ; Z ; J)n ~D++y+ ;0011
RIQIR191Q3, - Components of the output limiting circuit.

Claims (1)

[Claims] In an active distance measuring device that obtains distance information by projecting an alternating current modulated light beam and detecting the reflected light beam, an excessive DC input is applied to a light receiving circuit that responds to a certain degree to a DC input component. An active distance measuring device characterized in that an output limiting circuit is attached to the component so as to output a signal equivalent to no signal.