JPS6234082B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a distance detection device used in a camera or the like.

As a distance measuring method for autofocus (automatic focus adjustment) in so-called compact cameras, a passive double image matching method using external light has become mainstream. However, the essential element of this double image matching method using the passive method is the use of a movable mirror to change the relative position of one image with respect to the other image.
The use of this movable mirror has poor durability, and since it uses a double image matching method, distance measurement is performed based on contrast information of the subject (distance measurement target), so it is highly dependent on the subject, and it is difficult to capture objects with poor contrast. There were problems with the distance measurement and poor distance measurement ability in dark conditions. Further, in a system having such a movable part, adjustment becomes complicated and requires a lot of effort.

In addition, although the triangulation method using an active method in which light is emitted from the ranging device itself improves the subject dependence described above, Those having movable parts such as the above cannot avoid problems such as poor durability and complicated adjustment as described above.

On the other hand, there is a device as shown in FIG. 1 that uses an active triangulation method and has no moving parts. This is the light emitting part 1
Light such as infrared light projected from the distance measuring target 2 (2a,
2b, 2c, 2d, etc.), and this reflected light is transmitted to a plurality of light receiving elements, for example, four light receiving elements 3a, 3b, 3c, 3.
The distance of the object to be measured is determined by which light receiving element of the light receiving section 3 consisting of d receives the light.

This method has no moving parts, so it can be said that there are almost no problems in terms of durability, adjustment, etc. However, in this case, there is a fatal problem that the distance resolution is limited because the light receiving section 3 is quantized. For example, if the light receiving section 3 is made up of four light receiving elements 3a to 3d as shown in FIG. 1, only seven zones can be formed even if the intermediate positions of each of the light receiving elements 3a to 3d are included. If errors are taken into account, it is expected to be even worse than this.

On the other hand, as a type of active method, there is an ultrasonic method that measures the distance of the object by emitting ultrasonic waves, receiving reflected waves from the distance measurement object, and measuring the time required for transmission and reception. Although it is easy to process because it measures ultrasonic waves, it requires high-output transmission and a large power source. For example, it is difficult to effectively transmit ultrasonic waves using a power source used in a compact camera or the like. In addition, in order to prevent the ultrasonic waves from hitting objects other than the distance measurement target and reducing the distance measurement accuracy, it is necessary to improve the directivity. This is also a big problem for compact cameras and the like.

On the other hand, the following distance detection device can be considered as one that does not require much power, is easy to adjust, has good durability, and can provide high distance resolution.

That is, this distance detection device is provided at a location where a light source that projects pulsed light onto a distance measurement target and a spot of reflected light of the pulsed light by the distance measurement target is imaged, and performs the measurement based on the parallax between the light source and the light source. Semiconductor optical position detection that continuously detects the position of an incident spot according to the distance of a target in the direction of position change due to the change in distance, and obtains first and second current outputs having a mutual current ratio according to the detected position. a first detection circuit that receives the first current output of the PSD and logarithmically converts and outputs a variation in the first current output due to the pulsed light; a second detection circuit that receives the second current output of the PSD and logarithmically transforms and outputs a variation in the second current output due to the pulsed light; and a difference detection circuit that obtains a distance detection signal by calculating the difference between the logarithmically converted fluctuations of the first and second current outputs.

This distance detection device will be explained in detail with reference to FIGS. 2 to 6.

In FIG. 2, 4 is a pulse light emitter. This pulse light emitter 4 is invisible to the eye.
From the viewpoint of the sensitivity of PSD5, it is desirable to use one that generates infrared light. The pulsed light emitted from the pulsed light emitter 4 passes through the projection lens 6 to the object 7 (7) to be measured.
a, 7b, 7c, etc.). The pulsed light reflected by the subject 7, that is, the reflected light, is sent to the light receiving lens 8.
The incident image is formed on the PSD 5 via. This PSD
5 is a planar-type PIN photodiode manufactured using ion implantation technology that has one-dimensional continuous position resolution, and is ``position sensitive''.
There are two types of elements: one-dimensional type and two-dimensional type, but either type can be used as it is sufficient to perform one-dimensional position detection.As shown in the figure, 5 for position 7a of subject 7 and 5a for PSD 5 and 7b for PSD 5
b, . . . reflected light spots are imaged at positions 5d relative to infinity. This PSD 5 can determine the incident position of a light spot from the ratio of two current outputs, for example, as shown in Figure 3a.
When a light spot enters the center position _S1 of the light receiving surface of PSD5, the ratio of the two current outputs I _L1 and I _L2 is I _L
1 /I _L2 = 1, and if it is incident on position S ₂ as shown in b in the figure, I _L1 /I _L2 = 1/2, and if it is incident on position S ₃ as in c in the same figure, I _L1 /I _L2 =2.

In FIG. 2, the distance between the light emitting lens 6 and the light receiving lens 8, that is, the base line length, is l, the distance from the light receiving lens 8 to the PSD 5 is f, the distance from the light emitting lens 6 to the subject 7 is T, PSD5 for that
If the distance from the position 5d corresponding to infinity of the upper light spot is P, then T=f·l/P (1) holds true. Since the position of the light spot imaged on the PSD 5 corresponds to the ratio of the two current outputs obtained from the PSD 5, information on the subject distance T can be obtained from these two current outputs.

Here, the detection current ratio I of subject distance T and PSD5 is
When looking for the relationship with _L1 /I _L2 , if the total length of PSD5 is a unit length (that is, 1), then T・I _L1 /I _L1 +I _L2 = f・l ...(2), It can be seen that the relationship y=1/x+K is as shown in FIG.

By the way, there is no problem when measuring distance in a pitch-dark place, but during general photography, etc., there is a steady light with a much higher light intensity than the pulsed light from the pulsed light emitter 4, so the reflected light of the pulsed light is Extraction becomes impossible. Therefore, in this case, the first detection circuit 9 receiving the first current output of the PSD 5 and
A second detection circuit 10 receiving the second current output of the PSD 5 removes the influence of stationary light, and logarithmically transforms and extracts the fluctuations in the photocurrent due only to the reflected light of the pulsed light. A distance detection signal corresponding to the current ratio of the first and second current outputs of the PSD 5 is output by taking the difference.

FIG. 5 shows the PSD 5 and the first and second detection circuits 10,
11 shows the detection head section of No. 11.

Figure 5 shows PSD5 as an equivalent circuit.
-1 is a surface resistance, 5-2 is a parallel resistance, 5-3 is a junction capacitance, 5-4 is an ideal diode, and 5-5 is a current source. The photocurrents I _L1 and I _L2 generated from the PSD 5 are transferred to logarithmic conversion units LA _{1 and LA 2, each consisting of a logarithmic conversion transistor Tr 1 and} an operational amplifier OA ₁ , and a logarithmic conversion transistor Tr ₂ and _{an operational amplifier OA 2 .}
is logarithmically transformed and output as the following outputs V _L1 and V _L2 .

V _L1 =-kT/q・lnI _L1 /I _S ...(4) V _L2 =-kT/q・lnI _L2 /I _S ...(5) (where, k: Boltzmann's constant, T: absolute temperature,
q: electron charge, _IS : emitter saturation current of transistors Tr ₁ and Tr ₂ . ) The reason for performing logarithmic transformation in this way is to enable a wide dynamic range and to easily calculate the ratio of both outputs by simply taking the difference.

Next, the logarithmic conversion output V obtained in this way
FIG. 6 shows the configuration of a detection circuit including a circuit for removing the influence of stationary light from _L1 and V _L2 .

Although FIG. 6 is provided for both the first current output I _L1 and the second current output I _L2 of the PSD 5, only the first detection circuit 9 on one I _L1 side is shown here. A second detection circuit 10 having exactly the same configuration is provided on the I _L2 side as well. In Fig. 6, in the steady state, the steady photocurrent I _L1
r flows into transistor Tr ₁ , but the transistor
The same current also flows through Tr ₃ via transistor Tr ₄ . At this time, the switch SW ₁ is closed, and feedback is applied to the operational amplifier OA ₃ via the operational amplifier OA ₄ and transistors Tr ₅ and Tr ₄ that constitute a voltage follower, so the potential at point A in the figure is Vb. The voltage is fixed at the potential at point B in the diagram.

Next, the pulse light emitter 4 generates pulse light and at the same time the switch SW ₁ is opened. At this time, the base potential of the transistor Tr ₄ is held by the capacitor C ₁ at a value equal to that in the steady state, and the steady photocurrent I _L1r is still applied to the transistor Tr 4 .
The signal continues to be supplied from Tr ₄ to transistor Tr ₃ . Then, a variation ΔI _L1 of the photocurrent I _L1 that captures the reflected light of the pulsed light is supplied from point B to the transistor Tr ₃ via the diode D ₁ . By the way, A
The potential Va ₁ at the point is Va ₁ =Vb-kT/qlnΔI _L1 /I _S (6) (However, I _S in this case is the reverse current of the diode D _1. ). In this way, only the variation ΔI _L1 of the photocurrent I _L1 can be extracted. Va ₂ corresponding to the variation ΔI _L2 of the photocurrent I _L2 similar to this Va ₁ is PSD5.
The second photocurrent output I _L2 side second detection circuit 10
Therefore, by calculating these differences in the difference detection circuit 11, Va ₁ −Va ₂ =kT/qlnΔI _L1 /I _S −kT/qlnΔI _L2 /I _S =kT/qlnΔI _L
1 /ΔI _L2 (7), and only the ratio of the photocurrent due to the reflected light of the pulsed light is determined.

With such a configuration, distance measurement can be performed by detecting only the variation in photocurrent caused by pulsed light.

However, the first configuration shown in FIG.
There is no particular problem with the detection circuit under ideal conditions, but the collector-emitter voltage V _CE - collector current Ic characteristic of the PNP transistor used as transistor Tr ₄ is as shown in Figure 7, where V _CE is ΔV.
When ΔI changes, Ic also changes slightly as shown in the figure ΔI. Therefore, for example in steady state Vb
If the potential of is set to OV and the collector voltage Vc of the PNP transistor Tr ₄ drops to -2V during pulse emission, the variation in V _CE will be 2V, and the variation in Ic will be a considerably large value. This phenomenon becomes more problematic as the amount of constant light increases.

The present invention has been made in view of the above circumstances, and eliminates the above-mentioned problems related to the characteristics of the transistor in the first and second detection circuit parts that logarithmically convert only the variation due to pulsed light from the PSD output. The object of the present invention is to provide a distance detection device that is stable.

That is, from the feature of the present invention, the first and second detection circuits each include a first transistor for logarithmic compression whose collector is supplied with an input current signal, and a collector of the first transistor. a first operational amplifier connected to its inverting input terminal and its emitter connected to its output terminal; a second transistor whose emitter is connected to the output terminal of this first operational amplifier; and a collector of this second transistor. a second operational amplifier connected to an inverting input terminal; a current supply circuit that uses the output voltage of the second operational amplifier as a control voltage and supplies current to the collector of the second transistor in accordance with this voltage; a capacitor that holds the control voltage for the current supply circuit, and a current corresponding to the fluctuation of the input current signal from the output of the second operational amplifier to the collector of the second transistor only when pulsed light from the light source is received. A diode or a third
transistor, and the detection output is taken out from the output terminal of the second operational amplifier.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 8 shows the configuration of the first and second detection circuits which are the main parts in the first embodiment of the present invention. Note that since the first and second detection circuits 9 and 10 are configured in exactly the same way, the first detection circuit 9 is
Only the configuration is shown.

As shown in FIG. 8, the first current output I _L1 of the PSD 5 is connected to the logarithmic compression transistor Tr ₁ and the operational amplifier
V _L1 is logarithmically converted through the logarithmic compression transistor Tr ₁ of the logarithmic conversion unit LA ₁ consisting of OA ₁ and is expressed in equation (4).
The output becomes =-kT/q·lnI _L1 / _IS . The same current as the current I _L1 flows from the power supply +Vcc through an N-MOS FET (N-MOS field effect transistor) FT ₁ and is expanded by an expansion transistor Tr ₃ .
At this time, if the base potential of transistor Tr ₃ is made approximately 60 mV higher than the base potential of transistor Tr ₁ , a 10 times expansion current can be obtained, and if the emitter area of transistor Tr ₃ is made twice that of transistor Tr ₁ , This results in twice the extension current.
Here, the explanation will be made assuming that the image is not particularly expanded (1 times expanded).

In a steady state, switch SW ₂ is closed and switch SW ₃ is open. Therefore, N-MOS
The source potential of the FET FT ₁ is fixed to the potential Vc of the non-inverting input terminal of the operational amplifier OA ₅ because feedback is applied to the operational amplifier OA ₅ .

Next, the switch is activated at the same time as the pulsed light is emitted.
Open SW ₂ and close switch SW ₃ . Due to the charge accumulated in the capacitor _C2 when steady light is incident, N
- Since the gate potential of the MOS FET FT ₁ is fixed, the steady-state photocurrent I _L1 r is supplied to the transistor Tr ₃ by this FET FT ₁ . The current change amount ΔI _L1 due to the pulsed light is supplied from the operational amplifier OA ₅ through the diode D ₂ . At this time, since feedback is applied to the operational amplifier OA ₅ in a loop via the diode D ₂ , the gate-source voltage V _GS of the FET FT ₁ does not change. This state is expressed as an operational amplifier.
If we consider the output Vo derived from the output end of OA ₅ , we will see that it changes as shown in Figure 9. In other words, in the steady state, Vo ₁ = Vc + V _GS ( _ID = I _LS ) ... (8), and when pulsed light is transmitted and received, Vo ₁ = Vc + kT / qln (ΔL _L1 / I _S ) ... (9) (However, I _S is the reverse current of the diode D _2. ) It can be seen that the following is true.

There is a second detection circuit 10 configured in exactly the same way on the second current output I _L2 side of the PSD5, and its output is
Set it to Vo ₂ .

The outputs Vo ₁ and Vo ₂ obtained in this way are the first
0 is applied to the difference detection circuit 11 shown in FIG. 1st
In FIG. 0, the signals Vo ₁ and Vo ₂ are led to an operational amplifier OA ₆ configured as a differential amplifier to obtain the following voltage signal V _DO .

V _DO =Vo ₁ −Vo ₂ =Vc+kT/qlnΔI _L1 /I _S −(Vc+kT/qln
ΔI _L2 /I _S ) =kT/qln (ΔI _L1 /ΔI _L2 ) (10) In this way, the current ratio corresponding to the distance is obtained as the voltage value V _DO . This voltage V _DO is generated by a sample-hold circuit section SH shown in FIG. 10, which includes a sample switch SW ₄ , a holding capacitor C ₃ , and an operational amplifier OA ₇ that constitutes a voltage follower as a buffer. It is sufficient to sample and hold during the light emission period, but if a light emitting diode or the like is used as the light emitting element, the light emitting efficiency will drop significantly due to a rise in the temperature of the junction, so it is better to sample immediately after light emission to obtain better results. . This method of sampling immediately after light emission is also effective when a periodic component (pulsating light component) of the power source is present in the ambient light source.

Since the sampled output has a voltage proportional to the distance, it can be used as a distance signal for automatic focus adjustment control, display, etc.
Alternatively, a comparator or the like may be used to convert the signal into a signal divided into a plurality of distance zones for each appropriate level.

In the manner described above, the influence of stationary light can be effectively and stably removed, and highly accurate distance measurement becomes possible. In addition, the configurations used for the first and second detection circuits do not use junction FETs, which are not suitable for IC implementation, but are composed of MOSFETs, bipolar transistors, operational amplifiers, diodes, etc., so IC implementation is also possible. It's easy.

Note that the present invention is not limited to the embodiments described above, and various modifications can be made.

For example, as a second embodiment of the present invention, as shown in FIG. 11, an operational amplifier configured as a voltage follower in place of the N-MOS FET FT ₁ in FIG.
A combination configuration of OA ₈ and NPN transistor Tr ₆ may also be used. In such a configuration, a bipolar process is sufficient when converting to an IC.
It becomes easier to

As a third embodiment of the present invention, as shown in FIG. 12, a Darlington connection configuration of NPN transistors Tr ₇ and Tr ₈ may be used instead of the N-MOS FET FT ₁ of FIG. 8. This case also has almost the same advantages as the second embodiment.

Furthermore, as a fourth embodiment, it is conceivable that the function of the operational amplifier OA ₅ in FIG. 8 is shared by two operational amplifiers OA ₉ and OA ₁₀ as shown in FIG. 13.

In Fig. 13, in the steady state, switch SW ₂
is closed, and the input voltage Vx to the non-inverting input terminal of operational amplifier OA ₉ is set lower than the input voltage Vref to the non-inverting input terminal of operational amplifier OA ₁₀ , and the output voltage Vo' is set to "L" (low). level). In this way, no current flows through the logarithmic compression diode _D3 , but current flows through the N-MOS FET _FT1 to the transistor _Tr3 . and,
Open switch SW ₂ at the same time as projecting the pulsed light.
Let Vx be equal to Vref. By doing this, the current due to the pulsed light is transferred to the diode D ₃
As a flow output Vo', a voltage of Vo'=Vref+kT/qlnΔI _L1 /I _S (11) (where I _S is the reverse current of the diode D ₃ ) is obtained.

In addition, in the configuration shown in Fig. 13, the switch
For SW ₂ , if the pulse emission is extremely short,
It can be omitted by increasing the time constant of the system, so
It is possible to replace it with high resistance.

In addition, in the configuration of FIG. 8, the diode D ₂
If used as is, the offset voltage of operational amplifier _OA5 will appear at the output. In other words, the amount of offset
If Vof and the voltage drop across diode _D2 are _VD , then Vo=Vc+Vof+ _VD (12). At this time, if there is a difference in offset voltage between the first and second detection circuits on both sides of the PSD 5, the error in the output after differential processing will become large. Therefore, as a fifth embodiment of the present invention, as shown in FIG.
PNP transistor Tr ₉ replaces diode D ₂ in the diagram
_{If the configuration uses _} It will be done. In addition, at this time, the switch
SW ₅ should be closed only when pulsed light is emitted. The reason is that if the base of the transistor Tr ₉ is always grounded, a current will flow between the collector and base of the transistor Tr ₉ in a steady state.

As described in detail above, according to the present invention, it is possible to eliminate defects related to transistor characteristics and to stabilize the first and second detection circuit portions that logarithmically transform only the variation due to pulsed light from the PSD output. A distance detection device can be provided.

[Brief explanation of the drawing]

1 to 7 are diagrams for explaining the prior art and its problems, FIG. 8 is a circuit diagram showing the main part configuration of the first embodiment of the present invention, and FIG. 9 is a diagram of the same embodiment. An operation waveform diagram for explaining the operation, FIG. 10 is a circuit diagram showing the configuration of other main parts of the same embodiment, and FIG.
FIG. 12, FIG. 13, and FIG. 14 are circuit diagrams showing the main part configurations of the second, third, fourth, and fifth embodiments of the present invention, respectively. OA ₁ , OA ₅ ~ OA ₁₀ ... operational amplifier, Tr ₁ ,
_Tr3 , _Tr6 to _Tr9 ...transistor, _FT1 ...MOS
FET, SW ₂ to _{SW 5} ... switch, D ₂ , D ₃ ... diode, C ₂ , C ₃ ... capacitor.

Claims (1)

[Claims] 1. A light source that projects pulsed light onto a distance measurement target, and a light source that is provided at a location where a reflected light spot of the pulsed light from the distance measurement target is imaged, and that corresponds to the distance of the distance measurement target based on the parallax with the light source. a semiconductor optical position detector that continuously detects the position of the incident spot in the direction of position change due to the change in distance and obtains first and second current outputs having a mutual current ratio according to the detected position; receiving the first current output of the detector and receiving the first current output by the pulsed light;
The first step is to logarithmically transform and output the variation in the current output of
a detection circuit that receives the second current output of the semiconductor optical position detector and detects the second current output by the pulsed light.
A second circuit that logarithmically transforms and outputs the variation in the current output of
and a difference detection circuit that obtains a distance detection signal by calculating the difference between the logarithmically converted fluctuations in the first and second current outputs output from the first and second detection circuits. In the distance detection circuit, each of the first and second detection circuits includes a first transistor for logarithmic compression whose collector is supplied with an input current signal, and a collector of the first transistor connected to an inverting input terminal. a first operational amplifier whose emitter is connected to the output terminal; a second transistor whose emitter is connected to the output terminal of the first operational amplifier; and a collector of the second transistor connected to the inverting input terminal. a second operational amplifier, a current supply circuit that uses the output voltage of the second operational amplifier as a control voltage and supplies current to the collector of the second transistor in accordance with this voltage; a capacitor that holds a control voltage, and a current that corresponds to a variation in the input current signal is supplied from the output of the second operational amplifier to the collector of the second transistor only when pulsed light from the light source is received, and the current value is supplied to the collector of the second transistor. A distance detection device comprising: a diode or a third transistor that produces a voltage drop corresponding to the logarithm of , and an output is taken out from an output terminal of the second operational amplifier.