JPH0334005B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is a non-scanning type semiconductor optical position detection device (Position Sensitive Detector, hereinafter referred to as PSD).
This invention relates to a distance measuring device using a distance measuring device.

First, the basic structure of the PSD will be briefly described with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram showing the configuration of the PSD, and FIG. 2 shows an equivalent circuit of the PSD. PSD has a pair of detection electrodes (anode) as shown in Figure 1.
A, B and a common electrode C (cathode). When light is incident at a position x ₁ from electrode A, a current with a value inversely proportional to the distance to electrodes A and B flows. When the current from A is i _A and the current from B is i _B , the following equation (1) holds true.

i _A /i _B =x ₂ /x ₁ ...(1) Figure 2 shows the equivalent circuit of PSD. That is,
PSD can be expressed as photodiodes facing each other. Figure 3 shows an example of a distance measuring device using a PSD. Let the distance to the object be l, and the light emitting element LED
Let d be the distance to the PSD, that is, the baseline length, d ₁ be the dimension of the PSD, and l ₁ be the distance between the lens and the PSD.
Assuming that the currents from the A and B electrodes are i _A and i _B , respectively, and the position of the light spot imaged on the PSD is x ₁ from the electrode A, the following relationship holds between them.

l/d=l ₁ /x ₁ ∴x ₁ = l ₁ /l・d x ₂ = d ₁ −x ₁ = d ₁ −l ₁ /l・d x/x ₁ = d−l ₁ /l・d /l ₁ /l・d=ld
₁ −l ₁ d/l ₁ d = (l/l ₁・d ₁ /d−1) ...(2) Substitute equation (1) into equation (2) i _A /i _B = (l/l ₁・d ₁ /d−1) ……(2)′ ∴l=(i _A /i _B +1)・l ₁ /d ₁・d ……(3) In other words, the distance l is determined by i _A /i _B You can ask for it.

As can be seen from equation (1) or equation (3), the light spot position or distance measurement on the PSD can be obtained by calculating the ratio of the output currents of the detection electrodes of the PSD.

FIG. 4 shows an example of the configuration of the simplest arithmetic circuit.
In the figure, A ₁ , A ₂ , A ₃ are operational amplifiers,
A ₁ and A ₂ are logarithmic compression diodes D ₁ and D ₂ respectively.
is provided in the feedback circuit to form a logarithmic compression amplifier. Electrode A of the PSD is connected to A ₁ , electrode B is connected to A ₂ , and common electrode C is connected to A ₁ and A ₂ . D ₁ and D ₂ use elements with the same characteristics. A feedback resistor and an input resistor of the same resistance value R are connected to the amplifier A ₃ to form each logarithmic compression amplifier.

If the photocurrents from the A and B electrodes of the PSD are i _A and i _B , the output voltages of amplifiers A ₁ , A ₂ , A ₃ are v ₁ , v ₂ and
v ₃ is given by the following equation.

v ₁ = nKT/qlni _A /i _S v ₂ = nKT/qlni _B /i _S …
…(4) ∴v ₃ = v ₂ − v ₁ = nKT/qlni _S /i _B …(5) Here, T: Absolute temperature K: Boltzmann constant q: Electron charge n: Diode D ₁ , D ₂ Constant specific to It does not hold true when In reality, as shown in Fig. 5, the photocurrent from the A and B electrodes includes noise components I _A , in addition to the signal currents i _A and i _B that occur between t ₁ and t ₂ .
Includes _IB . Also, the values of I _A and I _B are completely indeterminate,
There is no correlation with i _A and i _B. In order to solve this problem, the inventor of the present invention changed the outputs v ₁ and v ₂ of amplifiers A ₁ and A ₂ to i _A ,
We have already proposed a circuit that can make i a function of only _B. The circuit involved in this proposal inserts a high pulse filter between the electrodes A and B of the PSD and the logarithmic diodes D ₁ and D ₂ , and also pulses the light emitted from the light emitting element (LED). Only the photocurrent of the PSD due to the reflection of light flows through the diodes D ₁ and D ₂ .
According to this configuration, it is possible to eliminate the influence of background light that does not include high frequency components.

Although not exactly the same as the device proposed by the inventor, for example, the devices disclosed in JP-A-56-29216 (instantaneous light detection circuit) and JP-A-54-121164 (photometric circuit for distance detection device) The inventions have in common the difference in the frequency components of the background light and the signal light, that is, the background light is regarded as a low frequency or direct current, and only the high frequency component, which is the signal light, is amplified by using a capacitor.

The purpose of the present invention is not to focus on the high-frequency components mentioned above, but to provide a feedback circuit with a holding function, set the detection period corresponding to the light emission period, and activate the holding function to more accurately detect background light noise. An object of the present invention is to provide a distance measuring device capable of removing components.

A distance measuring device according to the present invention for achieving the above object will be described below in conjunction with the embodiment shown in FIG.

That is, the distance measuring device according to the present invention includes a light emitting element.
emitting a beam-shaped light pulse from an LED, and focusing the reflected light from an object irradiated with the pulsed light on a PSD located a certain baseline length away from the light emitting element;
A distance measuring device that determines the distance to an object by amplifying the photocurrent obtained from a pair of electrodes of the PSD using a pair of logarithmic amplifiers A ₁ and A ₂ and using a differential amplifier A ₃ to determine the difference in the amplified outputs. and feeding back to each logarithmic amplifier a circuit having a control input terminal and having a function of holding an output current corresponding to the input signal at the time when the control signal is applied while the control signal is being supplied to the control input terminal. circuit gm ₁ ,
gm ₂ , and each of the feedback circuits is connected in synchronization with the optical pulse emission period by the timing circuit 10.
Generate control signals to the control input terminals of gm ₁ and gm ₂ ,
The differential amplifier _A3 is configured to determine the distance to the object during the control signal generation period.

Hereinafter, the apparatus according to the present invention will be explained in more detail with reference to the drawings and the like.

First, the output current waveforms from the A and B electrodes shown in FIG. 5 will be examined in detail. Suppose that a light spot is formed on the PSD from t ₁ to t ₂ due to light reflected from an object due to pulsed LED irradiation. The output current up to time _t1 is clearly all noise components. Between t ₁ and t ₂ , the sum of signal components i _A and i _B due to light emission from the light emitting elements (LEDs) and their respective noise components appears. After t ₂ , there is only noise component again.

FIG. 6 shows an embodiment of the device according to the invention. Components common to those previously explained in FIG. 4 are given the same reference numerals. gm ₁ and gm ₂ in the figure
forms a feedback circuit with a control terminal. The output current and feedback current when no control signal is applied to gm ₁ and gm ₂ have the same value and opposite sign as the PSD output current. i.e.
The photocurrent of the PSD is completely absorbed by gm ₁ and gm ₂ and does not flow into the diodes D ₁ and D ₂ . Also this gm ₁ , gm ₂
As will be described later, when a control signal is input, it has a memory function that allows the output current to continue flowing at the moment the control signal is input, regardless of the input. Then, when a control signal is applied in synchronization with the light emitting element emitting pulsed light toward an object, the output terminals of gm ₁ and gm ₂ will change at that moment.
The photocurrent of the PSD, that is, the state in which the noise components I _A and I _B are maintained is maintained. The increased PSD currents i _A and i _B due to the pulsed light reflected from the object, i.e., the signal components, are transferred to the log diodes D ₁ and D ₂
As a result, the outputs v ₁ and v ₂ of A ₁ and A ₂ are only signal components. That is, voltages v ₁ and v ₂ that depend only on i _A and i _B , which are not affected by external light noise, can be obtained.

Figure 7 shows an example of gm ₁ and gm ₂ . When there is no control signal in the switch circuit S in the figure (L level), the switch is conductive and the capacitor C is charged by the output voltage of the amplifier _A4 . Transistors Q ₂ and Q ₃ are capacitors, said charging voltage (A ₄
output voltage).
When the control signal (H level) is input, the switch S becomes non-conductive, the charging voltage of the capacitor C remains held, and a current corresponding to the time at which it is held is output from the transistor _Q3 .

Then, the output of Q ₃ is connected to each feedback circuit gm ₁ , gm ₂
The output is connected to point A or point B in FIG.

FIG. 8 is a circuit diagram showing an embodiment of an autofocus camera circuit using the above-described device. The same reference numerals are given to the circuit parts described above.

S ₀ is the start switch, and this switch
Turning on S ₀ turns on power to all electrical circuits.
gm ₁ and gm ₂ respectively sink currents equal to the output currents of electrodes A and B of the PSD, and the output voltages of A ₁ , A ₂ , and A ₃ are v ₁ = v ₂ = v ₃ =0. At time t ₁ (see FIG. 5), a control signal is issued from the timing circuit 10 at the same time that the LED emits light. As a result, the output voltages v ₁ and v ₂ of A ₁ and A ₂ take on the values shown in equation (4) above, which correspond to the signal components of the PSD current. The output voltage v ₃ of A ₃ is the voltage difference between v ₁ and v ₂ shown in equation (5). The switch circuit 1 becomes conductive, and the peak value of v ₃ is held in the peak hold circuit 2 and inputted to the next A/D conversion circuit 3. When performing A/D conversion in this A/D conversion circuit 3, a reference voltage proportional to the absolute temperature is used to convert the input voltage shown in equation (5) to the A/D conversion circuit 3.
Convert. As a result, the A/D conversion output is not affected by temperature.

Next, at time _t2 , the control signal disappears, and at the same time, the A/D converted data is latched by the latch circuit 4. On the other hand, the lens drive circuit 8 starts moving the photographing lens of the camera after _t2 in response to the signal passed through the delay circuit 11. As the lens moves, the pulse train generating circuit 7 generates a pulse train corresponding to the lens movement distance. This pulse train and the data previously latched by the latch circuit 4 are matched by the coincidence circuit 5.
When they match, the stop signal circuit 6 generates a signal to stop the lens drive, and stops the movement of the lens.

As described in detail above, according to the present invention, it is possible to measure distances unaffected by external light noise in a distance measuring device. Furthermore, as can be seen from equation (5), since the device according to the present invention uses the ratio of i _A and i _B , distance measurement is possible regardless of the intensity of the light emission pulse.

That is, the removal of the influence of background light in the present invention is different from the inventions of JP-A-56-29216 (instantaneous light detection circuit) and JP-A-54-121164 (photometering circuit for distance detection device). In contrast, high frequency components are not used as signal components.

As mentioned above, a circuit with a holding function is used as a feedback circuit to maintain the noise level and then determine the difference in signal light.

Therefore, instead of detecting only the rising component of the optical pulse, sufficient information can be captured regardless of the frequency component.

Further, it is not affected in any way by pulses having shapes similar to signal components other than the control signal generation period.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the structure of the PSD used in the device according to the present invention, FIG. 2 is an equivalent circuit diagram of the PSD,
Fig. 3 is a layout diagram of the distance measuring device, Fig. 4 is a circuit diagram showing the most basic distance calculation circuit, Fig. 5 is a waveform diagram showing the output current of the PSD, and Fig. 6 is a distance measuring device according to the present invention. 7 is a circuit diagram showing an embodiment of the feedback circuit, and FIG. 8 is a circuit diagram showing an embodiment of an autofocus camera circuit using the distance measuring device. PSD...Non-scanning semiconductor position detection device, A ₁ ,
A ₂ , A ₃ , A ₄ ... operational amplifier, D ₁ , D ₂ ... logarithmic compression diode, gm ₁ , gm ₂ ... feedback circuit.

Claims (1)

[Claims] 1 Emit a beam-shaped light pulse from a light emitting element,
The reflected light from the object irradiated with the pulsed light is imaged on a PSD located a certain baseline length away from the light emitting element, and the photocurrent obtained from each pair of electrodes of the PSD is amplified by a pair of logarithmic amplifiers, and the image is A distance measuring device that determines the distance to an object by determining the difference in width output using a differential amplifier, which has a control input terminal, and has a control signal applied to the control input terminal during a period in which the control signal is supplied to the control input terminal. A circuit having a function of holding an output current corresponding to an input signal at a time is connected to each of the logarithmic amplifiers as a feedback circuit,
A distance measuring device in which a timing circuit generates a control signal to a control input terminal of each of the feedback circuits in synchronization with the optical pulse emission period, and a distance to the object is determined by the differential amplifier during the control signal generation period.