JPH0466282B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is directed to a semiconductor light spot position detector (Position Sensitive) using, for example, a photodiode.
The present invention relates to a light spot position detection device using a device (hereinafter referred to as PSD), and more specifically relates to improvement of a position detection circuit.

<Prior Art> Conventionally, as a PSD detection circuit, a circuit described in the magazine Optronics No. 39 (published in March 1985) is known.

The configuration of the detection circuit of the light spot position detection device described in the magazine will be explained using FIG. 4. In the figure, numeral 30 is a PSD, and the p-layer on the surface has a high specific resistance and acts as a resistance layer. The i-layer is a high-resistance n-layer, and by expanding a depletion layer in this region, high sensitivity and high-speed response are achieved. A and B are two anode electrodes connected to both ends of the p layer,
3 and 5 are power supplies for applying reverse bias to the PSD. 31 is the current I ₁ generated in electrodes A and B,
This is a current-voltage conversion circuit that converts each of I ₂ into a voltage, and the outputs from this conversion circuit are input to a subtraction circuit 32 and an addition circuit 33, respectively, and the outputs are added and subtracted. 34 is a division circuit,
Based on the output from the subtraction and addition circuits, (I ₂ +
Calculate I ₁ )/(I ₂ − I ₁ ).

Here, the principle of PSD will be briefly explained. PSD
Among the electron-hole pairs generated when the surface of 30 is irradiated with light, the carriers that reach the junction are divided by the p layer in inverse proportion to the incident position of the light and the distance to the two anode electrodes. taken out from each electrode. The incident position of light can be calculated from the current value. Now, if light is incident on point Q, carriers generated in the semiconductor will drift due to the electric field in the depletion layer, resulting in a generated current I ₀ , and holes will be
layer, electrons reach the n layer. Resistances R ₁ and R ₂ from point Q to electrodes A and B are respectively
and is proportional to the distance to B. Therefore, the holes injected into the p-layer are divided by the resistors R ₁ and R ₂ and generated currents I ₁ and I ₂ flow to the electrodes A and B.

If the distance from the midpoint of electrodes A and B to point Q is x, the distance and resistance between electrodes A and B are l and R _S , and the external load resistance is R _L , then I ₁ and I ₂ are respectively expressed by the following equations. It can be expressed.

I ₁ = {R _S /2 (1-2x/l) + R _L / (R _S +2/R _L )}・I ₀ …(1) I ₂ = {R _S /2 (1+2x/l) + R _L / (R _S +2/R _L )}・I ₀ (2) During actual measurement, I ₀ is not constant because of variations in the output light of the light source and changes in the distance between the light source and the light spot position detector. Therefore, by taking the ratio of the difference and the sum of the output currents and normalizing it by _I0 , it becomes a function of only x as shown in the following equation.

(I ₂ - I ₁ ) / (I ₂ + I ₁ ) = R _S / (R _S + 2R _L )・2x/l...(3) <Problems to be solved by the invention> By the way, in the configuration of the above conventional example, Each of the current outputs I ₁ and I ₂ from the electrodes A and B is converted into a voltage using two current-voltage conversion circuits, and based on the outputs from the two conversion circuits, a subtraction circuit 32 calculates (I ₂
−I ₁ ) and (I ₂ +I ₁ ) in the adder circuit 33, and these outputs are calculated in the divider circuit 34 as (I ₂ +I ₁ )/
The calculation (I ₂ − I ₁ ) is being performed.

Since three stages of conversion or calculation are performed in this way, errors at each stage are accumulated and accuracy deteriorates.

The circuit becomes complicated and the cost increases.

There is a problem.

The present invention was made in view of the above problems, and
By calculating the difference between sums with a simple configuration,
The aim is to provide a small, high-precision, and low-cost PSD.

<Means for solving the problems> The configuration of the present invention for solving the above problems is as follows:
a light spot position detector having two anode electrodes separated by a predetermined distance; a power source for applying a reverse bias to the light spot position detector; a first switch for switching the output from the anode electrode; An integrator that inputs the output from the anode electrode, and a second integrator provided between the output terminal and the inverting input terminal of this integrator.
and a first switch that inputs the output of the integrator.
an inverter, a counter to which the output of this inverter is input and whose output is inverted to a high or low level at every fixed count value, a smoothing circuit to which the output of this counter is input, and a second inverter, the first inverter The second switch is switched by the output of the counter, and the first counter is switched by the output of the counter.

<Embodiment> FIG. 1 is a circuit diagram showing an embodiment of the light spot position detection device of the present invention.

In FIG. 1, the same elements as those in FIG. 4 are given the same reference numerals and their explanations will be omitted. In the present invention, the outputs from electrodes A and B of the PSD are input to the first switch 10. That is, the output I ₁ from electrode A is connected to interlocking changeover switches SW ₁ and SW ₂ , and the output I ₂ from electrode B is connected to interlocking switches SW ₃ and SW ₄ .
11a is an OP amplifier, and the integrator 11 is connected to the output of the OP amplifier and the capacitor _C1 installed between the inverting input terminal.
Configure. The first switch 10 switches the input of currents I ₁ and I ₂ to the inverting or non-inverting input terminal of the OP amplifier 11a. A second switch _SW5 is connected to the OP amplifier 11a in parallel with the capacitor _C1 , and a constant voltage source 16 is connected to the non-inverting input terminal.
is connected. The output of the OP amplifier 11a is input to a first inverter 12, and the output of this inverter 12 is input to a counter 13 whose output is inverted to a high or low level at every fixed count value, and is also input to a second switch _SW5 . It has been entered. The output of the counter 13 is input to a smoothing circuit 14 consisting of second switches SW ₁ , SW ₂ , a second inverter 15, a resistor R ₁ , and a capacitor C ₂ .
The output of the inverter 15 is input to SW ₃ and SW ₄ .

In the above configuration, the outputs of the first and second inverters and the counter 13 are now at a low level, SW ₁ , SW ₂ and SW ₅ are open, and SW ₃ is open.
and SW ₄ are assumed to be in the closed state. In the above condition
The current I ₂ generated at the B electrode of the PSD flows into the constant voltage source 16 through SW ₄ . On the other hand, the current I ₁ generated at the A electrode of the PSD passes through SW ₃ and is input to the inverting input terminal side of the OP amplifier 11a. The output voltage V ₁ of the OP amplifier 11a drops from a potential equal to the voltage of the constant voltage source V _S in proportion to the time T ₁ and the current value I ₁ and inversely proportional to the capacitance of the capacitor C ₁ . That is, V ₁ =V _S −(T ₁ ·I ₁ /C) (4).

When the output voltage V ₁ of the OP amplifier 11a reaches the threshold voltage (V _Io ) of the first inverter 12, the output of the first inverter 12 is inverted from low level to high level, and the count number of the counter 13 is increased. Increase by one. At this time, the second switch SW ₅
becomes closed and shorts the capacitance of capacitor _C1 . As a result, the output V ₁ of the OP amplifier 11a instantly becomes equal to the voltage V _S of the constant voltage source 16, the output of the first inverter also instantaneously inverts from high level to low level, and SW ₅ becomes open again. Become.

The above operation is repeated and when the count number of the counter 13 reaches the set value, the output level of the counter is inverted to high level. As a result, SW ₁ and SW ₂ are closed, the output of the second inverter 15 is inverted to high level, and SW ₃ and SW ₄ are opened.

In the above state, the current I ₁ generated in the A electrode of the PSD
flows into the constant current source V _S through SW ₁ , and also flows into B
The current _I2 generated in the electrode passes through _SW2 and goes to OP amplifier 1.
Input to the inverting input terminal side of 1a. At this time
The output voltage V ₁ of the OP amplifier 11a is V ₁ =V _S −(T ₂ ·I ₂ /C) (5).

After that, the switching operation as described above is repeated until the count number of the counter reaches the set value.
Return to initial operation.

FIGS. 2a, b, and c are diagrams showing waveforms of the output of the OP amplifier 11a, the output of the first inverter 12, and the output of the counter 13 in FIG.
In addition, in this embodiment, the setting value of the counter is shown as being set to 4. According to these figures, the current of I ₁ is input to the OP amplifier 11a, and the current of T ₁
It can be seen that the output of the first inverter 12 momentarily inverts with a time constant of , and that the output of the counter 13 inverts every four times the output of this inverter inverts.

Here, the threshold voltage V _Io of the first inverter 12 is V _Io = V _S − (T ₁ · I ₁ /C) (6) Similarly, V _Io = V _S − (T ₂ · I ₂ /C) ...(7) From equation (6), T ₁ = C(V _S −V _Io )/I ₁ ...(8) Similarly, T ₂ = C(V _S −V _Io ) /I ₂ ...(9).

Analog output by smoothing the output of counter 13
V _put is as follows: V _put = (-E・nT ₁ +E・nT ₂ ) / (nT ₁ +nT ₂ ) = (T ₂ −T ₁ )/(T ₁ +T ₂ )・E (10) (This example Then n=4). Substituting equations (8) and (9) into equation (10), we get V _put = (1/I ₂ - 1/I ₁ ) / (1/I ₂ + 1/I ₁ )・E = (I ₁ - I ₂ )/(I ₁ + I ₂ )・E...(11) According to equation (11), the difference between the sums of currents I ₁ and I ₂ is calculated, and since E = constant, conventional The displacement x can be detected using equation (3) shown in the example.

Note that in this embodiment, the second inverter 1
5 was used for switching between SW ₃ and SW ₄ , but it may also be provided on the SW ₁ and SW ₂ sides with the inverted polarity reversed. Further, the set value n of the counter can be changed as necessary.

Figure 3 shows another embodiment of the light spot position detector in which two commonly used photodiodes are installed close to each other.The beam diameter is relatively large and the light straddles these photodiodes. It can be used in cases where you are moving with a bump.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, high precision and expensive parts are not required, the circuit configuration is simplified, and the number of parts is small, so costs can be reduced. It can be realized.

Compared to the conventional example, calculation errors are not accumulated, so the accuracy is high.

Suitable for C-MOS IC manufacturing process, 1
Since it is suitable for chip IC implementation, it is possible to achieve high precision and high reliability.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the light spot position detection device of the present invention, FIG. 2 is a waveform diagram showing the waveforms of the main part of FIG. 1, and FIG. 3 is a diagram showing another embodiment. FIG. 4 is a circuit diagram of a conventional light spot position detection device. 10...first switch, 11...integrator, 12...
1st inverter, 13... Counter, 14... Smoothing circuit, 30... Light spot position detector (PSD), A, B...
Anode electrode, SW ₅ ...Second switch.

Claims (1)

[Claims] 1 two anode electrodes A separated by a predetermined distance,
A light spot position detector 30 that has an electric field B and outputs an electric signal whose intensity varies depending on the incident position of light, and a constant voltage source 35 that applies a reverse bias to this light spot position detector.
and a first switch for switching the output from the anode electrode.
a switch 10, an integrator 11 inputting the output from the anode electrode, and a second switch SW ₅ provided between the output terminal and the input terminal of this integrator.
a first inverter 12 to which the output of the integrator is input, a counter 13 to which the output of this inverter is input and whose output is inverted to high or low level at every fixed count value; It consists of a smoothing circuit 14 that outputs an electric signal corresponding to a change in the incident position of light, and a second inverter 15.The output of the first inverter switches the second switch, and the output of the counter switches the second switch. A light spot position detection device characterized in that it is configured to perform switching of a first switch.