JPH0466283B2 - - 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. 3. 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
5 is a power supply for applying a reverse bias to the PSD. 31 is a current-voltage conversion circuit that converts each of the currents I ₁ and I ₂ generated in electrodes A and B into voltages, and the outputs from this conversion circuit are input to a subtraction circuit 32 and an addition circuit 33, respectively. The outputs of are added and subtracted. 34 is a division circuit which calculates (I ₂ +I ₁ )/(I ₂ −I ₁ ) based on the outputs from the subtraction and addition circuits.

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 is l, R _S is, and the external load resistance is R _L , 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 that applies a reverse bias to the light spot position detector; and a plurality of first switches that switch the output from the anode electrodes; a current-voltage converter that converts the output current from the anode electrode into voltage; a comparator that receives the output from the current-voltage converter as one input; and integrates the output of the comparator by inputting the output. an integrator that supplies its output as the other input of the comparator;
A constant voltage power source input to the non-inverting input side of the current-voltage converter, an output from the constant voltage source input to the comparator by an inverted output that is inverted based on the output of the comparator, and an output from the anode electrode. a second switch that switches the output of the comparator, a binary counter that receives the output of the comparator and inverts the output to a high or low level every fixed count value, and a smoothing circuit that inputs the output of this counter. The present invention is characterized in that the first switch is configured to switch based on the output.

<Example> Fig. 1 is a circuit diagram showing an embodiment of the light spot position detection device of the present invention, and Fig. 2 shows important points (A to D) of Fig. 1.
FIG.

In FIG. 1, the same elements as those in FIG. 3 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 9. That is, the current 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 . 1
0a is an OP amplifier, and a current-voltage converter 1 is connected by the resistor _R5 installed between its output and the inverting input terminal.
Configure 0. The first switch 9 switches the input of currents I ₁ and I ₂ to the inverting or non-inverting input terminal of the OP amplifier 10a. The output of the OP amplifier 10a is input to the non-inverting input terminal side of the comparator 11 via a protective resistor _R6 . Reference numeral 12 denotes an integrator constituted by an OP amplifier 12a and a capacitor _C1 provided between its output side and an inverting terminal. The output of the comparator 11 is input. 13 is a constant voltage source, and this constant voltage source has
One terminal of SW ₁ , SW ₄ , SW ₅ and the non-inverting input terminal of OP amplifiers 10a, 12a are connected. 15 is a binary counter which outputs both high and low level signals based on the output of the comparator 11, and SW ₁ ,
Switch SW ₂ , SW ₃ , and SW ₄ in conjunction. 16 is a resistor _R7 and a capacitor connected to either the high or low output of the binary counter.
It is a smoothing circuit consisting of _C2 .

In the above configuration, now binary counter 1
5's Q output is at low level, the output is at high level, and at that time SW ₁ , SW ₂ and SW ₅ are open, SW ₃
and SW ₄ are assumed to be in the closed state.

The current _I2 generated at the B electrode of the PSD in the above state is
It flows into the constant voltage source 13 through SW ₄ . Meanwhile PSD
The current I ₁ generated at the A electrode passes through SW ₃ and is input to the inverting input terminal side of the OP amplifier 10a. As a result, the output voltage V ₁ of the OP amplifier 10a is V ₁ =V _S −
Since the relationship is IR ₅ , the voltage at point A, the inlet of the inverting input terminal of comparator 11, is the potential V _S shown in Figure 2a.
−I ₁ R ₅ . At this time, the potential at point B is the comparator 11
The constant voltage V _S depends on whether the output is high level or low level.
rises or falls at a constant rate over time. This time is determined by the integration time of the integrator 12, and can be expressed by the following equation.

T ₁ = 2 (C ₁ /I) × (I ₁ R ₅ ) …(4) T ₂ = 2 (C ₁ /I) × (I ₂ R ₅ ) … (5) where I: bidirectional constant Current value of current source In FIG. 2, the potential at point C is at a high level, and the potential at point D is at a low level.

In this example, the potential at point B starts from V _S and falls at a constant rate;
When the voltage drops to V _S -I ₁ R ₅ , the output of the comparator 11 is inverted and the point C becomes a low level. As a result, the output of the inverter 18 is inverted and the second switch 20
becomes closed and the potential at point A becomes V _S. At the same time, the potential at point B increases at a constant rate, and at the moment it becomes the same as the potential at point A (V _S ), the output of comparator 11 becomes high level and the output Q of binary counter 15
is a high level and is a low level. the result,
SW ₁ and SW ₂ are closed, and SW ₄ and SW ₄ are open.

In the above state, the current I ₁ generated at the A electrode of the PSD flows into the constant voltage source V _S , and the current I ₂ generated at the B electrode is input to the inverting input terminal of the current-voltage converter 10. Thereafter, the same operation as described above is repeated, and the operation returns to the beginning. The output of the binary counter in such a repetitive operation is shown in FIG. 2d. Here, if the high level potential at point D is +E and the low level potential is -E, the output V _put after passing through the smoothing circuit 16 is V _put = (-ET ₁ + ET ₂ ) / (T ₁ + T ₂ ) = E (T ₂ −T ₁ )/(T ₁ +T ₂ ) Substituting equations (4) and (5) into the above equation, V _put = (2EC ₁ R ₅ /I) ・(I ₂ −I ₁ )/( I ₁ + I ₂ ) ∝ (I ₁ − I ₂ )/(I ₁ + I ₂ ) …(6).

According to formula (6), the difference between the sums of currents I ₁ and I ₂ is calculated, and according to formula (3) shown in the conventional example, displacement x
can be detected.

<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 improve high precision and high reliability.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the PSD of the present invention, Fig. 2 is a waveform diagram showing the waveforms of the main parts of Fig. 1,
FIG. 3 is a circuit diagram of a conventional PSD. 9... First switch, 10... Current-voltage converter, 11... Comparator, 12... Integrator, 13... Constant voltage source, 14... Bidirectional current source, 15... Binary counter, 16... Smoothing circuit, 20 ...Second switch,
30...Light spot position detector.

Claims (1)

[Claims] 1 two anode electrodes A separated by a predetermined distance,
B, a light spot position detector 30 that outputs two electrical signals having different intensities depending on the incident position of the light, a constant voltage source 35 that applies a reverse bias to this light spot position detector, and the anode electrode. a first switch 9 for switching the output from the anode electrode, and a current-voltage converter 10 for converting the output current from the anode electrode into a voltage.
, a comparator 11 whose one input is the output from this current-voltage converter, and an integrator 12 which inputs and integrates the output of this comparator and supplies the output as the other input of the comparator. and a constant voltage source 13 input to this integrator and the current-voltage converter.
and a second switch 20 which switches between the output from the constant voltage source 13 and the output from the anode electrode which are input to the comparator with an inverted output that is inverted based on the output of the comparator; It consists of a binary counter 15 whose output is inverted to a high or low level at every fixed count value, and a smoothing circuit 16 which receives the output of this counter and outputs an electrical signal corresponding to the displacement of the incident position of the light,
A light spot position detection device characterized in that the first switch is configured to switch based on the output of the counter.