JPH0245703A - Optical position detecting device - Google Patents

Abstract

PURPOSE:To detect a high-accuracy light position signal by providing specific stages of amplifiers which amplify the sum of and the difference between output signals of optical position detecting elements with a specific gain and selecting the best stage of an amplifier according to respective signals which are given the gain. CONSTITUTION:Analog switches 62-66 are connected to the output sides of the N states of the amplifiers 46-49 which amplify the signal of a difference from a differential amplifier 39 and the input signal of the front stage with the gain A. Further, the respective outputs of N stage of amplifiers 42-45 which amplify the signal of a sum inputted from an adding circuit 38 and the input signal of the front stage are compared by comparators 50-54 with a slice level SL. Then the comparison results of the comparators 50-54 are inputted to a priority encoder 55 with priority level and converted into digital values according to the predetermined priority level and a demultiplexer 56 turns on only corresponding signals, thereby turning on the best pair of the signals of the sum and difference among the analog switches 57-66.

Description

[Detailed Description of the Invention] [Table of Contents] Overview Industrial Application Fields Conventional Technology Problems to be Solved by the Invention Means for Solving the Problems Action Embodiment One Embodiment of the Present Invention Effects of the Invention (Chapter 5.6) (Figures 1 to 4) [Summary] Regarding optical position detection devices, the purpose of this invention is to provide optical position detection devices that can detect highly accurate optical position signals at high speed and a wide dynamic range. a photodetecting means for photoelectrically converting the light and dividing and outputting the photocurrent from a predetermined electrode, which is shunted through a predetermined resistance layer; and an arithmetic means for calculating the sum and difference of each output signal taken out from the electrode. , and a light position detection means for detecting the incident position of light based on the ratio of the sum and difference calculated by the calculation means, wherein the sum and the difference are connected to the output side of the calculation means. a predetermined stage of amplifiers that amplify the sum with a predetermined gain; a selection means that selects the amplifier that provides the optimum gain for the sum and the difference based on the output of each stage of the amplifier that amplifies the sum; and the selection means switching means for switching the amplifier so as to give the same gain to both the sum and the difference based on the output of the amplifier.

1' Industrial Application Field] The present invention relates to an optical position detection device, and more specifically, to an optical position detection device (PSD: Po5ition 5ensit).
ive Detector (hereinafter abbreviated as PSD).

A PSD is a device with a pin structure that utilizes the effect that photocurrent flowing through a semiconductor is shunted through a surface resistance layer. Electrical signal (X
-Y coordinate signal) and has excellent positional resolution and responsiveness. Therefore, it can be applied to automatic focusing devices such as cameras, various distance measuring devices, positioning devices, etc.

[Conventional technology]

FIG. 5 is a sectional view showing the structure of a one-dimensional PSD. In this figure, 1 is PSD, PSDI has a p-type resistor N2 on the surface of the silicon plate, and 1-
It is composed of 3i layers and 403 layers, and output terminals 5 and 6 are formed on both sides of the P-type resistance layer 2, and a common terminal 7 is formed on the n' layer 3, respectively. It is assumed that a predetermined bias voltage is applied between the output terminal 5.6 and the common terminal 7, and a light spot is irradiated to the X point. The midpoint of the sample is taken as the origin of the coordinates, and the length of the sample is 2L.

When a light spot is incident on the PSDI, a charge proportional to the light energy is generated at the incident position, and the generated charge passes through the resistance layer (P layer in this case) as a photocurrent and is output from the electrode. The resistance layer is formed to have a uniform resistance value over the entire surface, and the photocurrent is divided and extracted in inverse proportion to the distance (resistance value) to the electrode. Here, the distance between the electrodes is 2L, and the photocurrent is ■. Then, the current taken out from the output terminal 5.6 is 1. ．． 1. is expressed by the following equation (2), and the light position and light position are expressed by the following equations (2) and (2), respectively.

Light intensity -II +x, ......■Figure 6 is PS
2 is a diagram showing a signal processing circuit for signal processing the output current Il, 2 of the DI to obtain an optical position signal. FIG. In this figure, 11 is a signal processing circuit, and OP amplifiers 12 to 1
6, capacitors C1, C2, resistors Rf +, Rf z
, R+-Rq and an analog divider 17. OP amplifier 12.13, capacitor C8, Ct and resistor Rf.

, Rf constitute a current-voltage conversion circuit 18, and the OP amplifier 14 and resistors R, , R, , R5 constitute an adder circuit 19. In addition, the OP amplifier 15 and resistors R3, R4,
R6 and Rf constitute a differential circuit 20, and the OP amplifier 16 and resistors Rs and Rq constitute an inverting circuit 21. Therefore, the conventional signal processing circuit 11' has two PSDI current outputs 1. , I are converted into voltages by a current-voltage conversion circuit 18, a sum and a difference are created by an adder circuit 19 and a differential circuit 20, and a position signal is obtained by an analog divider 17.

[Problem to be solved by the invention]

However, such conventional optical position detection devices have the following problems.

■ The dynamic range of light intensity is small.

When the brightness of light itself changes, the ratio of the maximum value to the minimum value that can be handled is called the dynamic range, and this is approximately 10
It's double. As will be described later, this is a problem with the signal processing circuit rather than with the PSD itself.

■ The operating speed is slow, approximately IMHz.

■ Poor accuracy. In some cases, the error is 10% or more.

The cause of these shortcomings is not in the PSD itself, but in the fact that an analog division circuit (see analog divider 17 shown in FIG. 6) is used during division when extracting as an optical position signal. In general, analog division circuits have slow operating speed, small dynamic range, and poor accuracy, but because they can easily perform division with a single IC (no other circuit can perform division with a single IC), they are suitable for PSD. is widely used.

In order to eliminate the above-mentioned problems, there is a system in which the sum and difference, which are analog signals, are converted into digital signals using an A/D converter and the digital division circuit is used to perform the conversion (Japanese Patent Application No. 61-301718). However, in this case, the A/D converter becomes the bottleneck. If you use an A/D converter with high resolution and high speed, the accuracy will increase accordingly, but since the speed and resolution of an A/D converter have an inverse relationship, the current A/D converter is, for example, 12 bits.
The resolution is I MHz, and the limit is about 20 MHz with 10 bits. At this time, the problem is the optical dynamic range, and even if the division is done digitally, the dynamic range cannot be large. In other words, when the denominator voltage becomes small, the effective b of the data after A/D conversion
For example, if the denominator is 12 bits and a speed of IMHz is required, the maximum accuracy is limited to about 12 bits. The resolution was set to 12 bits (the molecule is also 12 bits).
For example, if the brightness changes by a factor of 10, the resolution will drop from a full 12 bits to the equivalent of 8 bits. Furthermore, if the magnitude changes by 16 times, in the worst case, only 8 bits of accuracy can be obtained, and even if a 12-bit A/D converter is used, the accuracy will be 8 bits/8.
This means that an accuracy of a little less than 8 bits can be obtained at most.

In this way, among the light positions expressed as numerator (difference)/denominator (sum), accuracy cannot be improved if the size of the denominator itself changes significantly.

PSD is used to find the position of light, but depending on the object, it may measure things whose brightness changes with the position, and since the denominator is proportional to the brightness (light power of the light), the amount of light changes as well. When the position also changes, there is a desire for something that can detect the light position without depending on the amount of light.

In addition, in camera autofocus, etc., such MH
! Although precision on the order of magnitude is not required, current methods are insufficient when applied to very high precision and high performance measurement equipment.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical position detection device capable of detecting highly accurate optical position signals at high speed and over a wide dynamic range.

[Means to solve the problem]

In order to achieve the above object, the optical position detection device according to the present invention includes a photodetecting means that photoelectrically converts incident light and divides and outputs a photocurrent to be shunted through a predetermined resistance layer from a predetermined electrode, An optical position detection device comprising a calculation means for calculating the sum and difference of each output signal, and an optical position detection means for detecting the incident position of light based on the ratio of the sum and difference calculated by the calculation means. Then, on the output side of the arithmetic means, there is provided a predetermined stage of amplifier that amplifies the sum and difference with a predetermined gain, and an amplifier that is optimal for the sum and difference based on the output of each stage of the amplifier that amplifies the sum. and a switching means for switching the amplifier so as to give the same gain to both the sum and the difference based on the output of the selection means.

[Effect]

In the present invention, predetermined stages of amplifiers are provided to amplify the sum and difference of two output signals of the PSD with a predetermined gain, and an optimal stage of amplifier is selected based on each gain-applied signal. The amplifier is then selected to provide the same gain for both the sum and difference.

Therefore, since the same gain is given to both the sum and difference represented as the denominator and numerator, the dynamic range of the denominator (light intensity) can be greatly improved without affecting the result of division. Accurate optical position signals can be obtained.

(Example〕 Hereinafter, the present invention will be explained based on the drawings.

1 to 4 are diagrams showing an embodiment of the optical position detection device according to the present invention. First, the configuration will be explained.

Figure 1 shows an arithmetic circuit that calculates the sum and difference between two output signals of a PSD, and has the same function as the conventional example shown in Figure 6, and the same components are designated by the same numbers. It is attached. In FIG. 1, 31 is an arithmetic circuit (arithmetic means);
2 is an A/D converter, and the arithmetic circuit 31 is composed of OP amplifiers 33 to 36 and resistors R8 to R19. OP amp 33.34 and Ro, Rtz are PSD
1 output current 1. ,I.

A current-voltage conversion circuit 37 is configured to convert O into a voltage.
P amplifier 35 and resistors R13 to RIS are added to adder circuit 38
The OP amplifier 36 and the resistors R16 to RI9 constitute a differential circuit 39, and the outputs of the adder circuit 38 and the differential circuit 39 are the sum (v+ +V2) and the difference (V+ Vz), respectively.
) is output to the signal processing circuit 41 shown in FIG. In addition, in this embodiment, the sum signal is converted into an A/D converter 32 to obtain a digitalized light intensity signal.
is converting.

In FIG. 2, numeral 41 denotes a signal processing circuit, and the signal processing circuit 41 is composed of each element described below. That is, the signal processing circuit 41 has N stages of amplifiers 42 to 45 that amplify the sum (original signal) inputted from the adder circuit 38 and the previous stage input signal with a gain A, and the difference (V+Vz) is inputted to the amplifier 42. - N-stage amplifier 4 that amplifies the difference (original signal) and the previous stage input signal with gain A as in 45.
6 to 49, the sum and each output of the amplifiers 42 to 45 are manually input, and the sum and each output are set to a predetermined slice level SL.
Comparators 50 to 54 and comparator 5
0 to 54 outputs 0 to N are input, the highest input "L" among the 200 to N data is detected, and the value is set to 3.
A priority encoder 55 that encodes the data into a bit code, a demultiplexer 56 that redistributes the prioritized data of the priority encoder 55 to O-H data, and is connected to each output side of the sum and amplifiers 42 to 45. , analog switches 57 to 61 which turn on the optimum one according to the selection signal from the demultiplexer 56 and output it as a sum after level conversion, and analog switches 57 to 61 which are connected to the output sides of the difference and amplifiers 46 to 49 and which are connected to the output sides of the difference and amplifiers 46 to 49, It is constituted by analog switches 62 to 66 that turn on the optimum one according to a selection signal and output it as a difference after level conversion.

Therefore, when N stages of amplifiers with a gain of A (for example, 4 stages of amplifiers with a gain of 10 times) are connected to the sum signal (denominator), the difference signal (numerator) also has the same gain of 10 as the sum signal.
Connect 4 stages of double amplifier and analog switch 57 to 66
By switching , a pair of amplifiers 42 to 49 having the same gain in the denominator and numerator are simultaneously selected.

The amplifiers 42 to 49 constitute an amplifier 67, the comparators 50 to 54, the priority encoder 55 and the demultiplexer 56 collectively constitute a selection circuit (selection means) 6B, and the analog switches 57 to 66 constitute a switching means 69. ing.

The sum and difference after level conversion are manually input to the A/D converters 70 and 71 shown in Fig. 3, and the A/D converters 70 and 71 convert the sum and difference analog signals into digital signals and then convert them into digital signals. It is output to the division circuit (optical position detection means) 72. The digital division circuit 72 outputs the difference (numerator) divided by the sum (denominator) as a position (height) signal to the outside.

Next, the effect will be explained.

As shown in FIG. 4, the gain A of amplifiers 42 to 49 is set to 1.
0 times, the number of stages N of amplifiers 42 to 49 is 4 stages, the slice level SL is 1■, the saturation voltage of amplifiers 42 to 49 is 15V, and the input voltage range of A/D converter 70.71 is ±IOV. .

Now, assuming that there is an input signal of 5■ as a sum signal (denominator voltage), the input signal of all comparators including the ×1 comparator (comparator 50) in comparators 50 to 54 is the reference voltage (slice level 5L)
Since it is larger than IV, all "H" is output to the bryotin coder 55. Also, when the sum signal is 0.5■, only the comparator 5o is "L°", and the remaining comparators 5o
1 to 54 are “H” and the sum signal is 0.05V.
Then, the comparators 50 and 51 become "L", and the remaining comparators 52 to 54 become "H11" (see table).

(This page, margins below).

The comparison results of the comparators 50 to 54 are inputted to a priority encoder 55 with priorities, and are 0.1.2, . . . according to predetermined priorities as shown in the table.
. . ., the demultiplexer 56 turns on only the corresponding signal, and the denominator and numerator of the analog switches 57 to 66 are turned on in pairs.

That is, the selection circuit 68 selects the pair of amplifiers 42 to 46 that have the optimum gain so that the value of the denominator voltage falls within a certain range.

Therefore, a signal with AI gain applied to both the denominator and numerator is A/D converted, and since the gains of the denominator and numerator are equal, the result of division is correct. In addition, the dynamic range of the denominator (light intensity) is ANl (l in this example).
04), which is much larger than the conventional circuit shown in FIG.

As a result, it is possible to obtain a highly accurate optical position signal at high speed (1 MHz) and wide dynamic range (10') relative to the PSD.

In this example, the gain per stage is set to 10 times, but it is set appropriately depending on the desired accuracy. For example, if 8-bit accuracy is desired, the A/D converter is 12 bits and the IM speed is set to 10 times. If desired, an amplifier with a gain of about 16 times (actually about 10 times taking margin into consideration) is selected.

〔effect〕

According to the present invention, a highly accurate optical position signal can be detected at high speed and over a wide dynamic range.

[Brief explanation of the drawing]

Figures 1 to 4 are diagrams showing an embodiment of the optical position detection device according to the present invention, Figures 1 to 3 are its overall configuration diagram, and Figure 4 shows the original signal of the sum signal and the selected output. 5.6 is a diagram showing the conventional optical position detection device, FIG. 5 is a sectional view showing the structure of the PSD, and FIG. 6 is a diagram showing the signal processing circuit. 1...PSD (photodetection means), 5.6...
...Output terminal (electrode), 31... Arithmetic circuit (
calculation means), 32.70.71...A/D converter, 37...current-voltage conversion circuit, 38.
...Addition circuit, 39...Differential circuit, 41...Signal processing circuit, 42-49...Amplifier, 50-54... Comparator, 55...
・Priority encoder, 56...Demultiplexer, 57-66...Analog switch Sochi, 67...
...Amplifier, 68...Selection circuit (selection means), 69...
...Switching means, 72...Digital division circuit. Agent Patent Attorney Igata ＼′ ＼ Disaster Case ■Overall Structure゛Figure 3Figure 3

Claims (1)

[Scope of Claims] Photodetection means that photoelectrically converts incident light and divides and outputs photocurrent from predetermined electrodes to shunt through predetermined resistance layers, and detects the sum and difference of each output signal taken out from the electrodes. In an optical position detection device comprising a calculating means for calculating, and a light position detecting means for detecting a light incident position based on a ratio of a sum and a difference calculated by the calculating means, on the output side of the calculating means, A selection means for selecting a predetermined stage of amplifiers that amplify the sum and difference with a predetermined gain, and an amplifier that provides an optimal gain for the sum and difference based on the output of each stage of the amplifier that amplifies the sum. An optical position detection device comprising: a switching means for switching the amplifier so as to give the same gain to both the sum and the difference based on the output of the selection means.