JP2002022497A - Optical encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an encoder of a constitution in which offset and distortion in waveforms hardly occur in encoder signals and which is capable of drawing out the best of its performance. SOLUTION: The optical encoder of one mode comprises a light source to emit a light beam, a scale which is displaced in such a way as to relatively traverse the light beam and in which an optical pattern of a predetermined period is formed in an region to be irradiated with the light beam, and a light receiving array to receive the light beam via the scale. The light receiving array laminates a first conduction semiconductor layer, a second conduction semiconductor layer, and a first conduction semiconductor layer in this order from the side of a substrate to the side of a light receiving surface A reverse- bias voltage is impressed on the first conduction semiconductor layer on the side of the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical encoder, and more particularly, to an optical encoder used for detecting a moving amount of a movable portion of a device.

[0002]

2. Description of the Related Art Conventional optical encoders include an encoder of a type in which individual components such as a semiconductor laser light source, a photodetector, a diffraction grating, and a collimator lens are combined with high accuracy, and a scale corresponding to a diffraction grating are excluded. There is an encoder of a type in which a portion is miniaturized by a semiconductor process or a bonding technique.

As a conventional example of such an optical encoder, there is "Micro Encoder Using Surface Emitting Semiconductor Laser" by Eiji Yamamoto in "Optics", Vol. 27, No. 6, pages 327 to 328.

FIG. 5A shows the configuration of an optical encoder according to this conventional example.

In FIG. 5A, the basic structure of a micro encoder is a light receiving element 1 composed of a photodiode (PD) integrally formed on a base (silicon substrate) 1.
a, a signal processing circuit 1b, a surface emitting laser 2 bonded to a silicon substrate 1, and a scale in which two types of patterns having a constant reflectance and a difference in reflectance are arranged so as to be relatively movable with respect to the silicon substrate 1. Consists of four.

The light beam emitted from the surface emitting laser 2 enters the scale 4.

By detecting the intensity of the reflected light from the scale 4 with the light receiving element 1a, the relative movement amount between the silicon substrate 1 and the scale 4 can be measured.

Next, in addition to the outline of the configuration of the optical encoder according to the conventional example described above, the structure of a general photodetector used as a light receiving element will be described.

The structure of this photodetector is described in many books on electronic circuits, such as "Example exercise electronic circuit" by Hiroshi Ozaki.

FIG. 5B shows a sectional structure of a PD which is a general photodetector (light receiving element).

The structure of the PD is such that the p-type semiconductor layer 301, the n-type semiconductor layer 302, and the electrodes 301a and the electrodes 301a provided on the n-type semiconductor layer 302a.

Each of the semiconductor layers 301 and 302 contains silicon (Si) as a main component, and is doped with a p-type or n-type dopant.

The p-type semiconductor layer 301 has a thickness of several μm to several tens μm.
And the thickness of the p-type semiconductor layer 302 as a substrate is several hundred μm.

The electrode 302a is connected to an electrical ground, and a negative (-) voltage is applied to the electrode 301a.

This configuration can be changed to another configuration as described below.

(Alternative Configuration 1) The n-type semiconductor layer 301, the p-type semiconductor layer 302, and the electrodes 301a and 301a provided on the n-type semiconductor layer 301 and the p-type semiconductor layer 302, respectively, from the upper side on the light receiving surface side. 302a.

The electrode 302a is connected to an electric ground, and a positive (+) voltage is applied to the electrode 301a.

(Alternative Configuration 2) The metal layer 301, the n-type semiconductor layer 302, and the metal layer 301,
Electrodes 301 provided on each of n-type semiconductor layers 302
a, electrode 302a.

However, as the metal layer 301, a metal layer having a rectifying action with the n-type semiconductor layer 302 is selected.

The electrode 302a is connected to an electrical ground, and a negative (-) voltage is applied to the electrode 301a.

FIG. 5 (c) shows an example of an arrayed light receiving section.

This is disclosed in Japanese Patent Application No. 11-362941 filed by the same applicant as the present invention.

[0023]

As encoders of this type have become smaller and have higher resolution, encoders are being used in a wide range of fields such as machine tools, information equipment, and medical equipment.

Most of the signal processing of the encoder which requires such high precision uses analog signals.

There are two main types of output signals:

(1) Two sine waves different in phase by 90 ° (2) Triangular waves different in phase by 90 ° When this type of encoder performs high-accuracy position detection using analog signals, one cycle And the number 1
It is divided into about 0 to several hundreds.

As described above, in this type of encoder, position detection is performed using an analog signal up to the performance limit.

Therefore, riding on these analog signals,
Waveform distortion and offset due to crosstalk and the like in a plurality of signal sources are factors that degrade the position detection accuracy of the encoder.

As a specific example of crosstalk, an encoder having an array-like light receiving section having a structure as shown in FIG. 5B will be described.

In FIG. 5B, holes generated in the n-type semiconductor layer 302 correspond to the n-type semiconductor layer 30 serving as a substrate.
2, and is drawn to the electrode 301a in one of the elements of the light receiving array unit.

In this case, if the light that has reached the p-type semiconductor layer 302 is diffused and detected by another element of the light receiving array unit that should not be detected, crosstalk is caused.

Next, an example of the offset will be described.

In FIG. 5C, part of the light emitted around the light receiving array portion propagates to the lower layer portion.

Holes generated by the absorption of light in the lower layer are diffused, and some of the holes propagate from the outer periphery of the light receiving array to the inside and are detected.

This is an offset in light detection.

At this time, since the array elements at both ends of the light receiving array portion have a large boundary portion with the outer peripheral portion, they are particularly susceptible to the diffusion of holes, and a large offset is likely to occur in light detection.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an encoder having a configuration in which an offset or a waveform distortion is unlikely to occur in an encoder signal, and which is capable of maximizing performance.

[0038]

According to the present invention, in order to solve the above-mentioned problems, (1) a light source section for emitting a light beam, and a light source section which is displaced so as to relatively cross the light beam, Has a scale in which an optical pattern of a predetermined period is formed in an area to be irradiated, and a light receiving array portion that receives the light beam passing through the scale, wherein the light receiving array portion extends from the substrate side to the light receiving surface side. A semiconductor layer of the first conductivity type, a semiconductor layer of the second conductivity type, and a semiconductor layer of the first conductivity type in this order, and a reverse bias voltage is applied to the semiconductor layer of the first conductivity type on the substrate side. An optical encoder is provided.

(Corresponding Embodiment of the Invention) The first embodiment corresponds to this.

According to the present invention, in order to solve the above problems, (2) a light source unit for emitting a light beam is displaced so as to relatively cross the light beam, and the light beam is irradiated. A scale in which an optical pattern of a predetermined period is formed in a region, and a light receiving array unit that receives the light beam passing through the scale, wherein the light receiving array unit is
A semiconductor layer of the first conductivity type in order from the substrate side to the light receiving surface side,
A semiconductor layer of a second conductivity type, a metal layer having a rectifying action on the semiconductor layer of the second conductivity type, and a reverse bias voltage is applied to the semiconductor layer of the first conductivity type on the substrate side. An optical encoder is provided.

(Corresponding Embodiment of the Invention) Another configuration 2 or 3 of the first embodiment corresponds.

In the above (1) and (2), the first
If the conductivity type is p-type, the second conductivity type is n-type, and if the first conductivity type is n-type, the second conductivity type is p-type.

According to the present invention, in order to solve the above-mentioned problems, (3) a light source for emitting a light beam is displaced so as to relatively cross the light beam, and the light beam is irradiated. It has a scale in which an optical pattern of a predetermined period is formed in a region, and a light receiving array unit that receives the light beam passing through the scale, and a light shielding unit is provided between elements of the light receiving array unit. Is provided.

(Corresponding Embodiment of the Invention) The second embodiment corresponds to the second embodiment.

According to the present invention, in order to solve the above-mentioned problems, (4) a light source unit for emitting a light beam is displaced so as to relatively cross the light beam, and the light beam is irradiated. A scale in which an optical pattern of a predetermined period is formed in a region, and a light receiving array unit that receives the light beam passing through the scale, and a light shielding unit is provided around the light receiving array unit. An optical encoder is provided.

(Corresponding Embodiment of the Invention) The third embodiment corresponds to the third embodiment.

According to the present invention, in order to solve the above problems, (5) a light source unit for emitting a light beam, a driving circuit unit for driving the light source unit, and a light source unit that crosses the light beam relatively. And a scale in which an optical pattern having a predetermined period is formed in an area irradiated with the light beam, a light receiving unit that receives the light beam passing through the scale, and a signal processing that processes an output of the light receiving unit An optical encoder having a circuit section, wherein an electrical ground of the drive circuit section and an electrical ground of the signal processing circuit section are separated.

(Corresponding Embodiment of the Invention) The fourth embodiment corresponds to the fourth embodiment.

[0049]

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

(First Embodiment) <Electrode Extraction on Substrate Side> (Configuration) In FIG. 1A, the encoder is roughly divided into a base 1, a surface emitting laser 2, a photo IC 3, and a scale 4 Consists of two parts.

In this case, the base 1, the surface emitting laser 2, and the photo IC 3 are integrally formed as a main body, and the scale 4
Is held while maintaining a proper posture with a gap d.

On a base 1, a surface emitting laser 2 for emitting a beam 2a arranged obliquely with respect to a scale 4.
And a photo I comprising a light receiving array section 3a in which a plurality of array elements having the same structure are arranged at a pitch Pp and a signal processing circuit 3b.
C3 is formed.

Instead of the surface emitting laser 2 in this example,
An ordinary semiconductor laser or the like may be used as the light source.

The wavelength of this light source is 800 nm to 1000 n.
m, and the light receiving array section 3a is a silicon-based semiconductor layer.

In the case where light sources having different wavelengths are used, it is possible to cope with the situation by using a light receiving section which is desirable for detecting the wavelength.

The signal processing circuit 3b includes a laser driving circuit,
And a normalizing circuit for adjusting the gain / offset of the signal of the light receiving array section 3a.

One of the sums of the signals of every fourth array element of the light receiving array section 3a is an A (+) signal, the sum of the signals of every fourth array element adjacent thereto is a B (+) signal, and The sum of the signals of every fourth array element adjacent to the fourth array element is an A (-) signal, and the sum of the signals of the remaining fourth array elements is a B (-) signal.

[A (+)-A (-)] is output as an A signal, and [B (+)-B (1)] is output as a B signal, and these two A signals and B signals are output as encoder signals. Thus, the signal processing circuit 3b is configured.

The scale 4 has an optical pattern 4a in which two patterns having different reflectivities are arranged at a pitch Ps of several tens of μm.

Here, the following relationship exists between the arrangement pitch Pp of the array elements in the light receiving array section 3a and the arrangement pitch Ps of the optical patterns 4a in the scale 4.

Pp = 2Ps In the optical encoder of this embodiment, the laser light beam 2a emitted from the surface emitting laser 2 is incident on the optical pattern 4a of the scale 4 with a spread.
Each part is arranged and configured such that the laser light beam 2a diffracted by a is incident on the light receiving array part 3a.

The surface emitting laser 2 and the photo IC 3 are arranged so that their heights in the z direction in FIG. 1A are equal.

The gap d is determined so that an image twice as large as the image on the optical pattern 4a of the scale 4 is formed on the light receiving array section 3a.

The range in which the resolution is increased depends on the wavelength and the emission angle of the laser beam.

In this example, a diffraction image by reflection at the lower surface of the scale 4 is used. However, the light receiving portion may be arranged above the scale 4 in the drawing by using light transmitted to the upper surface of the scale 4. It is possible.

In this case, the gap between the light source and the scale and the gap between the scale and the light receiving section are selected so as to increase the resolution depending on the wavelength and the emission angle, and the distance between these two gaps may not necessarily be equal.

However, when these two gap amounts are different, the following relationship is established between the scale pitch and the pitch of the light receiving array section.

Ps: Pp = (gap amount between light source and scale): × 4 (gap amount between light source and scale + gap amount between scale and light receiving unit) Then, gap d between base 1 and scale 4 is Constant, in the pitch direction of the scale 4, ie, FIG.
It is arranged so as to be relatively movable in the middle x direction.

Regarding the configuration described above, even in a configuration that uses a light source that collimates the light from the light emitting unit with a condenser lens or the like, which is mainly used in a conventional optical system, the imaging condition By arranging the light source, the scale, and the light receiving unit so as to satisfy the following, the operations and effects described below can be obtained.

However, the following relationship is established between the scale pitch Ps and the PD array pitch Pp in this case.

Ps: Pp = 4: 1 FIG. 1B shows the cross-sectional structure of one element of the light receiving array section 3a.

The structure of one element of the light receiving array section 3a is as follows.
The p-type semiconductor layer 301, the n-type semiconductor layer 302, the p-type semiconductor layer 303, and the p-type semiconductor layer 301, the n-type semiconductor layer 302, and the p-type semiconductor layer 30 from the upper side on the light receiving surface side.
The electrode 301a and the electrode 302 provided for
a, electrode 303a.

Here, each of the semiconductor layers of the p-type semiconductor layer 301, the n-type semiconductor layer 302, and the p-type semiconductor layer 303 is based on Si and implanted with a p-type or n-type dopant. .

Of these, the p-type semiconductor layer 303 serving as the substrate
Has a thickness of several 100 μm, and the other portions of the p-type semiconductor layer 301 and the n-type semiconductor layer 302 have a thickness of several μm to
It has a thickness of several tens of μm.

The electrode 302a is connected to an electric ground, and a negative (-) voltage is applied to the electrode 301a and the electrode 303a.

This configuration can be another configuration as described below.

(Alternative Configuration 1) N-type semiconductor layer 301, P-type semiconductor layer 302, N-type semiconductor 30
It is composed of three layers and an electrode 301a, an electrode 302a, and an electrode 303a provided in each of the n-type semiconductor layer 301, the p-type semiconductor layer 302, and the n-type semiconductor 303 layer.

Here, the electrode 302a is connected to an electrical ground, and a positive (+) voltage is applied to the electrode 301a and the electrode 303a.

(Alternative Configuration 2) From the upper side on the light receiving surface side, a metal layer 301, an n-type semiconductor layer 302, a p-type semiconductor layer 303,
And an electrode 301a and an electrode 30 provided on each of the metal layer 301, the n-type semiconductor, and the p-type semiconductor layer 303.
2a and an electrode 303a.

However, a metal layer having a rectifying action with the n-type semiconductor layer 302 is selected as the metal layer 301.

Here, the electrode 302a is connected to an electrical ground, and a negative (-) voltage is applied to the electrode 301a and the electrode 303a.

(Alternative Configuration 3) A metal layer 301, a p-type semiconductor layer 302, an n-type semiconductor layer 303,
And an electrode 301a and an electrode 30 provided on each of the metal layer 301, the p-type semiconductor, and the n-type semiconductor layer 303.
2a and an electrode 303a.

However, a metal layer having a rectifying effect with respect to the p-type semiconductor layer 302 is selected as the metal layer 301.

Here, the electrode 302a is connected to the electric ground, and a positive (+) voltage is applied to the electrode 301a and the electrode 303a.

(Operation) <Position Detection> First, a position detection function as an optical encoder will be described.

The laser light beam 2 a emitted from the surface emitting laser 2 enters the optical pattern 4 a of the scale 4.

Then, the laser light beam reflected by the optical pattern 4a is detected by the light receiving array section 3a.

When the base 1 and the scale 4 move relatively, the electric signal detected by the light receiving array section 3a changes in intensity as a triangular wave.

Since the two electric signals A and B detected by the light receiving array unit 3a have a phase difference of 1/4 cycle,
Base A including the relative movement direction using two signals A and B
And the amount of relative movement of the scale 4 can be known.

<Reduction of Crosstalk> The laser beam incident on the light receiving array section 3a is detected as follows.

In order to detect the laser beam, the electrode 302a of the light receiving array section 3a is connected to an electric ground, and a voltage of minus (-) several V is applied to the electrode 301a and the electrode 303a.

A part of the light transmitted through the p-type semiconductor layer 301 and reaching the n-type semiconductor layer 302 is absorbed and generates electrons and holes by the photoelectric effect.

In this case, the proportion of light absorbed by the n-type semiconductor layer 302 is several percent to several tens percent, depending on the wavelength.

At this time, of the electrons and holes generated in the n-type semiconductor layer 302, the electrons are attracted to the electrode 302a which is an electric ground, and the holes are the electrodes to which a voltage of minus (−) several V is applied. It is mainly drawn to 301a.

Most of the light not absorbed by the n-type semiconductor layer 302 escapes to the p-type semiconductor layer 303.

Usually, since the p-type semiconductor layer 303 serving as the substrate is as thick as several hundred μm, almost all the incident light is absorbed here to generate electrons and holes.

At this time, of the electrons and holes generated in the p-type semiconductor layer 303, the electrons are the electrodes 3 which are the electric ground.
02a.

Further, for the holes, since a voltage of minus (−) several V is applied to the p-type semiconductor layer 303,
It is mainly drawn to a.

What is detected in each element array of the light receiving array section 3a is a hole attracted to the electrode 301a.

Therefore, when a voltage of minus (-) several V is applied to the electrode 303a, the light absorbed by the p-type semiconductor layer 301 is detected from the light entering each element of the light receiving array section 3a. You can do it.

When a voltage of minus (-) several volts is not applied to the electrode 303a, holes generated in the p-type semiconductor layer 303 diffuse in the p-type semiconductor layer 303 serving as a substrate, and any of the light receiving arrays Electrode 301 in element array of part 3a
It is drawn to a.

In this case, a minus (-) is applied to the electrode 303a.
In addition to the light detection when there is an applied voltage of several V, the light reaching the p-type semiconductor layer 303 is also diffused and
This is detected by the element a, which causes crosstalk.

In this case, the pitch Pp of the light receiving array 3a
Is large enough, the effect of diffusion is small and the amount of crosstalk is negligible.

However, when the pitch Pp becomes smaller, the influence of diffusion becomes larger. In particular, light incident near the boundary between elements of the light receiving array portion 3a affects light detection by two adjacent elements.

In FIG. 5B showing the prior art, n
Although the thickness of the n-type semiconductor layer 302 is several hundred μm, in this embodiment, the thickness of the n-type semiconductor layer 302 is several μm to several tens of μm.
μm, and a P-type semiconductor layer 303 having a thickness of several hundred μm is provided thereunder.

For this reason, in the prior art shown in FIG. 5B, a large amount of light is absorbed by the n-type semiconductor layer 302. In the present embodiment, the n-type semiconductor layer 302 depends on the wavelength.
The ratio of light absorbed by is only a few% to several tens%,
Most of the light escapes to the P-type semiconductor layer 303, and almost all the light that has escaped is absorbed by the P-type semiconductor layer 303.

For this reason, in the present embodiment, crosstalk can be effectively reduced by controlling electrons and holes generated in the P-type semiconductor layer 303.

(Effect) Therefore, the vertical cross-sectional structure of the light receiving array section is made to be a pnp semiconductor layer structure, and a lead electrode is provided on the substrate side and a reverse bias of several volts is applied to the lead electrode, thereby greatly increasing crosstalk. It is possible to reduce to.

This means that the vertical cross-sectional structure of the light receiving array section is the same as the structure of the npn semiconductor layer (Alternative Configuration 1 described above), or the pnp semiconductor layer and the npn semiconductor layer The same applies to a structure in which the light receiving surface is replaced by a metal layer in the two structures (the other configurations 2 and 3 described above).

By reducing the crosstalk, it is possible to reduce the noise level and supply an encoder with higher resolution and higher position detection accuracy.

Further, the amount of crosstalk can be controlled by adjusting the amount of voltage applied to the substrate side.

Even if the encoder signal output is ideally a triangular wave, the encoder signal can be made closer to a sine wave by controlling the amount of crosstalk.

(Second Embodiment) <Shading Between Elements of Light-receiving Array Unit> (Configuration) The outline of the configuration of the second embodiment is the same as the outline of the configuration of the above-described first embodiment. This is the same as FIG.

Therefore, here, the structure of the light receiving array portion 3a which is different from the structure of the first embodiment will be described.

FIG. 2A shows a planar structure of a light receiving array section 3a according to the second embodiment.

The light receiving surface of each element array is composed of a light receiving window 31a that transmits light and a light shielding plate 31b that is arranged between adjacent light receiving windows 31a and blocks light.

FIG. 2B shows a planar structure of the light receiving array section 3a according to the first embodiment. In this case, only the light receiving windows 31a that transmit light are present and are adjacent to each other. Light shielding plate 31 interposed between light receiving windows 31a for blocking light
b does not exist.

In the second embodiment, if the light transmittance of the light shielding plate 31b is sufficiently lower than that of the light receiving window 31a, the light shielding plate 31b can perform its function without completely blocking the light.

FIG. 2C shows an example of a sectional structure of one element of the light receiving array section 3a according to the second embodiment.

The structure of one element of the light receiving array section 3a is as follows.
Similar to a photodiode, p
Semiconductor layer 301, n-type semiconductor layer 302, n-type semiconductor layer 303, p-type semiconductor layer 301, n-type semiconductor layer 30
2, electrode 301a and electrode 302a
Consists of

Note that there is no functional problem even if the n-type semiconductor layer 303 is omitted.

Each semiconductor layer is based on Si and has a p-type or n-type dopant implanted therein.

The n-type semiconductor layer 303 serving as a substrate has a thickness of several 100 μm, and the other two portions have a thickness of several μm to several tens μm.

However, when the n-type semiconductor layer 303 is omitted, the thickness of the n-type semiconductor layer 302 is several hundred μm.
m.

The electrode 302a is connected to an electrical ground, and a negative (-) voltage is applied to the electrode 301a.

It is to be noted that this configuration can be another configuration as described below.

(Alternative Configuration 1) n-type semiconductor layer 301, p-type semiconductor layer 302, n-type semiconductor layer 3
03, and an n-type semiconductor layer 301 and a p-type semiconductor layer 302
And an electrode 301a and an electrode 302a provided respectively.

The electrode 302a is connected to an electrical ground, and a positive (+) voltage is applied to the electrode 301a.

(Alternative Configuration 2) The metal layer 301, the n-type semiconductor layer 302, the p-type semiconductor layer 303,
And an electrode 301a, an electrode 302a, and an electrode 303a provided on the metal layer 301 and the n-type semiconductor layer 302, respectively.
Consists of

However, a metal layer having a rectifying action with the n-type semiconductor layer 302 is selected as the metal layer 301.

The electrode 302a is connected to an electric ground, and a negative (-) voltage is applied to the electrode 301a.

(Alternative Configuration 3) The metal layer 301, the p-type semiconductor layer 302, the n-type semiconductor layer 303,
And an electrode 301a and an electrode 3 provided on the metal layer 301, the p-type semiconductor layer 302, and the n-type semiconductor layer 303, respectively.
02a and an electrode 303a.

However, as the metal layer 301, a metal layer having a rectifying action with the p-type semiconductor layer 302 is selected.

The electrode 302a is connected to an electric ground, and a positive (+) voltage is applied to the electrode 301a and the electrode 303a.

(Operation) <Position Detection> The position detection function as the optical encoder is the same as that of the first embodiment.

<Reduction of Crosstalk> The laser beam incident on the light receiving array section 3a is detected as follows.

In order to detect the laser beam, the electrode 3
02a is connected to an electrical ground, and a voltage of minus (-) several V is applied to the electrode 301a.

Of the light incident on the light receiving surface of each element, the light impinging on the light shielding plate 31b is blocked and does not reach below, but only the light passing through the light receiving window 31a propagates to the lower part.

A part of the light that has passed through the p-type semiconductor layer 301 and reached the n-type semiconductor layer 302 is absorbed and generates electrons and holes by the photoelectric effect.

In this case, the proportion of light absorbed by the n-type semiconductor layer 302 is several percent to several tens percent, depending on the wavelength.

At this time, electrons generated in the n-type semiconductor layer 302 are attracted to the electrode 302a which is an electric ground, and holes are applied with a voltage of minus (−) several V to the p-type semiconductor layer 301. The electrode 301a
It is mainly drawn to.

Most of the light not absorbed by the n-type semiconductor layer 302 escapes to the p-type semiconductor layer 303.

Usually, since the p-type semiconductor layer 303 as the substrate is as thick as several hundreds of μm, almost all the incident light is absorbed here to generate electrons and holes.

[0144] Of the electrons and holes generated in the p-type semiconductor layer 303, the electrons are the electrodes 30 serving as the electrical ground.
The holes are attracted to 2a, and the holes are diffused in the p-type semiconductor layer 303 as a substrate, and are attracted to the electrode 301a in the element array of any of the light receiving array units 3a.

What is detected by each element of the light receiving array section 3a is a hole attracted to the electrode 301a.

In addition to the light detection in the n-type semiconductor layer 302,
The light that has reached the p-type semiconductor layer 303 is also diffused and detected by the elements of each light receiving array unit 3a, and the latter causes crosstalk.

In this case, the pitch Pp of the light receiving array portion 3a
Is large enough, the effect of diffusion is small and the amount of crosstalk is negligible.

However, as the pitch Pp becomes smaller, the influence of diffusion becomes larger. In particular, light incident near the boundary between elements of the light receiving array section 3a affects light detection by two adjacent elements.

(Effect) The degree of diffusion of holes generated in the p-type semiconductor layer 303 affects crosstalk.

Accordingly, if the width of the light shielding plate 31b can be selected so that holes do not diffuse from the generation point to the adjacent element of another light receiving array portion 3a and a sufficient amount of light can be detected, crosstalk can be reduced. And the SN ratio is improved.

This means that the structure of the pnp semiconductor layer is changed to the structure of the npn semiconductor layer as the vertical cross-sectional structure of the light receiving array section 3, or the pnp semiconductor layer, np
The same applies to a structure in which the light receiving surface is replaced with a metal in the two structures of the −n semiconductor layer.

By reducing the crosstalk, the noise level is reduced, and it is possible to supply an encoder with higher resolution and higher position detection accuracy.

Further, by adjusting the width of the light shielding plate 31b, the amount of crosstalk can be controlled.

That is, even if the encoder signal output is ideally a triangular wave, the encoder signal can be made closer to a sine wave by controlling the amount of crosstalk.

(Third Embodiment) <Offset Reduction by Providing Light-Shielding Area around Light-Receiving Array Unit> (Configuration) The outline of the configuration of the third embodiment is as described in the first embodiment. It is the same as FIG. 1A showing the outline of the configuration of the embodiment.

Therefore, here, the structure of the light receiving array section 3a which is different from the structure of the first embodiment will be described.

FIG. 3 shows a planar structure of the light receiving array section 3a according to the present embodiment.

The light receiving array 3a is made up of elements 31a having the same shape, and a light shielding area 31b for blocking light is arranged around the element 31a.

If the light transmittance of the light-shielding region 31b is sufficiently lower than that of the light-receiving array element 31a, the light-shielding region 31b can perform its function without completely blocking the light.

In the third embodiment, the planar structure of the light receiving array section 3a when the light shielding area 31b is not provided is as shown in FIG. 2B (corresponding to the first embodiment described above). The same is true.

Further, in the third embodiment, the cross-sectional structure of one element of the light receiving array section 3a is the same as that in FIG. 2C in the above-described second embodiment.

(Operation) <Position Detection> The position detecting function as the optical encoder is the same as that in the first embodiment.

<Offset Reduction> The laser light beam incident on the light receiving array section 3a is detected as follows.

In order to detect the laser beam, the electrode 3
02a is connected to an electrical ground, and applies a voltage of minus (−) several V to the electrode 301a.

Of the light incident on the photo IC 3, the light that strikes the light-shielding region 31b is cut off and does not reach below, but only the light that has passed through the light receiving array 3a is propagated below.

Then, the light is transmitted through the p-type semiconductor layer 301 and n
Part of the light that reaches the type semiconductor layer 302 is absorbed and generates electrons and holes by the photoelectric effect.

Here, the ratio of the light absorbed by the n-type semiconductor layer 302 is several% to several tens% depending on the wavelength.

At this time, electrons generated in the n-type semiconductor layer 302 are attracted to the electrode 302a which is an electric ground.

The holes generated in the n-type semiconductor layer 302 are mainly attracted to the electrode 301a to which a voltage of minus (-) several V is applied.

Most of the light not absorbed by the n-type semiconductor 302 escapes to the p-type semiconductor layer 303.

Normally, since the p-type semiconductor layer 303 serving as the substrate is as thick as several hundreds of μm, almost all incident light is absorbed here, and electrons and holes (holes) are generated by the photoelectric effect.
Generate.

Then, electrons generated in the p-type semiconductor layer 303 are attracted to the electrode 302a which is an electric ground.

The holes generated in the p-type semiconductor layer 303 diffuse in the p-type semiconductor layer 303 serving as a substrate, and are drawn to the electrode 301a in one of the elements of the light receiving array section 3a.

Thus, what is detected by each element of the light receiving array section 3a is a hole attracted to the electrode 301a.

In this case, in addition to the light detection in the n-type semiconductor layer 302, the light reaching the p-type semiconductor layer 303 is also diffused and detected by the elements of each light receiving array section 3a.

The latter causes crosstalk.

When the pitch Pp of the light receiving array section 3a is sufficiently large, the influence of diffusion is small and the amount of crosstalk can be ignored.

However, as the pitch Pp becomes smaller, the influence of diffusion becomes greater. In particular, light incident near the boundary of the main line of the light receiving array section 3a affects light detection by two adjacent elements.

When there is no light-shielding region 31b, part of the light emitted around the light receiving array portion 3a propagates to the lower layer portion.

The holes generated in the n-type semiconductor layer 302 and the holes generated by light absorption in the lower layer are diffused, and a part of the holes is propagated from the outer periphery of the light receiving array portion 3a to the inside to be detected. .

This is the offset in the light detection.

At this time, since the array elements at both ends of the light receiving array portion 3a have a large boundary portion with the outer peripheral portion, they are particularly susceptible to the diffusion of holes, and a large offset is likely to occur in light detection.

In calculating the encoder signals A and B,
[A (+)-A (-)] is A signal, [B (+)-B
(-)] Is a B signal, so that even if all array elements are evenly offset, they are canceled.

However, when there is no light-shielding region 31b, particularly large offsets are likely to be applied to the array elements at both ends, and this affects the offsets of the encoder signals A and B.

In the configuration shown in FIG. 3, a similar function can be realized by providing a light receiving portion instead of the light-shielding region 31b and extracting holes generated.

Further, by providing a light receiving portion on the outer peripheral portion of the light receiving portion region for encoder signal detection and further providing a light shielding region thereon, it is possible to reduce unnecessary offset due to diffusion of holes.

(Effect) The diffusion of holes generated around the light receiving array portion 3a affects the offset.

Therefore, the offset of the encoder signal can be reduced by providing the light shielding region 31b so as not to generate holes.

This effect is obtained by providing a pseudo light receiving section instead of the light shielding area on the outer periphery of the light receiving array section 3a for detecting the encoder signal, inducing holes generated inside and diffusing the holes. A similar effect can be expected by suppressing.

The same applies to an encoder that performs light detection by the photoelectric effect regardless of the vertical sectional structure of the light receiving array section.

It is to be noted that, even in an encoder in which the light receiving section is not in the form of an array, the offset on the encoder signal can be reduced by the light shielding area around the light receiving section regardless of the use of the scale diffraction image.

In an encoder having an encoder signal offset / cancel function, fine adjustment of the offset amount is not required, and the entire circuit can be simplified.

By reducing the offset of the encoder signal, it is possible to provide an encoder with higher resolution and higher position detection accuracy.

By combining the above-described second embodiment and the third embodiment, a light-shielding portion is provided between elements of the light-receiving array portion, and a light-shielding region is provided around the light-receiving array portion. With this configuration, crosstalk and offset can be reduced at the same time.

(Fourth Embodiment) <Offset Reduction by Dividing Electrical Ground Around Semiconductor Laser and Light Receiving Element> (Structure) The outline of the structure of the fourth embodiment is as described in the first embodiment. This is the same as FIG. 1A showing the outline of the configuration of the embodiment.

Therefore, here, the structure of the base 1 which is different from the structure of the above-described first embodiment will be described.

FIG. 4 shows a plan structure of the base 1 according to the fourth embodiment.

In FIG. 4, a surface emitting laser 2 and a photo IC 3 comprising a light receiving array section 3a and a signal processing circuit 3b are formed on a base 1.

The signal processing circuit 3b includes a laser driving circuit,
And a normalizing circuit for adjusting the gain / offset of the signal of the light receiving array section 3a.

The photo IC 3 has at least six input / output terminals.

These input / output terminals are a power supply (Vdd) terminal 3c, an encoder signal ground (GND) terminal 3c.
d, a surface emitting laser ground (GND) terminal 3e, a surface emitting laser drive level setting voltage terminal 3f, an encoder signal A terminal 3g, and an encoder signal B terminal 3h.

In this case, the ground (GND) terminal 3d for the encoder signal and the ground (G
It is characterized in that the ND) terminal 3e is provided separately.

Further, between the surface emitting laser 2 and the photo IC 3, two wirings L1 and L2 for supplying a driving current for the surface emitting laser 2 are provided.
L2 is connected.

(Operation) <Position Detection> The position detection function as an encoder is the same as that of the first embodiment.

<Offset Reduction> An encoder signal is obtained by subjecting a signal obtained by the light receiving array unit 3a to current-voltage conversion by a normalization circuit of the signal processing circuit 3b and performing gain adjustment and the like.

In the gain adjustment for obtaining the encoder signal, a high gain is given based on the voltage of the electric ground line.

Therefore, a small offset on the electrical ground line causes a large offset on the encoder signal.

Since the power supply line also has wiring resistance, if a large current flows, a potential displacement occurs from the electrical ground at the wiring end, which affects the offset of the encoder signal.

In an encoder signal processing section such as the light receiving array section 3a and the signal processing circuit 3b, a current of about 1 mA flows for a supply voltage of about 5V.

On the other hand, regarding the laser drive circuit,
In a semiconductor laser for a sensor, a current of several tens mA flows when a voltage of usually about 2 to 3 V is applied.

Therefore, a current that is approximately one digit larger flows through the laser drive circuit.

In this embodiment, the ground (GND) terminal 3d for encoder signal and the ground (GND) terminal 3e for surface emitting laser are separately provided, so that the electrical ground line of the laser drive unit and the encoder signal processing are provided. Since the electric ground line is separated from the electric ground line, the influence of the offset of the electric ground line due to the laser drive circuit having a large current is not transmitted to the encoder signal processing unit.

Therefore, the influence of the offset of the electric ground is reduced to a value that is about one digit smaller.

(Effect) The offset of the electrical ground line of the encoder signal processing section such as the light receiving array section 3a and the signal processing circuit 3b affects the offset of the encoder signal.

By providing the electrical ground line on the laser drive circuit side having a large amount of current separately from the electrical ground line of the encoder signal processing unit, the influence of the electrical ground offset is reduced by about one digit. Can be reduced.

The same applies to an encoder that performs light detection by the photoelectric effect regardless of the vertical sectional structure of the light receiving array section.

It should be noted that, even in an encoder of which the light receiving section is not in the form of an array, the offset on the encoder signal can be reduced by dividing the electrical ground regardless of the use of the scale diffraction image.

Further, in an encoder having an encoder signal offset / cancel function, fine adjustment of the offset amount is not required, and the entire circuit can be simplified.

By reducing the offset of the encoder signal, an encoder with higher resolution and higher position detection accuracy can be supplied.

[0220] In the present specification described in the above embodiments, in addition to claims 1 to 3 set forth in the appended claims, the inventions described below as appendices 1 to 9 are described. include.

(Supplementary Note 1) A light source unit for emitting a light beam, a scale displaced so as to relatively cross the light beam, and an optical pattern having a predetermined period formed in a region irradiated with the light beam; An optical encoder having an array-shaped light-receiving portion formed of an array for detecting a predetermined portion of the diffraction pattern of the optical pattern on the scale, which is generated by the light beam, wherein the array-shaped light-receiving portion is located on the substrate side. The first conductivity type, the second
An optical encoder comprising three semiconductor layers of a conductivity type and a first conductivity type, wherein an electrode capable of applying a reverse bias voltage is provided on the semiconductor layer of the first conductivity type on the substrate side.

(Corresponding Embodiment of the Invention) The first embodiment corresponds to this.

(Supplementary Note 2) A light source unit for emitting a light beam, a scale displaced so as to relatively cross the light beam, and an optical pattern having a predetermined period formed in a region irradiated with the light beam; An optical encoder having an array-shaped light-receiving portion formed of an array for detecting a predetermined portion of the diffraction pattern of the optical pattern on the scale, which is generated by the light beam, wherein the array-shaped light-receiving portion is located on the substrate side. The first conductivity type, the second
An electrode configured to include a semiconductor layer of a conductivity type and a metal layer having a rectifying effect on the semiconductor layer of the second conductivity type; and an electrode capable of applying a reverse bias to the semiconductor layer of the first conductivity type. An optical encoder characterized in that:

(Corresponding Embodiment of the Invention) The first embodiment corresponds to this.

(Supplementary Note 3) A light source unit that emits a light beam, a light source unit that emits a light beam, and a light source unit that is displaced so as to intersect the light beam relatively, and that a predetermined period of time A scale on which an optical pattern is formed,
An optical receiver comprising an array for detecting a predetermined portion of the diffraction pattern of the optical pattern on the scale, which is generated by the light beam, wherein the light is shielded between the arrays of the array of light receivers. An optical encoder having an area.

(Corresponding Embodiment of the Invention) The second embodiment corresponds to the second embodiment.

(Supplementary Note 4) A light source unit for emitting a light beam, a scale displaced so as to relatively cross the light beam, and an optical pattern having a predetermined period formed in a region irradiated with the light beam, An optical encoder comprising: a light receiving unit for detecting light reflected or transmitted by the optical pattern on the optical pattern, wherein a light shielding area is provided around the light receiving unit.

(Corresponding Embodiment of the Invention) The third embodiment corresponds to the third embodiment.

(Supplementary Note 5) The optical encoder according to Supplementary Note 5, wherein the light receiving unit is constituted by a light receiving array for detecting a predetermined portion of a diffraction pattern of the optical pattern on the scale.

(Corresponding Embodiment of the Invention) The third embodiment corresponds to the third embodiment.

(Supplementary Note 6) A light source unit for emitting a light beam, a scale displaced so as to relatively cross the light beam, and an optical pattern having a predetermined period formed in a region irradiated with the light beam; An optical encoder having a light receiving portion for detecting light transmitted or reflected by the optical pattern, wherein a light receiving region is provided on an outer peripheral portion of the light receiving portion; Encoder. (Corresponding Embodiment of the Invention) The third embodiment corresponds to the third embodiment.

(Supplementary Note 7) The supplementary note 7, wherein the light receiving portion is constituted by a light receiving array for detecting a predetermined portion of a diffraction pattern of the optical pattern on the scale.
An optical encoder as described.

(Corresponding Embodiment of the Invention) The third embodiment corresponds to the third embodiment.

(Supplementary Note 8) A light source unit for emitting a light beam, a scale displaced so as to relatively cross the light beam, and an optical pattern having a predetermined period formed in a region irradiated with the light beam, A light receiving unit for detecting light transmitted or reflected by the optical pattern, or a signal processing circuit for processing a signal obtained from the light receiving unit; Drive circuit, the light receiving section, the signal processing circuit section, or a part of each of these circuits, hybrid, or monolithically formed integrally, and the light receiving section, and the signal processing circuit section Electrical ground of the drive circuit of the light source unit is separated from the electrical ground,
An optical encoder, which is provided separately.

(Corresponding Embodiment of the Invention) The fourth embodiment corresponds to the fourth embodiment.

(Supplementary note 9) The supplementary note 9, wherein the light receiving section is constituted by a light receiving array for detecting a predetermined portion of a diffraction pattern of the optical pattern on the scale.
An optical encoder as described.

(Corresponding Embodiment of the Invention) The fourth embodiment corresponds to the fourth embodiment.

[0238]

Therefore, as described above, according to the present invention, it is possible to provide an optical encoder having a configuration in which an offset or a waveform distortion is hardly generated in an encoder signal, and which is capable of maximizing performance. it can.

[Brief description of the drawings]

FIG. 1A is a diagram showing an outline of a configuration of a first embodiment of an optical encoder according to the present invention, and FIG.
2B is a diagram illustrating a cross-sectional structure of one element of the light receiving array unit 3a in FIG.

FIG. 2A is a diagram illustrating a planar structure of a light receiving array unit 3a according to a second embodiment of the optical encoder according to the present invention, and FIG. 2B is a diagram illustrating the first embodiment; It is a figure which shows the planar structure of the light receiving array part 3a by embodiment, FIG.2 (c) is a figure which shows the cross-sectional example of one element of the light receiving array part 3a in 2nd Embodiment.

FIG. 3 shows a third embodiment of the optical encoder according to the invention;
FIG. 5 is a diagram showing a planar structure of a light receiving array unit 3a according to the embodiment.

FIG. 4 shows a fourth embodiment of the optical encoder according to the invention;
FIG. 3 is a diagram showing a planar structure of a base 1 according to the embodiment.

5A is a diagram showing a basic configuration of a microencoder according to a conventional technique, and FIG. 5B is a diagram showing a cross-sectional structure of a PD which is a general light receiving element. ,
FIG. 5C is a diagram showing a conventional technique of an array-shaped light receiving unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Base, 2 ... Surface emitting laser, 3 ... Photo IC, 4 ... Scale, 2a ... Laser beam, 3a ... Light receiving array part, 3b ... Signal processing circuit, 4a ... Optical pattern, 301 ... P-type semiconductor layer, 302 ... n-type semiconductor layer, 303 ... p-type semiconductor layer, 301a ... electrode, 302a ... electrode, 303a ... electrode, 31a ... light receiving window (light receiving array element), 31b ... light shielding plate (light shielding area), 3c ... power supply (Vdd) Terminal, 3d: ground (GND) terminal for encoder signal, 3e: ground (GND) terminal for surface-emitting laser, 3f: surface-emitting laser drive level setting voltage terminal, 3g: encoder signal A terminal, 3h: encoder signal B terminal, L1, L2: wirings for supplying the driving current of the surface emitting laser 2.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Eiji Yamamoto Inventor F-term (reference) 2F065 AA02 AA07 AA09 BB02 BB13 BB15 BB29 FF16 FF18 FF48 GG04 GG15 2-43-2 Hatagaya, Shibuya-ku, Tokyo HH05 HH12 JJ00 JJ05 JJ24 LL28 MM03 QQ28 2F103 BA00 BA08 BA31 CA03 CA04 DA01 DA12 EA02 EA05 EA15 EB02 EB07 EB12 EB15 EB32 EB37 FA12 4M118 AA05 AB02 BA06 CA03 CA06 5F049 NA03 NB07 RA02 RA08

Claims (5)

[Claims] A light source unit for emitting a light beam; a scale displaced to relatively cross the light beam; and an optical pattern having a predetermined period formed in an area irradiated with the light beam; A light-receiving array section that receives the light beam passing through the first semiconductor layer, a first conductive-type semiconductor layer, a second conductive-type semiconductor layer, An optical encoder, wherein a reverse bias voltage is applied to a conductive semiconductor layer and a first conductive semiconductor layer on the substrate side. 2. A light source unit for emitting a light beam, a scale displaced so as to relatively cross the light beam, and an optical pattern having a predetermined period formed in a region irradiated with the light beam; A light-receiving array unit that receives the light beam passing through the light-receiving device, wherein the light-receiving array unit includes a first conductive type semiconductor layer, a second conductive type semiconductor layer, A metal layer having a rectifying effect on the two-conductivity type semiconductor layer,
An optical encoder, wherein a reverse bias voltage is applied to the first conductivity type semiconductor layer on the substrate side. 3. A light source unit for emitting a light beam, a scale displaced so as to relatively cross the light beam, and an optical pattern having a predetermined period formed in a region irradiated with the light beam; An optical encoder comprising: a light receiving array unit that receives the light beam passing through the light receiving unit; and a light blocking unit provided between elements of the light receiving array unit. 4. A light source unit for emitting a light beam, a scale displaced to relatively cross the light beam, and an optical pattern having a predetermined period formed in a region irradiated with the light beam; An optical encoder comprising: a light receiving array unit that receives the light beam passing through the light receiving unit; and a light blocking unit provided around the light receiving array unit. 5. A light source unit for emitting a light beam; a driving circuit unit for driving the light source unit; A scale on which an optical pattern is formed, a light receiving unit for receiving the light beam passing through the scale, and a signal processing circuit unit for processing an output of the light receiving unit; An optical encoder, wherein an electrical ground of a signal processing circuit is separated.