JPH11211565A - Photosensor with signal processing function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photosensor with signal processing function in which processing at a post-stage signal processing circuit is simplified while widening the dynamic range, and conventional parts can be employed as they are. SOLUTION: The photosensor 10 delivers a signal exhibiting linear output characteristics when the illuminance of incident light is lower than a first specified level and delivers a signal exhibiting logarithmic output characteristics when the illuminance of incident light is higher than the first specified level. A characteristics converting means 12 converts the output signal from the photosensor 10 into a signal exhibiting logarithmic output characteristics corresponding to the illuminance of incident light and delivers the converted signal as a sensor signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical sensor having a signal processing function having a function of processing a signal obtained from an optical sensor (image sensor). To technology to convert to.

[0002]

2. Description of the Related Art Conventionally, a technique for measuring various physical quantities using an optical sensor is known. For example, in the field of autonomous driving of automobiles, external sensing is performed to grasp various external situations. As one of the external sensing, there is a white line detection on a road by an image sensor. The image sensor used for this white line detection can obtain an image of a white line regardless of day and night, can obtain an image of a white line included in a bright scene outside the tunnel from a dark situation inside the tunnel, and can obtain an image of a white line outside the tunnel. Severe shooting conditions are required, such as being able to obtain an image of a white line included in a dark scene in a tunnel from a bright situation. In order to satisfy such requirements, a large dynamic range is required for an image sensor used for external sensing.

In order to expand the dynamic range, the applicant of the present application disclosed an "optical sensor circuit" in Japanese Patent Application No. 8-239503 described above. Such a conventional image sensor is configured by, for example, optical sensors (pixels) arranged one-dimensionally or two-dimensionally. FIG. 10 shows a general circuit configuration of an optical sensor. This optical sensor has a gate to a photodiode PD, an n-channel MOS transistor Q1 connected in series to the photodiode PD, and a connection point (hereinafter referred to as a “sensor detection terminal”) P between the photodiode PD and the n-channel MOS transistor Q1. Are connected, and an n-channel MOS transistor Q3 connected in series with the n-channel MOS transistor Q2.

A capacitor C is connected to a sensor detection terminal P.
Is connected. The capacitor C is composed of an equivalent capacitor obtained by combining stray capacitances generated by the photodiode PD, the n-channel MOS transistor Q1, the n-channel MOS transistor Q2, and a wiring interconnecting them, and a capacitor formed in a semiconductor manufacturing process. It is formed by being done.

[0005] The photodiode PD flow sensor current I _D corresponding to the illuminance of the optical signal L _S. The n-channel MOS transistor Q1 acts as a load on the photodiode PD, and outputs a sensor current _ID flowing through the photodiode PD.
It converts the voltage to generate a detection voltage V _D to the sensor detection terminal P.

[0006] n-channel MOS transistor Q2 acts as the output transistor, in order to take out to the outside of the optical sensor detection voltage V _D as a sensor current signal, voltage - performing current conversion. The n-channel MOS transistor Q3 is
A switch circuit for supplying or stopping supply of the sensor current signal converted by the n-channel MOS transistor Q2 to an external circuit (not shown) is formed.

[0007]

FIG. 11 shows the output characteristics of the optical sensor configured as described above. This optical sensor exhibits linear output characteristics at low illuminance, that is, in a region where the sensor current _ID is small, and exhibits logarithmic output characteristics at high illuminance, that is, a region where the sensor current _ID is large. Therefore, a signal processing circuit (not shown) at the subsequent stage connected to the optical sensor cannot process the signal from the optical sensor by a simple calculation.

On the other hand, when the above-described white line detection is performed, it is known that a constant ratio always exists between the brightness of the road surface and the brightness of the white line regardless of day or night, in other words, at all brightness levels. ing. However, even if an attempt is made to perform processing on the assumption that a constant ratio always exists at all brightness levels in the signal processing circuit at the subsequent stage, the above-described conventional optical sensor has a logarithmic region with an area exhibiting indirect output characteristics. Since the same processing cannot be performed in all the areas because the areas exhibiting high output characteristics are mixed, the signal processing becomes troublesome.

As described above, a large dynamic range is required for an image sensor used for external sensing, but an optical sensor that exhibits linear output characteristics over the entire area can be obtained from the optical sensor. The range in which the magnitude of the signal can be expressed is limited. Therefore, this type of image sensor is not suitable for external sensing because the dynamic range cannot be increased. Note that a signal processing circuit that simply logarithmically compresses a signal from an optical sensor that exhibits linear output characteristics in the entire region and outputs the signal is known.

Further, as a component used in a signal processing circuit connected to the image sensor, particularly a component for image processing, a component of 8-bit specification is currently mainstream. For this reason,
It is desired that these 8-bit parts can be used as they are.

When a complicated calculation is required as in fuzzy control or when a solution cannot be easily obtained by the calculation, it is not possible to convert the output of the optical sensor using a look-up table. Are known.
For example, Japanese Patent Laying-Open No. 7-120256 discloses an example in which luminance data from an optical sensor is converted using a lookup table.

Therefore, the present invention can simplify the processing performed in the subsequent signal processing circuit, can widen the dynamic range, and can use the components used in the conventional signal processing circuit as they are. It is an object to provide an optical sensor with a signal processing function that can be used.

[0013]

In order to achieve the above object, an optical sensor with a signal processing function according to the present invention provides a signal having a linear output characteristic when the illuminance of incident light is equal to or less than a first predetermined value. An optical sensor that outputs a signal indicating a logarithmic output characteristic when the illuminance is greater than the first predetermined value;
A characteristic conversion unit that converts a signal output from the optical sensor into a signal indicating a logarithmic output characteristic according to the illuminance of incident light and outputs the signal as a sensor signal.

More specifically, the optical sensor with a signal processing function of the present invention further comprises A / D conversion means for converting an analog signal from the optical sensor into a digital signal, and wherein the characteristic conversion means comprises an A / D converter. A digital signal output from the D conversion means may be converted into a signal having logarithmic output characteristics according to the illuminance of incident light and output as a sensor signal. In this case, the characteristic conversion means can be constituted by a look-up table.

According to this optical sensor with a signal processing function,
A sensor signal showing logarithmic output characteristics is obtained in the entire range of the illuminance of the incident light. Therefore, for example, when processing is performed on the assumption that there is always a fixed ratio between the luminance of the road surface and the luminance of the white line, the same processing can be performed in the subsequent signal processing circuit, so that the signal processing is simplified. Become. Further, a sensor signal having logarithmic output characteristics can be obtained from the optical sensor with the signal processing function, so that the dynamic range can be widened.

Further, in the optical sensor with a signal processing function according to the present invention, the characteristic converting means may be configured such that the illuminance of the incident light is equal to the second
The range of the signal output when the value is equal to or less than the predetermined value and the range of the signal output when the value is larger than the second predetermined value may be converted so as to overlap and output as a sensor signal. In this case, it is determined whether the sensor signal output from the characteristic conversion means is a signal when the illuminance of the incident light is equal to or less than the second predetermined value or a signal when the illuminance is larger than the second predetermined value. And an identification signal output means for outputting an identification signal for performing the identification.

According to this configuration, for example, even when an optical sensor that outputs a 9-bit signal is used, the signal when the illuminance of the incident light is equal to or less than the second predetermined value and the second predetermined value. Since the signal is output in the overlapping range, for example, the same range as the signal in the case where the signal is larger, the sensor signal output from the optical sensor having the signal processing function is set to 8
Can be expressed in bits. Then, it is notified to the subsequent signal processing circuit using the identification signal whether the sensor signal when the current value is equal to or less than the second predetermined value or the sensor signal when the current value is larger than the second predetermined value is output. . Therefore,
The signal processing circuit can know the absolute value of the sensor signal from the optical sensor by referring to the identification signal, so that the currently mainstream 8-bit part can be used as it is.

The second predetermined value of the illuminance of the incident light is:
It can be determined independently of the first predetermined value. It is preferable that the second predetermined value is a value substantially intermediate between the maximum value and the minimum value of the output signal of the optical sensor.

Further, in the optical sensor with a signal processing function according to the present invention, the characteristic converting means may be configured so that the illuminance of the incident light is the first
First conversion means for converting a signal output from the optical sensor when the illuminance is within a range of; and a signal output from the optical sensor when the illuminance of the incident light is within a second range And second conversion means for converting
The conversion means and the second conversion means can be configured to convert and output such that the ranges of the signals output from the respective conversion means overlap. In this case, the apparatus further includes an identification signal output unit that outputs an identification signal for identifying whether the signal is a signal output from the first conversion unit or a signal output from the second conversion unit. Can be configured.

According to this configuration, the first range and the second range
By setting the range as a continuous area, the same function as the above-described optical sensor with a signal processing function can be exhibited. Further, by making the first range and the second range an overbuffered region, an illuminance signal corresponding to the overlapped region can be obtained from either of the first and second conversion means. it can.

Further, this optical sensor with a signal processing function
The signal processing apparatus may further include a signal selection unit that selects one of a signal output from the first conversion unit and a signal output from the second conversion unit. According to this configuration, it is possible to switch between the first range and the second range in response to a request from a subsequent signal processing circuit that uses a signal from the optical sensor. is there.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical sensor with a signal processing function according to an embodiment of the present invention will be described with reference to the drawings. In the following, for simplicity of description, a case will be described in which a signal from one optical sensor constituting an image sensor is processed. Note that, when simply referred to as “optical sensor” in this specification, the optical sensor is configured by a photodiode and a peripheral circuit for extracting a signal from the photodiode, for example, as shown in FIG. .

(Embodiment 1) FIG. 1 is a block diagram showing a basic configuration of an optical sensor with a signal processing function according to Embodiment 1 of the present invention. This optical sensor with a signal processing function includes an optical sensor 10, an A / D converter 11, and a look-up table 12. Look-up table 12 corresponds to the characteristic conversion means of the present invention.

As the optical sensor 10, an optical sensor disclosed by the present applicant described in the section of the prior art (see FIG. 10)
Is used. The output characteristic of the optical sensor 10 is shown in FIG.
As shown in FIGS. 3 (A), 5 (A) and 7 (A), when the illuminance of incident light is small, that is, when the sensor current is small, it is linear, and when the illuminance is large. That is, when the sensor current is large, it is logarithmic. The point at which the output characteristic changes from a linear output characteristic to a logarithmic output characteristic is hereinafter referred to as an “inflection point”. The illuminance of the incident light on the sensor surface at the inflection point corresponds to the first predetermined value of the present invention. FIG.
Shows an example where the sensor current has an inflection point near 10 ⁻¹² (A). The analog signal output from the optical sensor 10 is supplied to an A / D converter 11.

The A / D converter 11 converts an analog signal from the optical sensor 10 into a digital signal. The digital signal output from the A / D converter 11 is supplied to a look-up table 12.

The look-up table 12 comprises, for example, a memory 13 as shown in FIG. A /
The digital signal output from the D converter 11 is used as an address signal for the memory 13. When this address signal is supplied to the memory 13, data is read from the storage position of the memory 13 specified by the address signal. This read data is
This is a sensor signal output from the optical sensor having the signal processing function.

According to this configuration, a signal output from the optical sensor 10 can be converted into a sensor signal having an arbitrary output characteristic by appropriately determining data to be stored in the memory 13. In the first embodiment, the look-up table 12 includes output characteristics including a partially linear region as shown in FIG. 3A, and logarithmic logarithms over the entire region as shown in FIG. Data for conversion so as to indicate output characteristics is stored.

Therefore, when an analog signal from the optical sensor 10 having an output characteristic as shown in FIG. 3A is converted into a digital signal by the A / D converter 11 and supplied to the look-up table 12, The converted output from the look-up table 12 shows logarithmic output characteristics in all areas. Thus, even if the optical sensor partially has a region exhibiting a linear output characteristic, the entire region can be used as an optical sensor exhibiting a logarithmic output characteristic.

In the optical sensor with the signal processing function, the output characteristic of the optical sensor 10 is converted so as to have a logarithmic output characteristic in a region before the inflection point where the output characteristic is linear (a region where the illuminance of incident light is small). However, since the S / N ratio is the S / N ratio of a region having a linear output characteristic, the S / N ratio is improved as compared with an optical sensor having a logarithmic output characteristic in a region where the illuminance of incident light is small.

(Embodiment 2) FIG. 4 is a block diagram showing a configuration of an optical sensor with a signal processing function according to Embodiment 2 of the present invention. This optical sensor with a signal processing function includes an optical sensor 10, an A / D converter 11, and a look-up table 20. Look-up table 20
Corresponds to the characteristic conversion means and the identification signal output means of the present invention. The optical sensor with a signal processing function according to the second embodiment is the same as that according to the first embodiment except for the configuration of the look-up table 20.

In the optical sensor with a signal processing function according to the second embodiment, the look-up table 20
The following data is stored. That is, the output characteristic including a linear region in part as shown in FIG.
(B) logarithmic output characteristics in each of a first area where the illuminance of the incident light on the sensor surface is equal to or less than a second predetermined value a and a second area where the illuminance is larger than the second predetermined value a. And data for converting the sensor signals output from the optical sensor with the signal processing function into the same range in each area is stored.

The look-up table 20 stores identification data used as an identification signal. As the identification data, for example, data for outputting “0” when the illuminance of the incident light on the sensor surface is equal to or less than the second predetermined value, and outputting “1” when the illuminance is larger than the second predetermined value.

It should be noted that the second predetermined value is stored in the lookup table 12 (FIG. 3B) in the first embodiment.
Illuminance on the sensor surface corresponding to or near the midpoint of the converted output from the sensor output (see FIG. 1).

In this optical sensor with output processing function, FIG.
An analog signal from the optical sensor 10 having the output characteristic shown in FIG. 1A is converted into a digital signal by the A / D converter 11 and supplied to the look-up table 20. As a result, the lookup table 20 stores the digital signal from the A / D converter 11 as shown in FIG.
When the illuminance of the incident light on the sensor surface is equal to or smaller than a second predetermined value a, a sensor signal indicating a logarithmic output characteristic indicated by an output A is output.
And outputs a sensor signal indicating logarithmic output characteristics. In this case, the sensor signal indicated by the output A and the sensor signal indicated by the output B are signals in the same range.

This look-up table 20
The digital signal from the A / D converter 11 outputs an identification signal representing “0” when the illuminance of the incident light on the sensor surface is equal to or smaller than the second predetermined value a, and when the digital signal is larger than the second predetermined value a. An identification signal representing "1" is output.

As described above, the sensor signal when the illuminance of the incident light on the sensor surface is equal to or smaller than the second predetermined value a and the sensor signal when the illuminance is larger than the second predetermined value a are output in the same range. Thus, for example, the output from the optical sensor represented by 9 bits can be represented by 8 bits. As a result, it is not necessary to increase the bus width for supplying the sensor signal to the signal processing circuit in the subsequent stage, so that the signal processing circuit can use a conventionally used component of, for example, 8-bit specification as it is.

Further, since the signal processing circuit at the subsequent stage can receive the identification signal together with the sensor signal from the optical sensor having the signal processing function, it is determined that the identification signal is a signal in the first area (output A). If it indicates, the sensor signal is used as it is, and if it indicates that it is a signal in the second area (output B), a predetermined operation is performed on the sensor signal to use the signal. Can be handled in the same manner as a conventional optical sensor that can output only an 8-bit signal.

(Embodiment 3) FIG. 6 is a block diagram showing a configuration of an optical sensor with a signal processing function according to Embodiment 3 of the present invention. The optical sensor with a signal processing function includes an optical sensor 10, an A / D converter 11, a first look-up table 30, and a second look-up table 31. The first lookup table 30 corresponds to the first conversion means of the present invention, and the second lookup table 31
Corresponds to the second conversion means of the present invention. The optical sensor with a signal processing function according to the third embodiment is the same as that according to the first embodiment except that the lookup table includes two lookup tables 30 and 31.

In the optical sensor with a signal processing function according to the third embodiment, the look-up table 30 has
The output characteristic including a partially linear region as shown in FIG. 7A is changed to the first range (a1 to a2) in which the illuminance of incident light on the sensor surface as shown in the output C in FIG. , Data for conversion to show logarithmic output characteristics is stored.

Similarly, look-up table 31 contains
The output characteristic including a partly linear region as shown in FIG. 7A is changed so that the illuminance of the incident light falls within the second range (b1 to b2) as shown in the output D of FIG. 7B. In some cases, data for conversion to show logarithmic output characteristics is stored. Each data in the first and second ranges is
As in the case of the second embodiment, the sensor signals output from the optical sensors with a signal processing function are determined to have the same range. Incidentally, when the first range and the second range are continuous (when a2 and b1 have the same value), the same conversion as shown in FIG. 5B in the second embodiment is performed. Will be done.

In this optical sensor with output processing function, FIG.
An analog signal from the optical sensor 10 having the output characteristic shown in FIG. 1A is converted into a digital signal by the A / D converter 11 and supplied to the look-up table 30 and the look-up table 31. Thus, the look-up table 30 stores the A / D converter 1 as shown in FIG.
If the digital signal from 1 is a signal in the first range, it outputs a first sensor signal indicating a logarithmic output characteristic indicated by output C, and if it is a signal in the second range, it outputs B. A second sensor signal indicating the indicated logarithmic output characteristic is output.

According to the optical sensor having the output processing function,
For example, a signal from the optical sensor 10 represented by 9 bits is converted into a first sensor signal when the illuminance of the incident light on the sensor surface is in the first range and a second sensor signal when the illuminance is in the second range. Since the configuration is such that the outputs are divided and output in the same range, the first and second sensor signals can be represented by 8 bits. As a result, in the subsequent signal processing circuit, for example, a conventionally used component of 8-bit specification can be used as it is.

(Embodiment 4) FIG. 8 is a block diagram showing a configuration of an optical sensor with a signal processing function according to Embodiment 4 of the present invention. This optical sensor with a signal processing function is configured to output two sensor signals, such as the first sensor signal and the second sensor signal in the third embodiment, into one sensor signal.

This optical sensor with a signal processing function comprises an optical sensor 10, an A / D converter 11, a first look-up table 30, a second look-up table 31, and a signal selection circuit 40. The signal selection circuit 40 corresponds to the identification signal output means and the signal selection means of the present invention. The optical sensor with a signal processing function according to the fourth embodiment is configured by adding a signal selection circuit 40 to the configuration of the third embodiment. Further, the first look-up table 30 and the second look-up table 31 have data corresponding to the case where the first range and the second range are continuous, in other words, the same as shown in FIG. Is stored.

Further, the first lookup table 30 stores identification data used as an identification signal. As the identification data, for example, data for outputting “0” when the illuminance of the incident light on the sensor surface is within the first range and “1” when the illuminance is within the second range is used. In the fourth embodiment, the identification data is configured to be stored in the first lookup table 30, but may be configured to be stored in the second lookup table 31.

The signal selection circuit 40 responds to identification data (not shown) from the first lookup table 30 according to
Either the output of the first lookup table 30 or the output of the second lookup table 31 is selected and output as a sensor signal. Further, the signal selection circuit 40 generates and outputs an identification signal indicating which lookup table output is currently selected based on the identification data.

According to the optical sensor with a signal processing function of the fourth embodiment, the same effect as that of the optical sensor with a signal processing function according to the second embodiment can be obtained.

(Embodiment 5) FIG. 9 is a block diagram showing a configuration of an optical sensor with a signal processing function according to Embodiment 5 of the present invention. In the optical sensor with a signal processing function, the selection of the output from the look-up table in the signal selection circuit of the fourth embodiment is performed according to an external signal switching signal.

This optical sensor with a signal processing function comprises an optical sensor 10, an A / D converter 11, a first look-up table 30, a second look-up table 31, and a signal selection circuit 50. The signal selection circuit 50 corresponds to the identification signal output means and the signal selection means of the present invention. The first look-up table 30 and the second look-up table 31 of the optical sensor with a signal processing function according to the fifth embodiment have data corresponding to the case where the first range and the second range overlap. In other words, FIG. 7 (B)
The data for performing the conversion shown in FIG.

The signal selection circuit 50 selects either the output of the first look-up table 30 or the output of the second look-up table 31 in response to an external output switching signal and outputs it as a sensor signal. Further, the signal selection circuit 50 generates and outputs an identification signal indicating which lookup table is currently selected for output based on the signal switching signal.

According to the optical sensor with a signal processing function of the fifth embodiment, the signal processing circuit at the subsequent stage uses the output of the desired lookup table by supplying the signal switching signal to the signal selection circuit 50. So you can
The range of application expands.

[0052]

As described in detail above, according to the present invention,
The processing performed by the subsequent signal processing circuit can be simplified, and the dynamic range can be widened.
Further, it is possible to provide an optical sensor with a signal processing function that can directly use components used in a conventional signal processing circuit.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of an optical sensor with a signal processing function according to Embodiment 1 of the present invention.

FIG. 2 is a diagram illustrating a configuration example of a lookup table used in the optical sensor with a signal processing function according to the first embodiment of the present invention;

FIG. 3 is a diagram showing an example of conversion of output characteristics performed by the optical sensor with a signal processing function according to the first embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of an optical sensor with a signal processing function according to Embodiment 2 of the present invention.

FIG. 5 is a diagram illustrating an example of conversion of output characteristics performed by an optical sensor with a signal processing function according to a second embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of an optical sensor with a signal processing function according to Embodiment 3 of the present invention.

FIG. 7 is a diagram illustrating an example of conversion of output characteristics performed by an optical sensor with a signal processing function according to a third embodiment of the present invention.

FIG. 8 is a block diagram showing a configuration of an optical sensor with a signal processing function according to Embodiment 4 of the present invention.

FIG. 9 is a block diagram showing a configuration of an optical sensor with a signal processing function according to Embodiment 5 of the present invention.

FIG. 10 is a diagram showing a general circuit configuration of a conventional optical sensor.

FIG. 11 is a diagram showing output characteristics of a conventional optical sensor.

[Description of Signs] 10 Optical sensor 11 A / D converter 12, 20 Look-up table 13 Memory 30 First look-up table 31 Second look-up table 40, 50 Signal selection circuit

Claims (8)

[Claims] 1. When the illuminance of incident light is equal to or less than a first predetermined value, a signal indicating a linear output characteristic is output. An optical sensor that outputs a signal; and a characteristic conversion unit that converts the signal output from the optical sensor into a signal indicating a logarithmic output characteristic according to the illuminance of the incident light and outputs the signal as a sensor signal. Optical sensor with signal processing function. 2. An A / D converter for converting an analog signal from the optical sensor into a digital signal, wherein the characteristic converter converts the digital signal output from the A / D converter into incident light. The optical sensor with a signal processing function according to claim 1, wherein the optical sensor has a signal processing function, and converts the signal into a signal indicating logarithmic output characteristics according to the illuminance and outputs the signal as a sensor signal. 3. The optical sensor with a signal processing function according to claim 1, wherein said characteristic conversion means is a look-up table. 4. The characteristic conversion means according to claim 1, wherein a range of a signal output when the illuminance of the incident light is equal to or smaller than a second predetermined value, and a range of a signal output when the illuminance of the incident light is larger than the second predetermined value. The optical sensor with a signal processing function according to any one of claims 1 to 3, wherein the optical sensor is converted so as to overlap and outputs the sensor signal as a sensor signal. 5. A sensor signal output from said characteristic converting means, which is a signal when the illuminance of said incident light is equal to or less than said second predetermined value or a signal when said illuminance is larger than said second predetermined value. The optical sensor with a signal processing function according to claim 4, further comprising an identification signal output unit that outputs an identification signal for identifying. 6. The characteristic conversion unit, wherein the first conversion unit converts a signal output from the optical sensor when the illuminance of the incident light is within a first range, and the illuminance of the incident light. And a second conversion unit that converts a signal output from the optical sensor when illuminance falls within a second range. The first conversion unit and the second conversion unit each output The optical sensor with a signal processing function according to any one of claims 1 to 3, wherein the signal is converted so that the ranges of the signals to be output overlap each other and output. 7. An identification signal output means for outputting an identification signal for identifying whether a signal is output from the first conversion means or a signal output from the second conversion means. An optical sensor with a signal processing function according to claim 6. 8. The apparatus according to claim 6, further comprising signal selection means for selecting one of a signal output from said first conversion means and a signal output from said second conversion means.
An optical sensor with a signal processing function according to item 1.