JP2013011449A - Light sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light sensor capable of quickening responsibility.SOLUTION: A control part 30 for converting a sensor signal into a digital signal has comparison means 32 for comparing a sensor signal with a prescribed threshold, processing means 33 for outputting an AD conversion start signal on the basis of the comparison result of the comparison means 32 and first AD conversion means 31 for converting the sensor signal into a first digital signal. The control part 30 makes the processing means 33 input a sensor signal at the time when a prescribed period during which a light receiving element has been exposed has elapsed from an output control circuit to the comparison means 32. On the basis of the comparison result of the comparison means 32, the control part 30 makes the processing means 33 input the AD conversion start signal in the first AD conversion means 31 so as to convert the sensor signal into a first digital signal when the sensor signal is equal to or more than the threshold, while it makes the output control circuit extend an output period of the light receiving element and makes the processing means 33 input the sensor signal at the time when the extension period has elapsed in the comparison means 32 when the sensor signal is less than the threshold. Thus, processing on the basis of the comparison result of the comparison means 32 is performed.

Description

  The present invention relates to a light sensor that converts a sensor signal of an analog signal output from a sensor unit into a digital signal and outputs the digital signal.

  Conventionally, a sensor unit that outputs a sensor signal that is an analog signal according to an exposure amount, a light receiving element driving circuit that controls an exposure period of the sensor unit, a signal processing circuit that has an AD conversion circuit, and a lower limit value are set. A light sensor including a comparator is disclosed (for example, see Patent Document 1). The exposure amount is obtained by the product of the illuminance of the measurement light detected by the sensor unit and the exposure period. When the measurement light is sunlight, the illuminance is considered to be constant in local time. Therefore, it increases in proportion to the exposure period.

  In such a light sensor, when the sensor unit is exposed to the measurement light for a predetermined period, the sensor unit outputs a sensor signal that is an analog signal corresponding to the exposure amount. The sensor signal is input to the signal processing circuit and the comparator, and the comparator compares the sensor signal with the lower limit value. The lower limit is arbitrarily set, and is set to a value at which the ratio between the sensor signal and noise, that is, the SN ratio becomes sufficiently large. When the sensor signal is larger than the lower limit value, the signal processing circuit converts the sensor signal into a digital signal. When the sensor signal is smaller than the lower limit value, the exposure period of the sensor unit is set again so that the sensor signal becomes larger than the lower limit value in the light receiving element driving circuit, and the sensor unit is exposed for a predetermined period of time. After that, the sensor signal output from the sensor unit is converted into a digital signal by the signal processing circuit.

Japanese Patent Laid-Open No. 08-247847

  However, in the above light sensor, when the sensor signal is smaller than the lower limit value, the exposure period is reset, and the sensor unit is exposed again for the predetermined period, and then the sensor signal is converted into a digital signal. There is a problem of getting worse.

  An object of this invention is to provide the light sensor which can make responsiveness quick in view of the said point.

  In order to achieve the above object, according to the first aspect of the present invention, the light receiving element (11) for outputting an electrical signal corresponding to the exposure amount, and the output period of the light receiving element (11) are controlled so that the electric power at a predetermined time is obtained. An output control circuit (12) that outputs an analog signal as a sensor signal that is an analog signal, and a control unit (30) that converts the sensor signal that is an analog signal into a digital signal. It is characterized by the following points.

  That is, the control unit (30) receives the sensor signal, and outputs the AD conversion start signal based on the comparison result of the comparison unit (32) that compares the sensor signal with a predetermined threshold, and the comparison unit (32). A processing unit (33); and a first AD conversion unit (31) that converts the sensor signal into a first digital signal when an AD conversion start signal is input from the processing unit (33). ing. Then, the processing means (33) causes the output control circuit (12) to input the electrical signal when the predetermined period has elapsed when the light receiving element (11) outputs for a predetermined period to the comparison means (32) as a sensor signal, and to compare Based on the comparison result of the means (32), when the sensor signal is equal to or greater than the threshold value, the AD conversion start signal is input to the first AD conversion means (31) to convert the sensor signal into the first digital signal, and the sensor signal is less than the threshold value. In this case, the output period of the light receiving element (11) is extended to the output control circuit (12), and an electrical signal at the time when the extension period has elapsed is input to the comparison means (32), and based on the comparison result of the comparison means (32). It is characterized by performing the processing.

  In such a light sensor, after outputting (exposure) the light receiving element (11) for a predetermined period, when the sensor signal is less than the threshold value, the output period of the light receiving element (11) is extended and the light receiving element (11) is left as it is. Output (exposure) is continued. And after the extended period passes, the process based on the comparison result of the comparison means (32) is performed again. For this reason, when the exposure amount of the sensor part is smaller than the lower limit value, the exposure period when the sensor signal is less than the threshold value is effective compared to the conventional one in which the exposure period is reset and the sensor part is exposed again. It can be used for quick response.

  In this case, as in the second aspect of the invention, the second digital signal indicating the exposure amount for the predetermined output period is sent to the control unit (30) according to the output period of the light receiving element (11). 2nd AD conversion means (33) which converts into (3) can be provided.

  According to this, the first digital signal converted by the first AD conversion means (31) is exposed by the second AD conversion means (33) for a predetermined output (exposure) period according to the output period of the light receiving element (11). Since it can convert into the 2nd digital signal which shows quantity, it can suppress making the structure of the side by which the output signal from a light sensor is input complicated.

  Further, as in the invention described in claim 3, the second AD conversion means (33) is arranged on the most significant bit side or / and the least significant bit side of the first digital signal according to the output period of the light receiving element (11). By adding 0, it can be converted into a second digital signal indicating the exposure amount for a predetermined output period.

In this way, by adding 0 to the most significant bit side or / and the least significant bit side of the first digital signal, the first digital signal is set to a value of 1/2 ⁿ (n = 0, 1, 2,...). Can be converted to a second digital signal.

  Further, as in the invention described in claim 4, the threshold value is set to a value that is ½ of the maximum value that can be taken by the sensor signal input to the comparison means (32), and the processing means (33) If it is less, the output control circuit (12) causes the output period of the light receiving element (11) to be doubled, and the processing based on the comparison result of the comparison means (32) when the extension period has elapsed is performed. be able to.

  According to this, when the sensor signal is converted into the first digital signal by the first AD conversion means (31), it can be suppressed that the sensor signal is a saturated signal, and the detection accuracy can be prevented from being lowered. be able to.

Further, as in the invention described in claim 5, the second AD conversion means (33) is a case where the sensor signal after extending the output period of the light receiving element (11) is less than the threshold value, and the most significant bit side When the total number that can add 0 to the least significant bit side is n, the initial output period of the light receiving element (11) is T, and the output period of the light receiving element (11) is 2 ⁿ T, the sensor Even if the signal is less than the threshold value, the sensor signal at that time can be converted into the first digital signal by the first AD conversion means (31).

  Further, as in the invention described in claim 6, an amplification means connected to the light receiving element (11) is provided, and the first AD conversion means (31) and the comparison means (32) are amplified by the amplification means. A sensor signal can be input.

  And like invention of Claim 7, the light sensor as described in any one of Claim 1 thru | or 6 shall be used mounted in a vehicle and shall be used for detecting sunlight. be able to.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is a block diagram of the light sensor in a 1st embodiment of the present invention. It is a circuit diagram of the sensor part shown in FIG. It is a timing chart which shows the action | operation of a sensor part. It is a timing chart which shows the relationship between a sensor signal and the output period of a light receiving element. It is a figure which shows the relationship between the output period of a light receiving element, and a 2nd digital signal. It is a flowchart of the program which a microcomputer performs.

(First embodiment)
A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a light sensor in the present embodiment. The light sensor of this embodiment is preferably mounted on a vehicle and used to detect sunlight.

  As shown in FIG. 1, the light sensor includes a sensor unit 10 that outputs an analog sensor signal corresponding to the exposure amount and a control unit 30 that converts the sensor signal into a digital signal. The exposure amount is obtained by the product of the illuminance of the measurement light detected by the light receiving element described later and the exposure period. When the measurement light is sunlight, the illuminance is constant in local time. Therefore, it increases in proportion to the exposure period.

  First, the configuration of the sensor unit 10 will be described. FIG. 2 is a circuit diagram of the sensor unit 10 in the present embodiment. As shown in FIG. 2, the sensor unit 10 receives a reset signal or an output control signal from the light receiving element 11 configured by a photodiode or the like that outputs an electrical signal corresponding to the exposure amount, and the control unit 30. And an output control circuit 12 for controlling the output of the light receiving element 11.

  The output control circuit 12 includes P-channel type first to fourth PMOS transistors (hereinafter simply referred to as first to fourth transistors) 13 to 16, first, second, and fourth transistors 13, 14, And a drive circuit 17 connected to the 16 gate terminals and configured to input drive signals RST, TG, and BIAS to control on / off of the first, second, and fourth transistors 13, 14, and 16.

  The first transistor 13 has a source terminal connected to the light receiving element 11 and a drain terminal of the second transistor 14. The drain terminal of the first transistor 13 is connected to the ground. The source terminal of the second transistor 14 is connected to the gate terminal of the third transistor 15. The third transistor 15 has a drain terminal connected to the ground and a source terminal connected to the drain terminal of the fourth transistor 16. The fourth transistor 16 has a source terminal connected to the power supply 18. A connection point between the source terminal of the third transistor 15 and the drain terminal of the fourth transistor 16 is connected to the terminal 19, and a sensor signal is output from the terminal 19. The drive circuit 17 is connected to the terminal 20 and inputs the drive signals RST, TG, and BIAS to the first, second, and fourth transistors 13, 14, and 16 in accordance with signals from the control unit 30. ing. Note that the third transistor 15 functions as an amplifier having an amplification factor of 1, and the fourth transistor 16 functions as a constant current element for driving the third transistor 15.

  Next, the operation of the sensor unit 10 will be described. FIG. 3 is a timing chart showing the operation of the sensor unit 10. During the period when the sensor unit 10 is operating, the drive circuit 17 inputs a low signal as the control signal BIAS and always turns on the fourth transistor 16. In the following, as shown in FIG. 2, the connection point between the source terminal of the first transistor 13 and the second transistor 14 is the point A, and the connection between the drain terminal of the second transistor 14 and the gate terminal of the third transistor 15. The point will be described as point B.

  First, when a reset signal is input from the control unit 30 at time T0, the sensor unit 10 inputs a low signal as the control signal RST from the drive circuit 17 in order to reset the charge of the light receiving element 11, and the first transistor 13 Is turned on, and the charge accumulated in the light receiving element 11 is discharged to the ground. At this time, if the second transistor 14 is off, the potential at the point B becomes indeterminate and the sensor signal becomes indefinite. Therefore, the low signal is input from the drive circuit 17 as the control signal TG, and the second transistor 14 is also turned on. To do.

  Subsequently, at time T1, an output (exposure) start signal is input from the control unit 30, a high signal is input from the drive circuit 17 as the drive signal RST, and the first transistor 13 is turned off. As a result, after the time point T1, charges corresponding to the exposure amount are accumulated in the light receiving element 11, and the potential at the point A becomes higher according to the exposure amount. At this time, by keeping the control signal TG of the drive circuit 17 as a low signal and maintaining the ON state of the second transistor 14, the potentials at the points A and B become the same potential. Therefore, since the third transistor 15 functions as an amplifier having an amplification factor of 1, the potential (voltage) at point A is output from the terminal 19 as a sensor signal.

  Then, after the time T2, that is, after a lapse of a predetermined period from the time T1, the first output control signal is input from the control unit 30, the high signal is input as the drive signal TG from the drive circuit 17, and the second transistor 14 is turned off. . As a result, the point A and the point B are electrically separated, so that the potential at the point B is maintained at the potential at the time T2 after the time T2. That is, this voltage is output as a sensor signal after time T2. Note that the potential at the point A increases in accordance with the exposure period after the time T2. That is, the output (exposure) period of the light receiving element 11 is a period during which the potential at the point A is output from the terminal 19, and in FIG. 3 is a period from the time point T1 to the time point T2.

  After that, at time T3, similarly to time T0, a reset signal is input from the control unit 30, and a low signal is input from the drive circuit 17 as the drive signals RST and TG to turn on the first and second transistors 13 and 14. The charge accumulated in the light receiving element 11 is discharged to the ground.

  Specifically, as will be described later, the control unit 30 performs the threshold determination of the sensor signal during the period from the time point T2 to the time point T3. When the sensor signal is less than the threshold value, the second output control signal is sent to the sensor unit 10. input. Then, a low signal is input as a drive signal TG from the drive circuit 17 to turn on the second transistor 14, and the potential at the point B is again made equal to the potential at the point A. After that, after a predetermined period, the first output control signal is input to the sensor unit 10 again, a high signal is input as the drive signal TG, the second transistor 14 is turned off, and the potential at the point B is changed from the time T1 to the time T2. Thereafter, the potential is maintained at a potential corresponding to an output (exposure) period of the light receiving element 11 after a predetermined period. Then, the threshold determination of the sensor signal is performed again. That is, the time T3 is variable, and the operation after the time T3 is performed after the control unit 30 performs threshold determination of the sensor signal and converts the sensor signal into a digital signal.

  As shown in FIG. 1, the control unit 30 includes an AD converter 31, a comparator 32, and a microcomputer (hereinafter simply referred to as a microcomputer) 33. In the present embodiment, the AD converter 31 corresponds to the first AD conversion means of the present invention, the comparator 32 corresponds to the comparison means of the present invention, and the microcomputer 33 includes the processing means and the second AD of the present invention. It corresponds to the conversion means.

  The AD converter 31 is connected to the sensor unit 10 and the microcomputer 33. When an AD conversion start signal is input from the microcomputer 33, the AD converter 31 converts the sensor signal into a first digital signal and converts the first digital signal into the microcomputer 33. Output to. Although not particularly limited, in this embodiment, the sensor signal is converted into a 10-bit first digital signal and output to the microcomputer 33.

  The comparator 32 is connected to the sensor unit 10 and the microcomputer 33, and receives a sensor signal from the sensor unit 10, and also receives a voltage as a threshold value divided by the resistors R1 and R2 from the reference voltage Vref. Then, a comparison signal corresponding to the magnitude of the sensor signal and the threshold value is output to the microcomputer 33. In the present embodiment, the reference voltage Vref is set equal to the maximum value of the sensor signal input to the comparator 32, that is, the saturation signal. Further, the resistor R1 and the resistor R2 are equal to each other, and a voltage that is ½ of the reference voltage is input as a threshold value.

  The microcomputer 33 has a RAM, a ROM, etc. (not shown) and executes a stored program. Specifically, the reset signal, the output (exposure) start signal, the first and second output control signals are output to the output control circuit 12, and the first output control signal is output to the output control circuit 12 (FIG. 3). Among them, the magnitude of the sensor signal and the threshold is determined based on the comparison result of the comparator 32 at time T2). When the sensor signal is equal to or greater than the threshold value, an AD conversion start signal is input to the AD converter 31 to convert the sensor signal into a first digital signal. When the first digital signal is input, the first digital signal is converted into the first digital signal. It converts into the 2nd digital signal according to the output (exposure) period of the light receiving element 11, and outputs it. When the sensor signal is less than the threshold value, a second output control signal is output to the output control circuit 12 to extend the output (exposure) period of the light receiving element 11, and the first output is again output to the output control circuit 12 after a predetermined period. A control signal is output to determine the magnitude of the sensor signal and the threshold value, and processing based on the determination result is performed. In addition, extending the output (exposure) period of the light receiving element 11 means, in other words, continuing the output (exposure) of the light receiving element 11 as it is, and resetting the output (exposure) period of the light receiving element 11 again. is not.

  Next, a method in which the microcomputer 33 converts the first digital signal into the second digital signal according to the output (exposure) period of the light receiving element 11 will be described. When the microcomputer 33 determines that the sensor signal is equal to or greater than the threshold value, the microcomputer 33 determines the most significant bit (hereinafter simply referred to as MSB) side and / or the highest digital signal based on the output (exposure) period of the light receiving element 11. 0 is added to the lower bit (hereinafter, simply referred to as LSB) side to convert it into a 15-bit second digital signal. For example, by adding 5 0s to the LSB side, the first digital signal can be converted to a 2nd digital signal of the same size (1 time), and one 0 is added to the MSB side and the LSB side By adding four zeros to the first digital signal, it is possible to convert the first digital signal to a second digital signal having a half value. Two zeros are added to the MSB side and three zeros are added to the LSB side. Thus, the first digital signal can be converted into a second digital signal having a value of ¼. Then, by adding three 0s on the MSB side and adding two 0s on the LSB side, the first digital signal can be converted into a second digital signal having a value of 1/8, and 0 on the MSB side. The first digital signal can be converted to a second digital signal having a value of 1/16 by adding four 0s and one 0 on the LSB side, and adding five 0s on the MSB side Thus, the first digital signal can be converted into a second digital signal having a value of 1/32.

That is, the microcomputer 33 of the present embodiment has an output (exposure) period of 2 for the light receiving element 11 when T is an output (exposure) period for the light receiving element 11 when the magnitude of the sensor signal and the threshold value is first determined. The first digital signal when ⁿ T (n = 0 to 5) is converted into a second digital signal indicating the exposure amount when the output (exposure) period of the light receiving element 11 is T.

  FIG. 4 is a timing chart showing the relationship between the sensor signal and the output (exposure) period of the light receiving element 11. In FIG. 4, Vcc is the maximum value that can be taken by the sensor signal, and the threshold value is ½ Vcc. Further, in FIG. 4, offset, noise, and the like are ignored.

  Consider the case where sensor signals 1 to 4 are input to the AD converter 31 and the comparator 32 as shown in FIG. As described above, the sensor signal depends on the output (exposure) period of the light receiving element 11. In this case, for example, at time T, the sensor signals 1 to 4 can be converted into digital signals. However, since the sensor signals 2 to 4 do not exceed the threshold value and the SN ratio is small, the sensor signals 2 to 4 are reduced. Even if it is converted into a digital signal, the detection accuracy is low. On the other hand, at the time 32T, the outputs of the sensor signals 1 to 4 all exceed the threshold value, but the sensor signals 1 to 3 cannot be accurately detected because the sensor signals 1 to 3 are saturated. Even if 3 is converted into a digital signal, the detection accuracy is low.

Then, as described above, the microcomputer 33 adds 0 to the MSB side and / or the LSB side, thereby making the first digital signal 1 ×, 1/2 ×, 1/4 ×, 1/8 ×, It can be converted into a second digital signal having a value of / 16 times or 1/32 times. Therefore, the microcomputer 33 of the present embodiment causes the AD converter 31 to convert the sensor signal into the first digital signal when the sensor signal exceeds the threshold at the time of 2 ⁿ T (n = 0 to 5), The first digital signal is converted into a second digital signal in the output (exposure) period T of the light receiving element 11.

  FIG. 5 is a diagram showing the relationship between the output (exposure) period of the light receiving element 11 and the structure of the second digital signal. In FIG. 5, AD (15) indicates that the second digital signal is 15 bits, and AD (10) indicates the 10-bit first digital signal. As shown in FIGS. 4 and 5, for example, in the case of the sensor signal 2, since the sensor signal does not exceed the threshold value at the time point T, the microcomputer 33 converts the sensor signal to the AD converter at the time point 2T. In step 31, the first digital signal is converted. Then, one 0 is added to the MSB side with respect to the first digital signal and four 0s are added to the LSB side to convert the first digital signal into a second digital signal having a value half that of the first digital signal. That is, the microcomputer 33 converts the first digital signal into a second digital signal indicating the exposure amount when the output (exposure) period of the light receiving element 11 is T.

  Further, for example, in the case of the sensor signal 3, the sensor signal does not exceed the threshold at time T, time 2T, and time 4T. For this reason, the microcomputer 33 converts the sensor signal into the first digital signal at the time point 8T by the AD converter 31, and adds three 0s to the MSB side and 0 to the LSB side with respect to the first digital signal. Are converted into a second digital signal having a value 1/16 of the first digital signal. That is, the microcomputer 33 converts the first digital signal into a second digital signal indicating the exposure amount when the output (exposure) period of the light receiving element 11 is T.

Note that the threshold value of the comparator 32 of the present embodiment is set to a value that is ½ of the maximum value that the sensor signal can take, as described above, the microcomputer 33 has an output (exposure) period of the light receiving element 11. This is because if the first digital signal is 2 ⁿ T, the first digital signal can be converted into a second digital signal indicating the exposure amount when the output (exposure) period is T. That is, when the sensor signal is less than the threshold value, the sensor signal does not saturate even after the output (exposure) period of the light receiving element 11 has doubled from that point, and an accurate exposure amount can be detected. It is.

  Next, the operation of such a light sensor will be described. FIG. 6 is a flowchart of a program executed by the microcomputer 33 of the light sensor in the present embodiment. For example, when the microcomputer 33 is mounted on a vehicle and used, when the ignition switch is turned on and a request signal for requesting the illuminance of external light is input, the microcomputer 33 executes the following control.

  As shown in FIG. 6, in step 100, a reset signal is input to the output control circuit 12 (time T0 in FIG. 2), and the light receiving element 11 is reset. Specifically, as described above, a low signal is input as the control signals RST and TG from the drive circuit 17 to release the charge accumulated in the light receiving element 11.

  In step 101, an output (exposure) start signal is input to the output control circuit 12 (time T1 in FIG. 2), and a high signal is input from the drive circuit 17 as the control signal RST to receive the potential at point A in FIG. A potential corresponding to the exposure amount of the element 11 is set and the potential at point B in FIG. 2 is made equal to the potential at point A. As a result, a sensor signal corresponding to the exposure amount of the light receiving element 11 is input from the sensor unit 10 to the AD converter 31 and the comparator 32. The microcomputer 33 measures the exposure period of the light receiving element 11.

  Subsequently, after the light receiving element 11 is exposed for a predetermined period T as a period t (step 102), in step 103, a first output control signal is input to the output control circuit 12 (time point T2 in FIG. 2). Then, a high signal is input as the control signal TG from the drive circuit 17 to maintain the potential at the point B at a potential corresponding to the exposure amount during the exposure period T of the light receiving element 11. In this state, the magnitude of the sensor signal input to the comparator 32 and the threshold value is determined. If the sensor signal is less than the threshold value, the process proceeds to step 104. If the sensor signal is greater than or equal to the threshold value, the process proceeds to step 106.

  In step 104, it is determined whether the exposure period t of the light receiving element 11 is less than 32T. The microcomputer 33 in the present embodiment converts a 10-bit first digital signal into a 15-bit second digital signal by adding 0 to the MSB side and / or LSB side, and at most 0 to the MSB side. Are added to convert the first digital signal into a second digital signal having a value of 1/32. That is, when the output (exposure) period of the light receiving element 11 is 32T or more, the microcomputer 33 indicates the exposure amount when the output (exposure) period of the light receiving element 11 is T. It cannot be converted to the second digital signal. For this reason, even if the sensor signal is less than the threshold, if the exposure period is 32T or more, the process proceeds to step 106. In other words, step 104 is a step for determining whether or not the exposure period t of the light receiving element 11 is 32T.

  If it is determined in step 104 that the output (exposure) period of the light receiving element 11 is less than 32T, the process proceeds to step 105, and the output (exposure) period t of the light receiving element 11 in step 102 is doubled. The output (exposure) of the light receiving element 11 is continued. That is, for example, if the output (exposure) period t of the light receiving element 11 in step 102 is T, the output (exposure) period of the light receiving element 11 is set to 2T, and the sensor signal when performing the determination in step 103 is received. A signal when the output (exposure) period of the element 11 is 2T is set. When the output (exposure) period t of the light receiving element 11 in step 102 is 2T, the output (exposure) period of the light receiving element 11 is set to 4T, and the sensor signal when performing the determination in step 103 is the light receiving element 11. This is a signal when the output (exposure) period is 4T. Specifically, as described above, the second output control signal is input to the output control circuit 12, and a low signal is input from the drive circuit 17 as the control signal TG, so that the potential at the point B is equal to the potential at the point A. . Then, after the extension period has elapsed, the first output control signal is input to the output control circuit 12 again, and the determination in step 103 is performed.

  In step 106, an AD conversion start signal is input to the AD converter 31, the sensor signal is converted into a first digital signal, and the first digital signal is input to the microcomputer 33. In the present embodiment, the first digital signal is a 10-bit digital signal.

  Subsequently, in step 107, the first digital signal input from the AD converter 31 is converted into a second digital signal in accordance with the output (exposure) period t of the light receiving element 11. For example, when the output (exposure) period t of the light receiving element 11 is T, the first digital signal is converted into a second digital signal obtained by adding five 0s to the LSB side, and the output (exposure) of the light receiving element 11 When the period is 2T, the first digital signal is converted into a second digital signal in which one 0 is added to the MSB side and four 0s are added to the LSB side. That is, the first digital signal is converted into a second digital signal indicating an exposure amount when the light receiving element 11 is output (exposed) for a predetermined period T. In step 108, the 15-bit second digital signal is output to the external circuit.

  As described above, in this embodiment, when the sensor signal is less than the threshold value, the output (exposure) period of the light receiving element 11 is extended as it is. In other words, when the exposure amount of the sensor unit is smaller than the lower limit value, the exposure period when the exposure amount is less than the threshold value is made effective compared to the conventional method in which the exposure period is reset and the exposure of the sensor unit is performed again. It can be used and responsiveness can be accelerated.

  Further, the microcomputer 33 adds 0 to the MSB side and / or the LSB side with respect to the first digital signal converted by the AD converter 31, thereby outputting the first digital signal to the output (exposure) period of the light receiving element 11. Since the second digital signal is converted according to T, the structure on the side where the second digital signal is input is not complicated.

(Other embodiments)
In the first embodiment, the configuration in which the sensor signal from the sensor unit 10 is directly input to the AD converter 31 and the comparator 32 has been described. For example, the sensor signal from the sensor unit 10 is predetermined by an amplifier as an amplifying unit. After the amplification, the amplified sensor signal may be input to the AD converter 31 and the comparator 32.

  In the first embodiment, an example in which a 10-bit first digital signal is converted into a 15-bit second digital signal and output has been described. For example, a 10-bit first digital signal is converted into a 20-bit first digital signal. Two digital signals may be converted. That is, the number of bits of the second digital signal can be appropriately changed by appropriately changing the number of zeros added to the MSB side and / or the LSB side. In the first embodiment, the example in which it is determined in step 104 whether or not the exposure period t is less than 32T has been described. For example, in the case where the second digital signal is 20 bits, in step 104. It can be determined whether or not the exposure period t is less than 1024T.

  Furthermore, in the first embodiment, the example in which the first digital signal is divided and converted into the second digital signal according to the output (exposure) period of the light receiving element 11 has been described. However, the output (exposure) of the light receiving element 11 Depending on the period, the first digital signal may be multiplied and converted to the second digital signal. That is, in the first embodiment, the example in which the second digital signal is a signal indicating the exposure amount when the output (exposure) period of the light receiving element 11 is T has been described, but for example, the second digital signal is received. A signal indicating the exposure amount when the output (exposure) period of the element 11 is 32T may be used.

  In the first embodiment, the threshold value of the comparator 32 is set to ½ of the maximum value that can be taken by the input sensor signal. When the sensor signal is less than the threshold value, the output (exposure) period of the light receiving element 11 However, the threshold and the output (exposure) extension period of the light receiving element 11 can be changed as appropriate.

  In the first embodiment, the microcomputer 33 has been described as including the processing means and the second AD conversion means of the present invention. For example, the microcomputer 33 includes only the processing means, and the second AD conversion means. Another AD converter for performing the above may be newly provided. Further, the microcomputer 33 may include the first AD conversion unit and the comparison unit of the present invention.

  In the first embodiment, the example in which the first digital signal is converted into the second digital signal in accordance with the output (exposure) period of the light receiving element 11 has been described. For example, the microcomputer 33 converts the first digital signal into the first digital signal. Alternatively, it may be output as it is without being converted into two digital signals. Even if such a light sensor is configured, the control unit 30 extends the output (exposure) period of the light receiving element 11 as it is when the sensor signal is less than the threshold value, so that the effect of the present invention can be obtained.

DESCRIPTION OF SYMBOLS 10 Sensor part 11 Light receiving element 12 Output control circuit 30 Control part 31 AD converter 32 Comparator 33 Microcomputer

Claims (7)

A light receiving element (11) for outputting an electrical signal corresponding to the exposure amount, and an output control for controlling the output period of the light receiving element (11) and outputting the electrical signal at a predetermined time as a sensor signal which is an analog signal. A sensor unit (10) having a circuit (12);
A controller (30) that converts the sensor signal, which is an analog signal, into a digital signal,
The control unit (30)
A comparison means (32) for receiving the sensor signal and comparing the sensor signal with a predetermined threshold;
Processing means (33) for outputting an AD conversion start signal based on the comparison result of the comparison means (32);
First AD conversion means (31) for converting the sensor signal into a first digital signal when the sensor signal is input and the AD conversion start signal is input from the processing means (33);
The processing means (33) provides the comparison means (32) with the electrical signal at the elapse of a predetermined period when the light receiving element (11) outputs to the output control circuit (12) as a sensor signal. Based on the comparison result of the comparison means (32), when the sensor signal is greater than or equal to the threshold value, the AD conversion start signal is input to the first AD conversion means (31) to input the sensor signal to the first signal. When the sensor signal is less than the threshold, the output control circuit (12) extends the output period of the light receiving element (11), and the electrical signal at the elapse of the extension period is converted to the sensor signal. The light sensor is inputted to the comparison means (32) and performs processing based on the comparison result of the comparison means (32).   The controller (30) includes second AD conversion means (33) for converting the first digital signal into a second digital signal indicating an exposure amount for a predetermined output period according to an output period of the light receiving element (11). The light sensor according to claim 1, wherein the light sensor is provided.   The second AD conversion means (33) adds the 0 to the most significant bit side or / and the least significant bit side of the first digital signal in accordance with the output period of the light receiving element (11), whereby the predetermined AD The light sensor according to claim 2, wherein the light sensor is converted into the second digital signal indicating an exposure amount with respect to an output period. The threshold value is a half value of the maximum value that can be taken by the sensor signal input to the comparison means (32).
The processing means (33), when the sensor signal is less than the threshold value, causes the output control circuit (12) to double the output period of the light receiving element (11), and when the extension period has elapsed, 4. The light sensor according to claim 3, wherein processing is performed based on a comparison result of the comparison means (32). The second AD conversion means (33) is a case where the sensor signal after extending the output period of the light receiving element (11) is less than the threshold value, and is 0 on the most significant bit side and the least significant bit side. Where n is the total number that can be added, and T is the first output period of the light receiving element (11), and when the output period of the light receiving element (11) is 2 ⁿ T, the sensor signal is the threshold value. 5. The light sensor according to claim 4, wherein the sensor signal at that time is converted into a first digital signal by the first AD conversion means (31) even if it is less than the value. Amplifying means connected to the sensor unit (10),
6. The sensor signal amplified by the amplifying means is input to the first AD converting means (31) and the comparing means (32). Light sensor. The light sensor according to any one of claims 1 to 6, wherein the light sensor is mounted on a vehicle and used to detect sunlight.

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