JP2017201275A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus which can precisely measure the temperature of an imaging element.SOLUTION: An imaging apparatus 1 includes: an imaging element 11 for outputting an imaging signal in synchronization with an imaging clock signal; a cooling section 12 for cooling the imaging element 11; an AD converter 14 for converting a temperature signal showing the temperature of the imaging element 11 into a digital signal and outputting the digital signal in synchronization with the AD clock signal; and a controller 16 for controlling the cooling operation of the cooling section 12 on the basis of an average value obtained by equalizing the value of the digital signal output from the AD converter 14 over a specific time. The ratio of cycles of the clock signal and the AD clock signal is represented by a pair of relatively prime numbers.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging apparatus.

  An imaging device having an imaging device having sensitivity in the near infrared region (1000 to 2500 nm) can acquire an image showing the absorption and reflection distribution of light in the near infrared region. It is used when discriminating components. In particular, an imaging device having sensitivity at a wavelength of 1700 nm or more has a large dark current at room temperature, and therefore needs to be operated at a low temperature using a cooling mechanism such as a Peltier cooler or a Stirling cooler. Further, when such an image sensor is operated at a low temperature, the dark current varies depending on the temperature of the image sensor, and the image signal obtained from the image sensor also varies. Therefore, it is necessary to measure the temperature of the image sensor with high accuracy and control the temperature of the image sensor with high accuracy (see Patent Document 1).

Special table 2003-532111 gazette

  In the imaging apparatus as described above, the temperature of the imaging element may not be measured with high accuracy. As a result, the temperature control of the image sensor becomes unstable, the dark current varies, and the image signal obtained from the image sensor may also vary.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an imaging apparatus capable of measuring the temperature of the imaging element with high accuracy.

  An imaging device of the present invention converts an imaging element that outputs an imaging signal in synchronization with an imaging clock signal, a cooling unit that cools the imaging element, and a temperature signal indicating the temperature of the imaging element into a digital signal, AD converter that outputs a digital signal in synchronization with an AD clock signal, and cooling of the cooling unit based on an average value obtained by averaging the value of the digital signal output from the AD converter over a certain period of time A control unit that controls the operation, and the ratio of the periods of the imaging clock signal and the AD clock signal is expressed by a set of prime numbers.

  The imaging apparatus of the present invention can measure the temperature of the imaging element with high accuracy.

FIG. 1 is a block diagram illustrating a configuration of the imaging apparatus 1. FIG. 2 is a timing chart of each signal in the comparative example. FIG. 3 is a timing chart of each signal in the present embodiment.

  An imaging device of the present invention converts an imaging element that outputs an imaging signal in synchronization with an imaging clock signal, a cooling unit that cools the imaging element, and a temperature signal indicating the temperature of the imaging element into a digital signal, AD converter that outputs a digital signal in synchronization with an AD clock signal, and cooling of the cooling unit based on an average value obtained by averaging the value of the digital signal output from the AD converter over a certain period of time A control unit that controls the operation, and the ratio of the periods of the imaging clock signal and the AD clock signal is expressed by a set of prime numbers.

  In the present invention, it is preferable that the imaging element has sensitivity to light having a wavelength of 1000 to 2500 nm. In addition, it is preferable that the period of each of the imaging clock signal and the AD clock signal is variable while the ratio of the period of the imaging clock signal and the AD clock signal is kept constant.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. The present invention is not limited to these exemplifications, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

  FIG. 1 is a block diagram illustrating a configuration of the imaging apparatus 1. This figure mainly shows a configuration relating to cooling of the image sensor 11. The imaging device 1 includes an imaging element 11, a cooling unit 12, an amplification unit 13, an AD conversion unit 14, a temperature conversion unit 15, and a control unit 16.

  The imaging element 11 outputs an imaging signal in synchronization with the imaging clock signal according to the incidence of light. The image sensor 11 is sensitive to light having a wavelength of 1000 to 2500 nm. The image sensor 11 has a temperature sensing unit that outputs a temperature signal indicating the temperature. The cooling unit 12 cools the image sensor 11 and includes, for example, a Peltier cooler, a Stirling cooler, and the like. The amplifying unit 13 amplifies the temperature signal.

  The AD conversion unit 14 receives the temperature signal amplified by the amplification unit 13, converts the temperature signal (analog signal) into a digital signal, and outputs the digital signal in synchronization with the AD clock signal. The temperature conversion unit 15 receives the digital signal output from the AD conversion unit 14, converts the digital signal into a signal that can be collated with the set temperature, and outputs the converted digital signal.

  The control unit 16 gives the imaging device 11 an imaging clock signal that determines the output timing of the imaging signal from the imaging device 11. The control unit 16 provides the AD conversion unit 14 with an AD clock signal that determines the output timing of the digital signal from the AD conversion unit 14. The control unit 16 receives the digital signal output from the temperature conversion unit 15, averages the value of the digital signal over a predetermined time, obtains an average value, and cools by the cooling unit 12 based on the average value. Control the behavior. The control unit 16 causes the temperature of the image sensor 11 to be within the target value or the target range by such feedback control.

  FIG. 2 is a timing chart of each signal in the comparative example. In this figure, (a) an imaging clock signal, (b) a temperature signal, and (c) an AD clock signal are shown. In this comparative example, the imaging clock signal and the AD clock signal have the same period and the same phase. In general, a signal line that transmits an imaging clock signal input to the image sensor 11 and a signal line that transmits a temperature signal output from the image sensor 11 are arranged in parallel to each other. For this reason, noise of a pattern corresponding to the period of the imaging clock signal is easily superimposed on the temperature signal output from the imaging element 11.

  For example, as shown in FIG. 2B, spikes may be observed in the temperature signal at the rising timing and falling timing of the imaging clock signal. When the imaging clock signal and the AD clock signal are synchronized with each other, a digital signal having a spike portion value of the temperature signal is always output from the AD conversion unit 14. The digital signal output from the AD conversion unit 14 does not indicate a true temperature value (a value at a portion where there is no spike), but is obtained by adding an offset to the true temperature value.

  If this offset is 1LSB or more of the digital signal, the effect remains after AD conversion, and an error occurs in temperature reading. In addition, such pattern noise may fluctuate every time reading is performed, and the reading error may also fluctuate, resulting in unstable temperature control.

  FIG. 3 is a timing chart of each signal in the present embodiment. This figure shows (a) a clock source signal, (b) an imaging clock signal, (c) a temperature signal, and (d) an AD clock signal. In the present embodiment, the ratio of the periods of the imaging clock signal and the AD clock signal is represented by a set of relatively prime numbers.

  Each of the imaging clock signal and the AD clock signal is preferably generated by dividing the clock source signal. A frequency division ratio when the clock source signal is divided to generate the imaging clock signal is M, and a frequency division ratio when the clock source signal is divided to generate the AD clock signal is N. At this time, the frequency division ratios M and N are set so as not to have a common factor as much as possible. It is desirable that the frequency division ratios M and N are relatively prime. However, if this is difficult due to control restrictions, M = aM ′, N = aN ′ (M ′ and N ′ are different prime natural numbers, a is an arbitrary natural number), and a is as small as possible. Set as follows. In FIG. 3, M ′ = 7, N ′ = 8, and a = 1.

  When changing the frame rate, it is preferable to change the period of each of the imaging clock signal and the AD clock signal while maintaining a constant ratio of the period of the imaging clock signal and the AD clock signal.

  In the present embodiment, as indicated by a thick arrow in FIG. 3C, the value of the digital signal output from the AD conversion unit 14 in synchronization with the AD clock signal partially increases or decreases due to the influence of noise. However, in the time range longer than aM'N 'times the period of the clock source signal, the deviation of the digital signal value is alleviated. Therefore, even if there is an influence of noise on the temperature signal, the control unit 16 can know the true temperature by using the average value of the reading values over the time.

  DESCRIPTION OF SYMBOLS 1 ... Imaging device, 11 ... Imaging element, 12 ... Cooling part, 13 ... Amplifying part, 14 ... AD conversion part, 15 ... Temperature conversion part, 16 ... Control part.

Claims (3)

An image sensor that outputs an imaging signal in synchronization with an imaging clock signal;
A cooling unit for cooling the image sensor;
An AD converter that converts a temperature signal indicating the temperature of the image sensor into a digital signal and outputs the digital signal in synchronization with an AD clock signal;
A control unit that controls the cooling operation of the cooling unit based on an average value obtained by averaging the value of the digital signal output from the AD conversion unit over a certain period of time;
With
A ratio of the periods of the imaging clock signal and the AD clock signal is represented by a set of prime numbers.
Imaging device. The image sensor has sensitivity to light having a wavelength of 1000 to 2500 nm.
The imaging device according to claim 1. The period of each of the imaging clock signal and the AD clock signal is variable while maintaining a constant ratio of the period of the imaging clock signal and the AD clock signal.
The imaging device according to claim 1 or 2.

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