CN114034411A - Image sensor temperature measurement system and method - Google Patents
Image sensor temperature measurement system and method Download PDFInfo
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- CN114034411A CN114034411A CN202111327679.1A CN202111327679A CN114034411A CN 114034411 A CN114034411 A CN 114034411A CN 202111327679 A CN202111327679 A CN 202111327679A CN 114034411 A CN114034411 A CN 114034411A
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Abstract
The invention relates to the field of image sensor measurement, and discloses a system for measuring the temperature of an image sensor, which comprises a digital-to-analog converter, a comparator and an algorithm module, wherein the digital-to-analog converter, the comparator and the algorithm module are carried in the system; according to the invention, the digital-to-analog converter is improved, the thermometer current branch is introduced, the temperature measurement in the image sensor is realized, the measurement precision is high, a temperature detection module is not required to be designed independently, and the chip area is saved.
Description
Technical Field
The invention relates to the technical field of image sensors, in particular to a system and a method for measuring the temperature of an image sensor.
Background
The current mainstream sensors are all built-in with temperature detection modules. Typically, the temperature sensing module analog-to-digital converts either the thermometer current (IPTAT) or the thermometer Voltage (VPTAT) by a separate ADC (analog-to-digital converter). This method of directly measuring temperature by an independent ADC (analog-to-digital converter) inevitably occupies a certain chip area due to the addition of an ADC module, thereby increasing design cost.
Disclosure of Invention
The invention provides a system and a method for measuring the temperature of an image sensor, which do not increase an independent ADC (analog-to-digital converter) module, thereby realizing small area and low cost of a chip.
The invention is realized by the following technical scheme:
a system for image sensor temperature comprises a digital-to-analog converter, a comparator and an algorithm module which are carried in the system;
the digital-to-analog converter is used for generating a ramp signal, thermometer current is input to the input end of the digital-to-analog converter, and the thermometer current raises the voltage of the ramp signal by one voltage amplitude after passing through the digital-to-analog converter to generate voltage offset;
the comparator is used for comparing the ramp signal output by the digital-to-analog converter with the pixel signal, when the value of the ramp signal is equal to that of the pixel signal, the level of the comparator is inverted downwards, and when a new ramp signal is generated, the level of the comparator is inverted upwards;
the digital-to-analog converter is also internally provided with a counter, and the counter is used for starting counting when a ramp signal is generated and stopping counting when the comparator generates a falling edge; when the current of the thermometer flows into the digital-to-analog converter to generate a new ramp signal and raise the ramp signal by a voltage amplitude, the counter starts counting again, when the new ramp signal is equal to the value of the pixel signal again, the counter stops counting, and the output value of the counter for the second time subtracts the output value of the counter for the first time to obtain a CDS value;
and the algorithm module calculates the CDS value to obtain a thermometer current value input to the input end of the digital-to-analog converter, so that the temperature of the sensor is obtained.
As an optimization, the digital-to-analog converter further comprises a RAMP current source branch, a thermometer current branch and a gain control module, wherein the RAMP current source branch is used for generating a current with step change, the current generates a RAMP signal with step change after flowing through an effective resistor RES2, and the thermometer current branch is used for increasing the voltage of the RAMP signal by a voltage amplitude to generate a voltage offset; the RAMP current source branch comprises an invalid current branch and an effective circuit branch which are connected in parallel;
the invalid current branch circuit comprises a first PMOS current source group consisting of two first PMOS switches arranged in series and a second PMOS switch group consisting of two second PMOS switches arranged in parallel, the source electrode of the first PMOS current source group is grounded, the grid electrode of the first PMOS current source group is connected with the gain control module, the drain electrode of the first PMOS current source group is connected with the source electrode of the second PMOS switch group, the grid electrode of the second PMOS switch group is connected with the counter, and the drain electrodes of the two second PMOS switches are respectively connected with an invalid resistor and an effective resistor;
the effective current branch circuit comprises a third PMOS current source group consisting of two third PMOS switches arranged in series and a fourth PMOS switch group consisting of two fourth PMOS switches arranged in parallel, the source electrode of the third PMOS current source group is grounded, the grid electrode of the third PMOS current source group is connected with the gain control module, the drain electrode of the third PMOS current source group is connected with the source electrode of the fourth PMOS switch group, the grid electrode of the fourth PMOS switch group is connected with the counter, and the drain electrodes of the two fourth PMOS switches are respectively connected with the invalid resistor and the effective resistor;
the thermometer current branch comprises an NMOS switch, the thermometer current flows in through the drain electrode of the NMOS switch, the grid electrode of the NMOS switch is connected with a first timing control signal, and the source electrode of the NMOS switch is connected with an effective resistor.
As an optimization, the algorithm module calculates the thermometer current by the CDS value by using the following formula 1 and formula 2:
Voffset＝Iptat×RES2 (2)；
where Voffset represents the voltage offset and Iptat represents the thermometer current.
Preferably, the pixel signals comprise effective pixel signals and thermometer row pixel signals, the effective pixel signals are output through an effective row pixel area, the thermometer row pixel signals are output through a thermometer row pixel area, the effective row pixel area is composed of M rows and N columns of effective row pixel units, and the thermometer row pixel area is composed of 1 row and N columns of thermometer row pixel units.
As optimization, the output voltage of pixel signals of the thermometer row is a fixed value and cannot be changed due to the intensity of light; the output voltage of the effective pixel signal is variable and can be changed due to the intensity of the light.
As optimization, the pixel unit of the effective row comprises a first light-emitting diode, a first capacitor and a first to a fourth transmission gates,
the first end of the first light emitting diode and the first end of the first capacitor are respectively arranged on the drain electrode and the source electrode of the first transmission gate, and the second end of the first light emitting diode and the second end of the first capacitor are grounded;
the grid electrode of the first transmission gate is connected with a second time sequence control signal, the grid electrode of the second transmission gate is connected with a reset signal, the third transmission gate and the fourth transmission gate are arranged in series, and the grid electrode of the third transmission gate is connected with the first end of the first capacitor;
the drains of the third transmission gate and the second transmission gate are both connected with a positive power supply;
the source electrode of the second transmission gate is connected with the grid electrode of the third transmission gate;
the source electrode of the fourth transmission gate outputs an effective row pixel signal, and the grid electrode of the fourth transmission gate is connected with a pixel row selection signal;
the thermometer row pixel unit comprises a second light emitting diode, a second capacitor and fifth to eighth transmission gates,
the first end of the second light emitting diode and the first end of the second capacitor are respectively arranged at the drain electrode and the source electrode of the fifth transmission gate, and the second end of the second light emitting diode and the second end of the second capacitor are grounded;
the gates of the fifth transmission gate and the sixth transmission gate are both connected with a positive power supply VDDH, the seventh transmission gate and the eighth transmission gate are arranged in series, and the gate of the seventh transmission gate is connected with the first end of the second capacitor;
the drains of the sixth transmission gate and the seventh transmission gate are both connected with a positive power supply VDDH;
the source electrode of the sixth transmission gate is connected with the grid electrode of the seventh transmission gate;
the source electrode of the eighth transmission gate outputs a thermometer row pixel signal, and the gate electrode of the eighth transmission gate is connected with a pixel row selection signal.
The invention also discloses a method for the system for measuring the temperature of the image sensor, which comprises the following steps:
s1, measuring the voltage value of the original ramp signal and the voltage value of the pixel signal when the thermometer current Iptat does not enter the digital-to-analog converter;
s2, measuring the voltage value of a ramp signal and the voltage value of a pixel signal generated after the thermometer current Iptat enters the digital-to-analog converter;
s3, comparing the voltage values between the steps S1 and S2 to obtain a CDS value;
and S4, calculating the CDS value to obtain a value of the thermometer current, thereby obtaining a temperature value of the sensor.
As an optimization, the pixel signals comprise effective pixel signals and thermometer row pixel signals, the operating period of the thermometer row pixel signals is a thermometer row period, the operating period of the effective pixel signals is an effective row period, one thermometer row period is provided, a plurality of effective row periods are provided, and the thermometer current enters the digital-to-analog converter during the thermometer row period.
Preferably, in step S2, the thermometer current enters the dac during the Signal phase of the thermometer row cycle to raise the voltage of the ramp Signal by a voltage amplitude to generate the voltage offset Voffset.
As an optimization, the specific implementation steps of step S3 are as follows:
s3.1, in the Reset stage of the thermometer row period, comparing the ramp signal with the pixel signal by the comparator, and when the ramp signal is equal to the pixel signal, turning the level of the comparator downwards;
s3.2, the counter counts down when the ramp signal starts, and stops counting at the falling edge of the comparator, the time from the generation start of the ramp to the overturning of the comparator in the Reset stage is t1, and the counting result of the counter is a first counting value after t1 time;
s3.3, when the row period of the thermometer reaches a Signal stage, the thermometer current is connected into the digital-to-analog converter and triggers the digital-to-analog converter to send a new ramp Signal with the raised voltage amplitude, the time from the generation of the new ramp Signal to the overturning of the comparator in the Signal stage is t2, and the counting result of the counter is a second counting value after t2 time;
s3.4, calculating a CDS value: CDS | -the second count value | - | the first count value |.
Compared with the prior art, the invention has the following advantages and beneficial effects:
according to the invention, the structure of the DAC of the existing digital-to-analog converter is improved, the thermometer current branch is introduced, the measurement of the temperature inside the image sensor is realized, a temperature detection module is not separately designed, and the area of a chip is solved while the temperature of the sensor is accurately measured; meanwhile, time-sharing multiplexing of the comparator ADC is realized.
Drawings
In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and that for those skilled in the art, other related drawings can be obtained from these drawings without inventive effort. In the drawings:
FIG. 1 is a schematic diagram of the structure of an image sensor temperature measurement system of the present invention;
FIG. 2 is a diagram of the internal circuit structure of the digital-to-analog converter of the present invention;
FIG. 3 is a flow chart illustrating the functional operation of the thermometer during the trip;
FIG. 4 is a schematic diagram of a pixel cell distribution of an image sensor according to the present invention;
FIG. 5 is a frame timing diagram of the temperature measurement method of the present invention;
fig. 6 is a functional operation flow diagram of the temperature measuring method of the image sensor according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Example 1
A system for image sensor temperature comprises a digital-to-analog converter 1, a comparator 2 and an algorithm module 3 which are carried in the system;
the digital-to-analog converter 1 is used for generating a ramp signal, a thermometer current Iptat is input to an input end of the digital-to-analog converter 1, and the voltage of the ramp signal is raised by a voltage amplitude through the thermometer current Iptat to generate a voltage offset Voffset;
the comparator 2 is used for comparing the ramp signal output by the digital-to-analog converter 1 with the pixel signal, when the values of the ramp signal and the pixel signal are equal, the level of the comparator 2 is inverted downwards, and when a new ramp signal is generated, the level of the comparator 2 is inverted upwards;
a counter 4 is arranged in the digital-to-analog converter, and the counter 4 is used for starting counting when a ramp signal is generated and stopping counting when the comparator 2 generates a falling edge; when the thermometer current Iptat flows into the digital-to-analog converter 1 to generate a new ramp signal and raise the ramp signal by a voltage amplitude, the counter starts counting again, when the new ramp signal is equal to the pixel signal value again, the counter stops counting, and the output value of the counter for the second time subtracts the output value of the counter for the first time to obtain the CDS value;
the algorithm module 3 calculates the CDS value to obtain the thermometer current Iptat input to the input terminal of the digital-to-analog converter 1, thereby obtaining the sensor temperature.
In this embodiment, the algorithm module 4 calculates the thermometer current Iptat by using the CDS value according to the following formula 1 and formula 2:
Voffset＝Iptat×RES2 (2)。
the invention discloses a DAC (digital-to-analog converter) of a current steering type for generating a Ramp signal, which has the principle that current changing along with a digital input signal flows through a terminal resistor to generate voltage drop, so that the Ramp signal is generated and is input into a comparator.
The invention causes the temperature meter current (IPTAT) to flow through the terminal resistor of the DAC, and then the ramp signal is raised by a voltage amplitude. This amount of lift-off will eventually be reflected in the CDS output value of the counter. Specifically, the larger the lift-off voltage amplitude, the larger the CDS value of the counter. The ADC range and the ADC full-scale count value are parameters set by the comparator in factory, and the method is the prior art.
For example:
assuming that the ADC range is 1V, Voffset value is 0.5V, and ADC full-scale count value is 4095, then the CDS value is 2047 at this time. And then, the sensor temperature corresponding to the current of the thermometer at the moment can be calculated according to the linear relation between the CDS value and the sensor temperature. The Column ADC (comparator) works as follows:
a. a comparator (ADC) with an Auto Zero (Auto Zero) function compares the RAMP signal and the Pixel Ouput (Pixel voltage output signal). Both Ramp (Ramp) and Pixel Signal (Pixel Signal) described in fig. 2 are signals after zero calibration, i.e. the two signals have the same potential at the beginning of a line period within a time interval.
b. The counter starts counting at the beginning of the RAMP, and is divided into a SIGNAL phase and a RESET phase two-time counting process. The RESET phase counts down (0 → negative) and is referred to as a first count value, and the SIGNAL phase counts up (negative → 0 or negative → 0 → positive) and is referred to as a second count value.
c. The final count result is | the second count value | - | the first count value |.
In this embodiment, the digital-to-analog converter further includes a RAMP current source branch, a thermometer current branch, and a gain control module, where the RAMP current source branch is configured to generate a current with a step change, the current generates a RAMP signal with a step change after flowing through an effective resistor RES2, and the thermometer current branch is configured to raise a voltage of the RAMP signal by a voltage amplitude to generate a voltage offset Voffset; the RAMP current source branch comprises an invalid current branch and an effective circuit branch which are connected in parallel;
the invalid current branch circuit comprises a first PMOS current source group consisting of two first PMOS switches arranged in series and a second PMOS switch group consisting of two second PMOS switches arranged in parallel, the source electrode of the first PMOS current source group is connected with a power supply, the grid electrode of the first PMOS current source group is connected with the gain control module, the drain electrode of the first PMOS current source group is connected with the source electrode of the second PMOS switch group, the grid electrode of the second PMOS switch group is connected with the counter, and the drain electrodes of the two second PMOS switches are respectively connected with an invalid resistor RES1 and an effective resistor RES 2;
the effective current branch circuit comprises a third PMOS current source group consisting of two third PMOS switches arranged in series and a fourth PMOS switch group consisting of two fourth PMOS switches arranged in parallel, the source electrode of the third PMOS current source group is connected with a power supply, the grid electrode of the third PMOS current source group is connected with the gain control module, the drain electrode of the third PMOS current source group is connected with the source electrode of the fourth PMOS switch group, the grid electrode of the fourth PMOS switch group is connected with the counter, and the drain electrodes of the two fourth PMOS switches are respectively connected with an ineffective resistor RES1 and an effective resistor RES 2;
the thermometer current branch comprises an NMOS switch MNO, the thermometer current flows in through the drain electrode of the NMOS switch, the grid electrode of the NMOS switch is connected with a first timing control signal EN _ IPTAT, and the source electrode of the NMOS switch is connected with an effective resistor RES 2.
In fig. 2, the branch of the RAMP current source (PMOS type) mainly generates a current with a step change, and the current generates a RAMP signal with a step change after flowing through the termination resistor RES 2. Certainly, a plurality of PMOS current source groups having the same structure as the first PMOS current source group may be connected in parallel between the first PMOS current source group and the third PMOS current source group; a plurality of PMOS switch groups with the same structure as the second PMOS switch group can be arranged between the second PMOS switch group and the fourth PMOS switch group in parallel, and the number of the PMOS switch groups corresponds to the number of the PMOS current source groups one to one and corresponds to the number of the resistors.
The thermometer current branch input is thermometer current (IPTAT), and is connected into a terminal resistor RES2 after passing through an NMOS switch (MN0), wherein the gate of MN0 is connected with a timing control signal EN _ IPTAT. When the EN _ IPTAT is at a high level, the switch is conducted; when EN _ IPTAT is low level, the switch is turned off.
The functional operation flow of the thermometer in the invention is shown in fig. 3.
EN _ IPTAT: the IPTAT current path switch enable signal.
Ramp: a ramp signal. During the period when EN _ IPTAT is high, the ramp signal as a whole is raised by a voltage magnitude Voffset, which is proportional to the IPTAT current.
Pixel Signal: the Pixel signal is a fixed voltage value when the thermometer is in a line period.
The output of the comparator is as follows: when the Ramp Signal Ramp is intersected with the Pixel Signal Pixel, the comparator is turned downwards;
the counter outputs: the counter value starts counting when a Ramp is generated, stops counting when the comparator is turned over, counts from zero to the negative direction in the first Ramp phase (SIGNAL phase), counts from the negative to the positive direction in the second Ramp phase (RESET phase), and increases the count value as the IPTAT current increases and the intersection point of Ramp and Pixel SIGNAL becomes closer to the rear.
The pixel unit distribution of the image sensor of the invention is shown in fig. 4:
the pixel module of the image sensor with the temperature measuring system consists of an effective row pixel area and a thermometer row pixel area. The effective row pixel area consists of M rows and N columns of effective row pixel units and is used for outputting effective pixel signals; the thermometer row pixel area is composed of 1 row and N columns of thermometer row pixel units and used for outputting thermometer row pixel signals.
In this embodiment, the output voltage of the pixel signal of the thermometer row is a fixed value and does not change due to the intensity of the light; the output voltage of the effective pixel signal is variable and can be changed due to the intensity of the light.
The active row pixel unit comprises a first light emitting diode D1, a first capacitor C1 and first to fourth transmission gates Q1-Q4,
a first end of the first light emitting diode D1 and a first end of a first capacitor C1 are respectively arranged at the drain and the source of the first transmission gate Q1, and a second end of the first light emitting diode D1 and a second end of the first capacitor C1 are grounded;
the Gate of the first transmission Gate Q1 is connected to a second timing control signal transfer Gate, the Gate of the second transmission Gate is connected to a reset signal reset, the third transmission Gate Q3 and the fourth transmission Gate Q4 are arranged in series, and the Gate of the third transmission Gate Q3 is connected to the first end of the first capacitor C1;
the drains of the third transmission gate Q3 and the second transmission gate Q2 are both connected with a positive power supply VDDH;
the source of the second transmission gate Q2 is connected with the gate of a third transmission gate Q3;
the source of the fourth transmission gate Q4 outputs an active row pixel signal, and the gate of the fourth transmission gate Q4 is connected to a pixel row selection signal select;
the pixel unit of the thermometer row comprises a second light emitting diode D2, a second capacitor C2 and fifth to eighth transmission gates Q5-Q8,
a first end of the second light emitting diode D2 and a first end of a second capacitor C2 are respectively disposed at the drain and the source of the fifth transmission gate Q5, and a second end of the second light emitting diode D2 and a second end of the second capacitor C2 are grounded;
the gates of the fifth transmission gate Q5 and the sixth transmission gate Q6 are both connected to a positive power supply VDDH, the seventh transmission gate Q7 and the eighth transmission gate Q8 are arranged in series, and the gate of the seventh transmission gate Q7 is connected to a first end of a second capacitor C2;
the drains of the sixth transmission gate Q6 and the seventh transmission gate Q7 are both connected with a positive power supply VDDH;
the source of the sixth transmission gate Q6 is connected with the gate of a seventh transmission gate Q7;
the source of the eighth transfer gate Q8 outputs a thermometer row pixel signal, and the gate of the eighth transfer gate Q8 is connected to a pixel row selection signal select.
The difference between the thermometer row pixels and the active row pixels is that the control signals of the respective pixel tubes are not consistent, that is: the pixel tubes Q1, Q2 of the active row are time-controlled, while the pixel tubes Q1, Q2 of the thermometer row are directly fixed (i.e., connected to the power supply).
The effective pixel region is composed of M-N effective row pixel units and outputs effective pixel signals.
The thermometer row area is composed of 1 × N thermometer row Pixel cells, and outputs Pixel signals of thermometer rows.
A thermometer row: the Transfer Gate and Reset signals of the pixel are connected to the positive power supply (VDDH), so the fd (floating diffusion) point potential is a constant value close to the VDDH power supply voltage.
Effective row: the Transfer Gate and Reset signals of the pixel are controlled by timing. Generally, the FD point potential varies within one row period.
In particular, the Select signal is a row Select signal of the pixel. When the Select Signal is high, the current Pixel row is selected, so that the Pixel Signal is accessed to the comparator. A typical frame timing is to select rows of pixels from bottom to top row by row.
FIG. 5 is a frame timing diagram of the temperature measurement method of the present invention. The thermometer measurement will take one line period after VBlank and before the active pixels. Therefore, the frequency of temperature data acquisition is 1 time per frame. Under the condition that the requirement on the precision of the thermometer is high, the temperature can be measured through a plurality of line periods so as to reduce the influence of line noise on the measured value, and the time division multiplexing of the comparator ADC is realized. VBlank is a vertical blank, and since the sensor needs to finish reading all pixel rows of the pixels in the pixel module within a frame time, but the sensor often finishes reading all pixel rows without a frame time, the time left by removing the time for reading the pixel rows by the sensor in a frame time is a vertical blank, that is, an idle time for vertical scanning of the pixels.
Example 2:
the invention also discloses a method for measuring the temperature of the image sensor, which comprises the following steps:
s1, measuring the voltage value of the original ramp signal and the voltage value of the pixel signal when the thermometer current Iptat does not enter the digital-to-analog converter;
s2, measuring the voltage value of a ramp signal and the voltage value of a pixel signal generated after the thermometer current Iptat enters the digital-to-analog converter;
s3, comparing the voltage values between steps S1 and S2 to obtain CDS value, so that the influence of random noise on the measured value can be reduced.
And S4, calculating the CDS value to obtain a value of the thermometer current, thereby obtaining a temperature value of the sensor.
In this embodiment, the operation period of the pixel signal of the thermometer row is a thermometer row period, the operation period of the effective pixel signal is an effective row period, there is one thermometer row period, there are a plurality of effective row periods, and the thermometer current enters the digital-to-analog converter during the thermometer row period.
In this embodiment, in step S2, the thermometer current enters the dac at the Signal stage of the thermometer row period to raise the voltage of the ramp Signal by a voltage amplitude to generate the voltage offset Voffset.
In this embodiment, the specific implementation steps of step S3 are as follows:
s3.1, in the Reset stage of the thermometer row period, comparing the ramp signal with the pixel signal by the comparator, and when the ramp signal is equal to the pixel signal, turning the level of the comparator downwards;
s3.2, the counter counts down when the ramp signal starts, and stops counting at the falling edge of the comparator, the time from the generation start of the ramp to the overturning of the comparator in the Reset stage is t1, and the counting result of the counter is a first counting value after t1 time;
s3.3, when the row period of the thermometer reaches a Signal stage, the thermometer current is connected into the digital-to-analog converter and triggers the digital-to-analog converter to send a new ramp Signal with the raised voltage amplitude, the time from the generation of the new ramp Signal to the overturning of the comparator in the Signal stage is t2, and the counting result of the counter is a second counting value after t2 time;
s3.4, calculating a CDS value: CDS | -the second count value | - | the first count value |.
The invention discloses a functional action flow diagram of a temperature measuring method of an image sensor. The state flag is the state of the current line period, and comprises 3 states of Vblank (vertical blank), thermometer and effective pixel. The SEL signal is a row selection signal for the pixels, each row of pixels individually corresponding to one SEL signal. If the thermometer row corresponds to SEL <0>, when SEL <0> is high level, the thermometer row is selected, then the Pixel Signal Signal of the thermometer row is connected to the Column ADC. The active pixels are typically selected row by row, with SEL <1> SEL < M > being a Rolling action as shown in FIG. 6. EN _ IPTAT is an enable Signal for thermometer current to the DAC, it can be seen that thermometer current is only enabled to flow into the DAC if and only if it is in the Signal phase of the thermometer row period, whereas the usual active pixel row period EN _ IPTAT is always low (not enabled).
RAMP is a RAMP Signal generated by the DAC module, and if and only if the Signal phase of the thermometer row period will raise a voltage offset (Voffset) with the thermometer current flowing, the Voffset will not appear in the effective pixel row period.
Expressions (such as "first", "second", and the like) used in various embodiments of the present invention may modify various constituent elements in various embodiments, but may not limit the respective constituent elements. For example, the above description does not limit the order and/or importance of the elements described. The foregoing description is for the purpose of distinguishing one element from another. For example, the first user device and the second user device indicate different user devices, although both are user devices. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of various embodiments of the present invention.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. The image sensor temperature measuring system is characterized by comprising a digital-to-analog converter, a comparator and an algorithm module which are carried in the image sensor temperature measuring system;
the digital-to-analog converter is used for generating a ramp signal, thermometer current is input to the input end of the digital-to-analog converter, and the thermometer current raises the voltage of the ramp signal by one voltage amplitude after passing through the digital-to-analog converter to generate voltage offset;
the comparator is used for comparing the ramp signal output by the digital-to-analog converter with the pixel signal, when the value of the ramp signal is equal to that of the pixel signal, the level of the comparator is inverted downwards, and when a new ramp signal is generated, the level of the comparator is inverted upwards;
the digital-to-analog converter is also internally provided with a counter, and the counter is used for starting counting when a ramp signal is generated and stopping counting when the comparator generates a falling edge; when the thermometer current Iptat flows into the digital-to-analog converter to generate a new ramp signal and the ramp signal is raised by a voltage amplitude, the counter starts counting again, when the new ramp signal is equal to the pixel signal value again, the counter stops counting, and the output value of the counter for the second time subtracts the output value of the counter for the first time to obtain a CDS value;
and the algorithm module calculates the CDS value to obtain a thermometer current value input to the input end of the digital-to-analog converter, so that the temperature of the sensor is obtained.
2. The image sensor temperature measuring system of claim 1, wherein the digital-to-analog converter further comprises a RAMP current source branch, a thermometer current branch and a gain control module, the RAMP current source branch is configured to generate a step-change current, the step-change current generates a step-change RAMP signal after flowing through an effective resistor RES2, and the thermometer current branch is configured to raise a voltage of the RAMP signal by a voltage amplitude to generate a voltage offset; the RAMP current source branch comprises an invalid current branch and an effective circuit branch which are connected in parallel;
the invalid current branch circuit comprises a first PMOS current source group consisting of two first PMOS switches arranged in series and a second PMOS switch group consisting of two second PMOS switches arranged in parallel, the source electrode of the first PMOS current source group is connected with a power supply, the grid electrode of the first PMOS current source group is connected with the gain control module, the drain electrode of the first PMOS current source group is connected with the source electrode of the second PMOS switch group, the grid electrode of the second PMOS switch group is connected with the counter, and the drain electrodes of the two second PMOS switches are respectively connected with an invalid resistor RES1 and an effective resistor RES 2;
the effective current branch circuit comprises a third PMOS current source group consisting of two third PMOS switches arranged in series and a fourth PMOS switch group consisting of two fourth PMOS switches arranged in parallel, the source electrode of the third PMOS current source group is connected with a power supply, the grid electrode of the third PMOS current source group is connected with the gain control module, the drain electrode of the third PMOS current source group is connected with the source electrode of the fourth PMOS switch group, the grid electrode of the fourth PMOS switch group is connected with the counter, and the drain electrodes of the two fourth PMOS switches are respectively connected with an ineffective resistor RES1 and an effective resistor RES 2;
the thermometer current branch comprises an NMOS switch MNO, the thermometer current flows in through the drain electrode of the NMOS switch, the grid electrode of the NMOS switch is connected with a first timing control signal EN _ IPTAT, and the source electrode of the NMOS switch is connected with an effective resistor RES 2.
3. The image sensor temperature measurement system of claim 2, wherein the algorithm module calculates the thermometer current from the CDS value by using equations 1 and 2:
Voffset＝Iptat×RES2 (2)；
where Voffset represents the voltage offset and Iptat represents the thermometer current.
4. The image sensor temperature measurement system according to claim 1, wherein the pixel signals include effective pixel signals and thermometer row pixel signals, the effective pixel signals are output through an effective row pixel area, the thermometer row pixel signals are output through a thermometer row pixel area, the effective row pixel area is composed of M rows and N columns of effective row pixel units, and the thermometer row pixel area is composed of 1 row and N columns of thermometer row pixel units.
5. The image sensor temperature measurement system of claim 4, wherein the output voltage of the thermometer row pixel signal is constant and does not vary due to the intensity of the light; the output voltage of the effective pixel signal is variable and can be changed due to the intensity of the light.
6. The image sensor temperature measurement system according to claim 4 or 5, wherein the active row pixel unit includes a first light emitting diode (D1), a first capacitor (C1), and first to fourth transfer gates (Q1-Q4),
a first end of the first light emitting diode (D1) and a first end of a first capacitor (C1) are respectively arranged at the drain electrode and the source electrode of the first transmission gate (Q1), and a second end of the first light emitting diode (D1) and a second end of the first capacitor (C1) are grounded;
the Gate of the first transmission Gate (Q1) is connected with a second timing control signal (transfer Gate), the Gate of the second transmission Gate is connected with a reset signal (reset), the third transmission Gate (Q3) and the fourth transmission Gate (Q4) are arranged in series, and the Gate of the third transmission Gate (Q3) is connected with the first end of the first capacitor (C1);
the drains of the third transmission gate (Q3) and the second transmission gate (Q2) are both connected to a positive power supply (VDDH);
the source of the second transmission gate (Q2) is connected with the gate of a third transmission gate (Q3);
the source of the fourth transfer gate (Q4) outputs an active row pixel signal, and the gate of the fourth transfer gate (Q4) is connected to a pixel row select signal (select);
the thermometer row pixel unit comprises a second light emitting diode (D2), a second capacitor (C2) and fifth to eighth transmission gates (Q5-Q8),
a first end of the second light emitting diode (D2) and a first end of a second capacitor (C2) are respectively arranged at the drain electrode and the source electrode of the fifth transmission gate (Q5), and a second end of the second light emitting diode (D2) and a second end of the second capacitor (C2) are grounded;
the gates of the fifth transmission gate (Q5) and the sixth transmission gate (Q6) are both connected with a positive power supply (VDDH), the seventh transmission gate (Q7) and the eighth transmission gate (Q8) are arranged in series, and the gate of the seventh transmission gate (Q7) is connected with the first end of a second capacitor (C2);
the drains of the sixth transmission gate (Q6) and the seventh transmission gate (Q7) are both connected to a positive power supply VDDH;
the source of the sixth transmission gate (Q6) is connected with the gate of a seventh transmission gate (Q7);
the source of the eighth transfer gate (Q8) outputs a thermometer row pixel signal, and the gate of the eighth transfer gate (Q8) is connected to a pixel row select signal (select).
7. A temperature measuring method of an image sensor based on the image sensor temperature measuring system according to any one of claims 1 to 6, comprising the steps of:
s1, measuring the voltage value of the original ramp signal and the voltage value of the pixel signal when the thermometer current does not enter the digital-to-analog converter;
s2, measuring the voltage value of a ramp signal and the voltage value of a pixel signal generated after the thermometer current enters the digital-to-analog converter;
s3, comparing the voltage values between the steps S1 and S2 to obtain a CDS value;
and S4, calculating the CDS value to obtain a value of the thermometer current, thereby obtaining a temperature value of the sensor.
8. The method of claim 7, wherein the pixel signals comprise active pixel signals and thermometer row pixel signals, the operating period of the thermometer row pixel signals is a thermometer row period, the operating period of the active pixel signals is an active row period, the number of the thermometer row periods is one, the number of the active row periods is plural, and the thermometer current enters the digital-to-analog converter during the thermometer row period.
9. The method as claimed in claim 8, wherein in step S2, a thermometer current enters the dac during Signal phase of the thermometer row period to generate a voltage offset for increasing a voltage amplitude of the ramp Signal voltage.
10. The method for measuring the temperature of the image sensor according to claim 9, wherein the step S3 is implemented as follows:
s3.1, in the Reset stage of the thermometer row period, comparing the ramp signal with the pixel signal by the comparator, and when the ramp signal is equal to the pixel signal, turning the level of the comparator downwards;
s3.2, the counter counts down when the ramp signal starts, and stops counting at the falling edge of the comparator, the time from the generation start of the ramp to the overturning of the comparator in the Reset stage is t1, and the counting result of the counter is a first counting value after t1 time;
s3.3, when the row period of the thermometer reaches a Signal stage, the thermometer current is connected into the digital-to-analog converter and triggers the digital-to-analog converter to send a new ramp Signal with the raised voltage amplitude, the time from the generation of the new ramp Signal to the overturning of the comparator in the Signal stage is t2, and the counting result of the counter is a second counting value after t2 time;
s3.4, calculating a CDS value: CDS | -the second count value | - | the first count value |.
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