Analog-to-digital conversion method applied to column-level analog-to-digital converter

Abstract

The invention relates to an analog-to-digital conversion method applied to a column-level analog-to-digital converter. The analog-to-digital conversion method comprises the following steps: 1) signal acquisition; 2) sample holding; 3) analog-to-digital conversion; 4) column-level parallel processing; 5) digital output; and 6) data integration. According to the analog-to-digital conversion method applied to the column-level analog-to-digital converter, the dynamic range of a traditional column-level analog-to-digital converter is enlarged, meanwhile, the range of scene illumination detected by a sensor of the column-level analog-to-digital converter is enlarged, details of an image are increased, and finally the quality of the obtained image is improved; the input offset voltage influence and the large noise influence of a comparator are reduced, and the problems that the dynamic range of a conventional monoclinic column-level ADC is small, so that the range of scene illumination detected by a sensor using the column-level ADC is narrow, image details are few, the quality of a finally obtained image is poor, the comparator is a key part in the ADC, and the image quality is poor are solved. However, the problems of the influence of input offset voltage of the comparator and the influence of relatively large noise exist.

Description

Technical Field

[0001] The present invention relates to the technical field of column-level analog-to-digital converters, and in particular to an analog-to-digital conversion method applied to a column-level analog-to-digital converter. Background Art

[0002] A digital-to-analog converter, also known as a D / A converter, or DAC for short, is a device that converts digital quantities into analog quantities. A D / A converter is basically composed of four parts, namely a weighted resistor network, an operational amplifier, a reference power supply, and an analog switch. A digital-to-analog converter is generally used in an analog-to-digital converter. An analog-to-digital converter is an A / D converter, or ADC for short. It is a device that converts continuous analog signals into discrete digital signals. A column-level analog-to-digital converter is an analog-to-digital converter architecture, typically used for high-speed, high-precision analog-to-digital signal conversion. This type of ADC uses multiple sub-ADCs and parallel processing to improve conversion speed and accuracy.

[0003] In the prior art, during the use of column-level analog-to-digital converters, the column-level analog-to-digital converter is a key technology for applications such as digital image sensors, which allows high-speed and high-efficiency conversion of analog signals to digital signals. Among the existing column-level ADCs, commonly used structures include successive approximation ADC, cyclic ADC and single slope ADC, among which the successive approximation ADC and the cyclic ADC occupy a larger area, but the conversion speed is faster. On the contrary, the single slope ADC has a simple structure, but the conversion speed is exponentially related to the number of conversion bits, and the conversion time is relatively long. The dynamic range of the conventional single slope column-level ADC is small, so that the sensor using the column-level ADC can detect a narrow range of scene illumination and few image details, and the final image quality is poor. The comparator is a key part of the ADC, but there will be an input offset voltage influence of the comparator, and there will be a large noise influence. Therefore, an analog-to-digital conversion method applied to the column-level analog-to-digital converter is proposed to solve the above problems. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides an analog-to-digital conversion method applied to a column-level analog-to-digital converter, which has the advantage of high image quality and solves the problem that the conventional single-slope column-level ADC has a small dynamic range, so that the sensor using the column-level ADC can detect a narrow range of scene illumination and few image details, and the final image quality is poor. The comparator is a key part of the ADC, but there will be the influence of the input offset voltage of the comparator and the problem of greater noise.

[0005] To achieve the above object, the present invention provides the following technical solution: an analog-to-digital conversion method applied to a column-level analog-to-digital converter, comprising the following steps:

[0006] 1) Signal acquisition;

[0007] 2) Sample retention;

[0008] 3) Analog-to-digital conversion;

[0009] 4) Column-level parallel processing;

[0010] 5) Digital output;

[0011] 6) Data integration.

[0012] Furthermore, the signal acquisition in step 1) needs to acquire analog signals through a series of light sensors or pixel arrays. These signals are usually light intensity values ​​from light sensors, and each pixel represents a part of the image.

[0013] Furthermore, the analog signal collected in step 1) must go through a sample hold stage to retain its value before analog-to-digital conversion, and the sample hold circuit in step 2) holds the value of the analog signal in a capacitor or register to wait for conversion.

[0014] Further, the analog-to-digital conversion in step 3) includes the following sub-steps:

[0015] S1 uses one or more comparators to compare the analog signal held by the sample with a reference voltage. The result of the comparison is a bit stream indicating whether the signal is greater than or less than the reference voltage.

[0016] The output of S2 comparator will pass through the encoder to convert the bit stream into a digital code, which is in binary form.

[0017] Furthermore, different columns in step 4) can be independently converted into analog-to-digital signals, and the entire array can process multiple signals simultaneously. After each column is converted into analog-to-digital signals in step 5), the digital output is transmitted to a digital signal processor (DSP), and various subsequent processing such as image processing, encoding and compression can be performed at the digital signal processor (DSP).

[0018] Furthermore, the signal acquisition in the step 1) requires a prefilter, which can also be replaced by an anti-aliasing filter, whose function is to filter out high-frequency components in the input analog signal. The prefilter filters the input signal and outputs an analog signal. The analog signal is sampled into a capacitor by a sample-and-hold circuit and held. According to the Nyquist sampling theorem, the sampling frequency of the sample-and-hold circuit must be greater than twice the signal frequency. If this condition is not met, aliasing will occur in the spectrum after sampling, causing the signal to change. The sample-and-hold circuit outputs a time-discrete analog signal after sampling, which is input to a quantizer for quantization. The quantizer has a certain quantization range, which can be divided into several sub-areas with equal amplitudes, and the number of intervals is determined by the quantization resolution.

[0019] Furthermore, the resolution is used to measure the ability of the analog-to-digital converter to distinguish the minimum analog input amplitude, that is, the analog voltage amplitude corresponding to the input when the digital code output by the analog-to-digital converter changes by 1 bit, usually expressed in the least significant bit LSB. The resolution represents the minimum analog input that the ADC can quantize. For an n-bit analog-to-digital converter with a full-scale voltage of V, the formula for the minimum analog voltage change that can be distinguished is:

[0020] Where LSB is the least significant bit and V is the full-scale voltage of the analog-to-digital converter.

[0021] Furthermore, the comparator compares two analog input signals when working and outputs a high level or a low level signal. The comparator can be composed of an open-loop operational amplifier. Ideally, when the difference between the signals at the in-phase input and the inverting input of the comparator is positive, the comparator outputs a high level, and when the difference between the signals is negative, the comparator outputs a low level.

[0022] Furthermore, when the comparator needs to output a high level, the counter is used to complete the quantization of 1LSB, and the quantization speed of the counter depends on the frequency of the main clock.

[0023] Furthermore, the final digital output data in step 6) can be transmitted to a microcontroller, FPGA, or other digital system via a digital bus for further processing and analysis.

[0024] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0025] The analog-to-digital conversion method applied to the column-level analog-to-digital converter increases the dynamic range of the traditional column-level analog-to-digital converter, and at the same time improves the range of scene illumination detected by the sensor of the column-level analog-to-digital converter, increases the details of the image, and finally improves the quality of the obtained image, reduces the influence of the input offset voltage of the comparator and the influence of large noise, and solves the problem that the dynamic range of the conventional single-slope column-level ADC is small, so that the sensor using the column-level ADC can detect a narrow range of scene illumination, few image details, and finally obtain poor image quality. The comparator is a key part of the ADC, but there will be problems such as the influence of the input offset voltage of the comparator and the influence of large noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a flowchart of the conversion method in the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] See also Figure 1 In this embodiment, an analog-to-digital conversion method applied to a column-level analog-to-digital converter includes the following steps:

[0029] 1) Signal acquisition. In this step, the analog signal is discretely sampled in time to obtain a series of analog values. The sampling frequency is usually determined by the sampling theorem (or Nyquist theorem), ensuring that the sampling frequency is at least twice the signal frequency to avoid aliasing distortion;

[0030] 2) Sample retention;

[0031] 3) Analog-to-digital conversion;

[0032] 4) Column-level parallel processing. After sampling, each analog value is mapped to a discrete digital value. This process is called quantization. The quantization process is based on the resolution of the ADC, mapping the continuous range of analog signals to a limited set of discrete values. The higher the resolution, the higher the accuracy with which the ADC can represent the signal.

[0033] 5) Digital output;

[0034] 6) Data integration: The output data of multiple sub-ADCs are combined and processed to produce the final digital output. This may include weighted addition of the outputs of the sub-ADCs to improve the overall resolution. The digital processing unit may also perform other calibration and error correction operations to ensure accurate results.

[0035] The signal acquisition in step 1) requires collecting analog signals through a series of light sensors or pixel arrays. These signals are usually light intensity values ​​from light sensors, and each pixel represents a part of the image.

[0036] The analog signal collected in step 1) must pass through a sample hold stage to retain its value before analog-to-digital conversion. The sample hold circuit in step 2) holds the value of the analog signal in a capacitor or register to wait for conversion.

[0037] The analog-to-digital conversion in step 3) includes the following sub-steps:

[0038] S1 uses one or more comparators to compare the analog signal held by the sample with a reference voltage. The result of the comparison is a bit stream indicating whether the signal is greater than or less than the reference voltage.

[0039] The output of the S2 comparator will pass through the encoder to convert the bit stream into a digital code. The digital code is in binary form, or it can be two's complement, binary original, or other forms.

[0040] In step 4), different columns can be independently converted to digital, and the entire array can process multiple signals simultaneously. In step 5), after each column is converted to digital, the digital output is transmitted to the digital signal processor (DSP), and various subsequent processing such as image processing, encoding and compression can be performed at the digital signal processor (DSP).

[0041] The signal acquisition in step 1) requires a prefilter, which can also be replaced by an anti-aliasing filter, which is used to filter out high-frequency components in the input analog signal. The prefilter filters the input signal and outputs an analog signal. The analog signal is sampled into a capacitor by a sample-and-hold circuit and held. According to the Nyquist sampling theorem, the sampling frequency of the sample-and-hold circuit must be greater than twice the signal frequency. If this condition is not met, aliasing will occur in the spectrum after sampling, causing the signal to change. The sample-and-hold circuit outputs a time-discrete analog signal after sampling, which is input to a quantizer for quantization. The quantizer has a certain quantization range, which can be divided into several sub-areas with equal amplitudes, and the number of intervals is determined by the quantization resolution.

[0042] Resolution is used to measure the ability of an analog-to-digital converter to distinguish the minimum analog input amplitude, that is, the analog voltage amplitude corresponding to the input when the digital code output by the analog-to-digital converter changes by 1 bit. It is usually expressed in the least significant bit (LSB). Resolution represents the minimum analog input that the ADC can quantize. For an n-bit analog-to-digital converter with a full-scale voltage of V, the formula for the minimum analog voltage change that can be distinguished is:

[0043] Where LSB is the least significant bit and V is the full-scale voltage of the analog-to-digital converter.

[0044] When working, the comparator compares two analog input signals and outputs a high or low level signal. The comparator can be composed of an open-loop operational amplifier. Ideally, when the difference between the signals at the comparator's in-phase input and inverting input is positive, the comparator outputs a high level, and when the difference between the signals is negative, the comparator outputs a low level.

[0045] When the comparator needs to output a high level, the counter is used to complete the quantization of 1LSB, and the quantization speed of the counter depends on the frequency of the main clock.

[0046] The final digital output data in step 6) can be transmitted to a microcontroller, FPGA, or other digital system via a digital bus for further processing and analysis.

[0047] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0048] The analog-to-digital conversion method applied to the column-level analog-to-digital converter increases the dynamic range of the traditional column-level analog-to-digital converter, and at the same time improves the range of scene illumination detected by the sensor of the column-level analog-to-digital converter, increases the details of the image, and finally improves the quality of the obtained image, reduces the influence of the input offset voltage of the comparator and the influence of large noise, and solves the problem that the dynamic range of the conventional single-slope column-level ADC is small, so that the sensor using the column-level ADC can detect a narrow range of scene illumination, few image details, and finally obtain poor image quality. The comparator is a key part of the ADC, but there will be problems such as the influence of the input offset voltage of the comparator and the influence of large noise.

[0049] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0050] While the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that many changes, modifications, substitutions and variations can be made to the embodiments without departing from the principles and spirit of the invention.

Claims

1. An analog-to-digital conversion method applied to a column-level analog-to-digital converter, characterized in that: The following steps are involved: 1) Signal acquisition; 2) Sample retention; 3) Analog-to-digital conversion; 4) Column-level parallel processing; 5) Digital output; 6) Data integration.

2. The analog-to-digital conversion method applied to a column-level analog-to-digital converter according to claim 1, characterized in that: The signal acquisition in step 1) requires collecting analog signals through a series of light sensors or pixel arrays. These signals are usually light intensity values ​​from light sensors, and each pixel represents a part of the image.

3. The analog-to-digital conversion method applied to a column-level analog-to-digital converter according to claim 1, characterized in that: The analog signal collected in step 1) must go through a sample hold stage to retain its value before analog-to-digital conversion. The sample hold circuit in step 2) holds the value of the analog signal in a capacitor or register to wait for conversion.

4. The analog-to-digital conversion method applied to a column-level analog-to-digital converter according to claim 1, characterized in that: The analog-to-digital conversion in step 3) includes the following sub-steps: S1 uses one or more comparators to compare the analog signal held by the sample with a reference voltage. The result of the comparison is a bit stream indicating whether the signal is greater than or less than the reference voltage. The output of the S2 comparator will pass through the encoder to convert the bit stream into a digital code, which is encoded in binary form.

5. The analog-to-digital conversion method applied to a column-level analog-to-digital converter according to claim 4, characterized in that: In step 4), different columns can be independently converted into analog-to-digital signals, and the entire array can process multiple signals simultaneously. In step 5), after each column is converted into analog-to-digital signals, the digital output is transmitted to a digital signal processor (DSP), and various subsequent processing such as image processing, encoding and compression can be performed at the digital signal processor (DSP).

6. The analog-to-digital conversion method applied to a column-level analog-to-digital converter according to claim 1, characterized in that: The signal acquisition in the step 1) requires a prefilter, which can also be replaced by an anti-aliasing filter, whose function is to filter out high-frequency components in the input analog signal. The prefilter filters the input signal and outputs an analog signal. The analog signal is sampled into a capacitor by a sample-and-hold circuit and held. According to the Nyquist sampling theorem, the sampling frequency of the sample-and-hold circuit must be greater than twice the signal frequency. If this condition is not met, aliasing will occur in the spectrum after sampling, causing the signal to change. The sample-and-hold circuit outputs a time-discrete analog signal after sampling, which is input to a quantizer for quantization. The quantizer has a certain quantization range, which can be divided into several sub-areas with equal amplitudes, and the number of intervals is determined by the quantization resolution.

7. The analog-to-digital conversion method applied to a column-level analog-to-digital converter according to claim 6, characterized in that: The resolution is used to measure the ability of the analog-to-digital converter to distinguish the minimum analog input amplitude, that is, the analog voltage amplitude corresponding to the input when the digital code output by the analog-to-digital converter changes by 1 bit. It is usually expressed in the least significant bit (LSB). The resolution represents the minimum analog input that the ADC can quantize. For an n-bit analog-to-digital converter with a full-scale voltage of V, the formula for the minimum analog voltage change that can be distinguished is: Where LSB is the least significant bit and V is the full-scale voltage of the analog-to-digital converter.

8. The analog-to-digital conversion method applied to a column-level analog-to-digital converter according to claim 4, characterized in that: When working, the comparator compares two analog input signals and outputs a high level or a low level signal. The comparator can be composed of an open-loop operational amplifier. Ideally, when the difference between the signals at the in-phase input and the inverting input of the comparator is positive, the comparator outputs a high level, and when the difference between the signals is negative, the comparator outputs a low level.

9. The analog-to-digital conversion method applied to a column-level analog-to-digital converter according to claim 8, characterized in that: When the comparator needs to output a high level, the counter is used to complete the quantization of 1LSB, and the quantization speed of the counter depends on the frequency of the main clock.

10. The analog-to-digital conversion method applied to a column-level analog-to-digital converter according to claim 1, characterized in that: The final digital output data in step 6) can be transmitted to a microcontroller, FPGA, or other digital system via a digital bus for further processing and analysis.

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