Digital-electronics 简明教程
Analog to Digital Converter
一个 analog-to-digital converter ，也被称为 ADC ，是一个用于将模拟信号转换为数字格式的数字电路。
An analog-to-digital converter, also known as ADC, is a digital circuit used to convert analog signals into digital format.
将模拟信号转换为数字格式对于借助数字系统（如微处理器、微控制器、数字信号处理器 (DSP) 等）进行处理至关重要。因此，ADC 是计算机和其他数字设备等多个数字系统中的重要组成部分。
The conversion of analog signals into digital format is crucial for their processing with the help of digital systems like microprocessors, microcontrollers, digital signal processors (DSPs), etc. Therefore, ADCs are important components in several digital systems like computers and other digital devices.
在本章中，我们将详细解释模拟数字转换器的概念、组成部分、类型和应用。
In this chapter, we will explain in detail the concept, components, types, and applications of analog to digital converters.
What is an Analog to Digital Converter?
模数转换器是一种用于执行将模拟信号转换为数字数据格式的转换的数字电路。它也称为 ADC。模拟数字转换器是数字系统（如计算机、数据处理器、数字通信系统等）中的基本组成部分。
An analog to digital converter is a digital circuit designed to perform conversion of analog signals into digital data format. It is also known ADC. Analog to digital converters are essential components in digital systems like computers, data processors, digital communication systems, etc.
下图描绘了 block diagram of an analog to digital converter -
The following figure depicts the block diagram of an analog to digital converter −
从该图中可以清楚地看出，模数转换器的输入是一个模拟或自然信号，而输出是一个数字或离散时间信号。
From this figure, it is clear that the input to an analog to digital converter is an analog or natural signal and the output is a digital or discrete time signal.
在实际系统中，模数转换器作为外部环境和数字系统之间的接口。
In practical systems, the analog to digital converter serves as an interface between external environment and a digital system.
Working of Analog to Digital Converter
模数转换器的工作涉及下面解释的过程 -
The working of an analog to digital converter involves the processes explained below −
Inputting Analog Signal
模数转换器将模拟信号作为输入。模拟信号可以是电压、电流、温度、压力或任何其他随时间连续变化的物理量。
An analog to digital converter takes an analog signal as input. The analog signal could be a voltage, current, temperature, pressure, or any other physical quantity that changes continuously with time.
Sampling
在这个阶段，模数转换器以常规的时间间隔对输入模拟信号进行采样。这些时间间隔以采样率的形式定义。
At this stage, the analog to digital converter samples the input analog signal at regular intervals of time. These time intervals are defined in terms of sampling rate.
在采样过程中，持续随时间变化的模拟信号在离散的时间点进行测量，以收集信号的离散值。
In the sampling process, the analog signal that varies continuously over time is measured at discrete instants of time to collect discrete values of the signal.
Quantization
量化是将数字或离散值分配给模拟信号的每个采样值的过程。在量化过程中，所有可能的模拟值的范围被划分为有限数量的离散数字值。
Quantization is a process of assigning a digital or discrete value to each sampled value of the analog signal. In the process of quantization, the range of all possible analog values is divided into a finite number of discrete digital values.
Encoding
编码是将量化的数字值转换为其等效二进制数的过程。这些编码的二进制数以数字格式表示采样的模拟值。
Encoding is a process of converting the quantized digital values into their equivalent binary numbers. These encoded binary numbers represent the sampled analog values in the digital format.
模数转换器的分辨率、准确性和精确性由用于编码的比特数决定。
The resolution, accuracy, and precision of the analog to digital converter is determined by the number of bits used for encoding.
Performance Factors of Analog to Digital Converters
模数转换器的性能可以使用几个不同因素来评估。以下两个是最重要的：
The performance of an analog to digital converter can be evaluated using several different factors. The following two are the most important −
Signal-to-Noise Ratio (SNR) of ADC
模数转换器的信噪比 (SNR) 被定义为转换器区分所需信号和不需要的噪音信号的能力的度量。
The Signal-to-Noise Ratio (SNR) of an analog to digital converter is defined as the measure of ability of the converter to differentiate between the desired signal and unwanted noise signal.
在数学上，模数转换器的 SNR 表示为电信号（表示有用信息）的功率与噪音信号（表示不需要的干扰）的功率之比。
Mathematically, the SNR of an analog to digital converter is expressed as the ratio of the power of the electrical signal (that represents the useful information) to the power of the noise signal (that represents the unwanted disturbances).
在实践中，SNR 以分贝 (dB) 表示，计算 ADC 的 SNR 的公式如下所示，
In practice, the SNR is expressed in decibels (dB) and the formula for calculating the SNR of an ADC is given below,
\mathrm{SNR \: of \: ADC \: = \: 10 \: \times \: log ( \frac{Electrical \: Signal \: Power}{Noise \: Signal \: Power})}
从这个表达式可以看出，更高的 SNR 表示模数转换器的性能更好。换句话说，具有高 SNR 的模数转换器可以更清楚地区分电信号和噪声信号。因此，模数转换器具有高 SNR 是可取的，以便它即使在存在噪声信号的情况下也能准确地捕获和数字化较小的模拟信号。
From this expression, it is clear that a higher SNR represents better performance of the analog to digital converter. In other words, an analog to digital converter having a high SNR distinguishes the electrical signal from the noise signal more clearly. Therefore, it is desirable that the analog to digital converter have a high SNR so that it can accurately capture and digitalize smaller analog signals even in the presence of noise signals.
Bandwidth of Analog to Digital Converter
模数转换器的带宽只不过是它可以准确采样和数字化的频率范围。模数转换器的采样率决定了它的带宽。其中，采样率定义为每秒获取的模拟信号样本数。
The bandwidth of an analog to digital converter is nothing but the range of frequencies that it can sample and digitalize accurately. The sampling rate of the analog to digital converter determines its bandwidth. Where, the sampling rate is defined as the number of samples of the analog signal taken per second.
根据奈奎斯特-香农采样定理，模数转换器的最大采样率应至少是输入模拟信号中存在的最大频率分量的两倍。这是一个重要的因素，可以避免信号误识别，从而导致采样中的失真或错误。
According to the Nyquist-Shannon sampling theorem, the maximum sampling rate of an analog to digital converter should be at least double of the maximum frequency component present in the input analog signal. It is an important factor to avoid misidentification of the signal that can introduce distortion or error in sampling.
我们举一个例子来理解这一点，考虑一个最大采样率为 150 kHz 的模数转换器，那么它的带宽应限制在小于 75 kHz 的频率，以防止失真。
Let us take an example to understand this, consider an analog to digital converter having a maximum sampling rate of 150 kHz, then its bandwidth should be limited to frequencies less than 75 kHz to prevent distortion.
因此，重要的是模数转换器应具有足够的带宽以准确捕获高频模拟信号。
Hence, it is important that the analog to digital converter should have a sufficient bandwidth to capture the high-frequency analog signals accurately.
Types of Analog-to-Digital Converters
在数字电子学中，设计了不同类型的模数转换器 (ADC) 以满足不同应用的要求，一些常见的模数转换器类型包括以下：
In digital electronics, different types of analog-to-digital converters (ADCs) are designed to fulfil the requirements of different applications.Some of common types of analog-to-digital converters include the following −
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Flash ADC
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Semi-Flash ADC
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Successive Approximation Register ADC
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Sigma-Delta ADC
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Pipelined ADC
Flash ADC
Flash ADC ，也称为 Direct ADC ，是最快的 ADC。这种类型的 ADC 具有吉赫兹级别的采样率。闪速 ADC 提供如此高的速度，因为它们使用一组可以并行操作的比较器，每个比较器针对特定的电压范围。
Flash ADC, also known as Direct ADC, is the fastest ADC available. This type of ADC has sampling rates of the order of gigahertz. The flash ADCs offer such high speeds because they use a bank of comparators that can operate in parallel, each for a certain voltage range.
然而，闪速 ADC 的尺寸相对较大，成本也高于其他类型的 ADC。此外，它们的功耗也相对较高。对于闪速 ADC，如果 ADC 的分辨率是“n 位”，那么它在组中需要 (2n – 1) 个比较器。例如，一个具有 8 位分辨率的闪速 ADC 需要 (28 – 1 = 255) 个比较器。
However, the flash ADCs are relatively larger in size and costlier than other types of ADCs. Also, they consume relatively more power. In the case of a flash ADC, if "n bits" is resolution of the ADC, then it requires (2n – 1) comparators in its bank. For example, a flash ADC having 8-bit resolution requires (28 – 1 = 255) comparators.
闪速模数转换器主要用于视频信号或光存储中的快速信号的数字化。
The flash analog-to-digital converters are mainly used in digitization of video signals or fast signals in optical storage.
Semi-Flash ADC
半闪速 ADC 是一种模数转换器，它将闪速 ADC 的快速速度与数量减少的比较器结合在一起。这两个特性使半闪速 ADC 的尺寸紧凑、成本低于闪速 ADC。
The Semi-Flash ADC is a type of analog-to-digital converter that combines the fast speed of a flash ADC with a reduced number of comparators. These two features together make the semi-flash ADC compact in size and cost effective as compared to a flash ADC.
在半闪速模数转换器中，使用两个单独的并行工作的闪速转换器。每个转换器的分辨率均为整个半闪速 ADC 位数的一半。一个转换器处理信号的最有效位 (MSB)，而另一个转换器处理信号的最低有效位 (LSB)。
In a semi-flash analog to digital converter, two separate flash converters are used that operate in parallel. Each converter has a resolution that is half the number of bits of the whole semi-flash ADC. One converter handles the most significant bits (MSBs) and the other converter handles the least significant bits (LSBs) of the signal.
在处理之后，两个转换器产生的输出将进行组合，生成半闪速 ADC 的最终数字输出。
After processing, the outputs produced by the two converters are combined to generate the final digital output of the semi-flash ADC.
半闪速模数转换器最显著的优势是，它在保持高速运行的同时，所需比较器数量少于普通闪速 ADC。这会减小其尺寸，降低复杂性和成本。然而，它需要更多时间来完成转换过程，因为它需要一些额外时间来组合两个分离转换器的部分结果。
The most significant advantage of the semi-flash analog to digital converter is that it requires a lesser number of comparators than an ordinary flash ADC with maintaining the high-speed operation. This results in smaller size, reduced complexity and cost. However, it takes more time to complete the conversion process because it requires some additional time to combine the partial results of the two separate converters.
半闪速模数转换器广泛用于需要平衡速度、分辨率和成本的应用中。
The semi-flash analog-to-digital converters are widely used in applications that require a balance between speed, resolution, and cost.
Successive Approximation Register ADC
连续逼近寄存器模数转换器，缩写为 SAR ADC，是一种模数转换器，它使用一系列的比较来确定数字输出的每个位。
The Successive Approximation Register Analog to Digital Converter, abbreviated as SAR ADC, is a type of analog to digital converter that uses a series of comparisons to determine each bit of the digital output.
SAR ADC 首先通过初始化其内部近似寄存器开始工作。然后，它对输入模拟信号进行采样，并将其存储稳定，直到转换过程完成。
The SAR ADC starts working by initializing its internal approximation registers. Then, it takes a sample of the input analog signal and stores it steady until the conversion process completes.
之后，利用二分搜索算法来执行输入信号的近似。此过程首先将输出数字信号的最有效位 (MSB) 设置为最高值，并将此值与采样的输入模拟信号进行比较。
After that a binary search algorithm is utilized to perform approximation of the input signal. This process starts by setting the most significant bit (MSB) of the output digital signal to the highest value and compares this value with the sampled input analog signal.
在下一步中，SAR ADC 将采样的输入模拟信号与内部数模转换器的输出进行比较，该转换器会产生与输入信号的当前近似值成比例的信号。
In the next step, the SAR ADC compares the sampled input analog signal with the output of an internal digital-to-analog converter that produces a signal proportional to the current approximation of the input signal.
根据比较结果，SAR ADC 连续更改数字输出中每个位的数值，直至获得所需的输出。一旦确定数字输出的所有位，SAR 转换器即完成转换过程。获得的数字输出表示采样的输入模拟信号的数字近似值。
Depending on results of the comparison, the SAR ADC successively changes the value of each bit in the digital output until the desired output is obtained. Once all bits of the digital output have been determined, the SAR converter completes the conversion process. The digital output obtained represents the digital approximation of the sampled input analog signal.
SAR 模数转换器通常用于各种应用，例如消费电子产品、医疗仪器、数据采集系统等。
The SAR analog-to-digital converters are commonly used in various applications, such as consumer electronics, medical instruments, data acquisition systems, etc.
Sigma-Delta ADC
Sigma-Delta 模数转换器，也表示为 ΣΔ ADC，是一种模数转换器，它提供高分辨率，并且用于需要精确测量和信号处理的应用，例如录音、高质量音频系统、基于传感器的系统、精密仪器等。
The Sigma-Delta Analog-to-Digital Converter, also represented as ΣΔ ADC, is a type of analog to digital converter that provides a high resolution and is used in applications that require precise measurement and signal processing like in audio recording, high-quality audio systems, sensor-based systems, precise instruments, etc.
working of a sigma-delta ADC 包含以下过程−
The working of a sigma-delta ADC involves the following processes −
首先，它以显著高于奈奎斯特速率的频率对模拟输入信号进行采样，以获取更多有关输入信号的信息。此过程称为过采样。
First, it samples the analog input signal at a frequency significantly higher than the Nyquist rate to capture more information about the input signal. This process is called oversampling.
然后，使用三角调制将过采样模拟信号转换成一系列数字脉冲。在三角调制过程中，模拟输入信号的连续采样之间的差值或三角值被量化并转换成数字形式。
Then, delta modulation is used to convert the oversampled analog signal into a series of digital pulses. In the process of delta modulation, the difference or delta between successive samples of the analog input signal is quantized and converted into digital form.
现在，执行 sigma-delta 调制，其中使用 sigma-delta 调制器来调制实际模拟信号与其数字形式之间的差值。在此调制中，量化噪声被从所需频带推向较高频段。
Now, the sigma-delta modulation is performed, in which a sigma-delta modulator is used to modulate the difference between the actual analog signal and its digital form. In this modulation, the quantization noise is pushed away from the desired frequency band and towards the higher frequencies.
在 sigma-delta 调制之后，数字信号被传递通过低通滤波器，从而去除过采样和 sigma-delta 调制期间引入的高频噪声。此低通滤波器通过提取低频组件来产生高分辨率数字输出。
After sigma-delta modulation, the digital signal is passed through a low-pass filter that removes the high-frequency noise that can be introduced during oversampling and sigma-delta modulation. This low-pass filter produces a high-resolution digital output by extracting the low-frequency components.
在转换过程的最后，数字信号被下采样（例如小数化），以将其采样率降低到所需的输出速率。
At the end of the conversion process, the digital signal is down-sampled (i.e., decimated) to decrease its sample rate to the desired output rate.
Pipelined ADC
流水线式模数转换器是一种 ADC，它与 SAR ADC 类似，但它执行粗略和精细转换。它在分辨率和速度之间提供平衡，使其适合在通信系统、医疗测试设备、多媒体、工业控制系统等中使用。
The Pipelined Analog to Digital Converter is a type of ADC which is similar to the SAR ADC, but it performs a coarse and refined conversion. It provides a balance between resolution and speed that make it suitable to use in communication systems, medical test equipment, multimedia, industrial control systems, etc.
流水线式 ADC 在多个阶段工作，其中每个阶段完成模数转换的特定部分。之所以称为流水线式 ADC，是因为所有阶段都以流水线方式进行，其中一个阶段的输出进入下一个阶段。
A pipelined ADC works in multiple stages, where each stage completes a specific part of the analog-to-digital conversion. It is called pipelined ADC because all stages take place in a pipeline manner, in which the output of one stage enters into the next stage.
在流水线式 ADC 中，模拟输入信号被分成多个子范围，流水线的每个阶段执行子范围的量化，以将模拟输入信号转换为数字形式。需要注意的是，流水线式 ADC 的所有阶段并行操作，以提供更快的转换速率。
In the pipelined ADC, the analog input signal is divided into multiple subranges and each stage of the pipeline performs quantization of a subrange to convert the analog input signal into digital form. It is important to note that all stages of the pipelined ADC operate in parallel to provide a faster conversion rate.
流水线式 ADC 使用各种数字校正技术，例如数字校准、错误校正算法和数字滤波器，以消除在模数转换过程中可能引入的错误。这提高了数字输出的准确性和可靠性。
The pipelined ADC uses various digital correction techniques such as digital calibration, error correction algorithms, and digital filtering to remove errors that can be introduced during the analog-to-digital conversion process. This improves the accuracy and reliability of the digital output.
这就是数字电子中一些常用的模数转换器 (ADC) 类型。
This is all about some commonly used types of analog to digital converters (ADCs) in digital electronics.
Applications of Analog to Digital Converter
模数转换器 (ADC) 用于各种行业和领域，在这些行业和领域中，模拟信号必须使用诸如计算机之类的数字系统进行处理、分析或传输。下面列出了模数转换器的某些常见应用：
Analog-to-digital converters (ADCs) are used in various industries and fields where analog signals have to be processed, analyzed, or transmitted using digital systems like computers. Some common applications of analog to digital converters are listed below −
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In the field of digital signal processing, ADCs are used for converting analog signals obtained from sensors, microphones, or other analog devices into digital format for processing them using digital processors.
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In audio processing applications, ADCs are used to convert analog audio signals into digital format for storage, manipulation, and transmission in digital systems.
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ADCs are essential components in various data acquisition systems used in the field of scientific research, industrial automation, and instrumentation.
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In communication systems, ADCs are used to convert analog audio or video signals into digital format for transmission over communication channels.
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ADCs are used in radio receivers for digitization of received radio frequency (RF) signals.
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ADCs play an important role in several medical equipment and healthcare systems for converting various analog bio-signals and physiological parameters like heart rate, blood pressure, oxygen saturation, EEG signals, etc. into digital format to process them using digital systems.
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In automotive electronics, ADCs are used to convert analog signals received from sensors measuring parameters such as temperature, torque, speed, etc. into digital format for driver assistance and vehicle diagnostics.
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ADCs are also used in a wide range of consumer electronic devices such as smartphones, tablets, laptops, entertainment equipment, etc.
这些只是模数转换器 (ADC) 在各个领域和行业中的部分应用示例。
These are a few examples of the applications of analog-to-digital converters (ADCs) in various fields and industries.
Conclusion
在本章中，我们详细解释了模数转换器、它们的类型和应用。总之，模数转换器是一种可以将模拟输入信号转换为数字输出信号的电子电路。
In this chapter, we explained in detail about analog to digital converters, their types and applications. In conclusion, an analog to digital converter is an electronic circuit that can convert an analog input signal into a digital output signal.
ADC 是跨行业使用的许多设备和系统中的重要组件。这是因为实时接收到的信号（如语音信号、传感器信号等）本质上是模拟信号，无法使用计算机等数字系统进行处理。ADC 有助于克服此接口问题。基本上，ADC 是模拟输入设备和数字处理元件之间的接口。
ADCs are important components in several devices and systems used across various industries. This is because, the signals received in real-time like voice signals, signals from sensors, etc. are analog in nature and they cannot be processed using digital systems like computers. ADCs help to overcome this interfacing issue. Basically, ADCs act as an interface between an analog input device and a digital processing element.