By David Herres
We straddle two realms, analog and digital. The output of a sensor, musical instrument, the human voice, and most of the signals that originate in the real world are analog. Today most information processing is digital. This works well in terms of audio and video quality, but analog data must be converted by an analog-to-digital converter (ADC) and back to analog by a digital-to-analog converter (DAC). These two processes are mirror images of one another but they are accomplished in far different ways. In this article we’ll take a look at ADCs and in the next article, DACs.
有许多方法可以将模拟数据转换为数字，但是所有ADC相对准确，快速地完成相同的目标。此过程发生的方式随不同类型的ADC而变化。他们的共同点是，他们以离散的时间间隔采样模拟信号幅度，并将二进制数分配给每个快照中的每个快照。
Later, after processing and storage in memory, the digital signal must be reconstituted in analog form. This takes place by assembling the digital snapshots in temporal order and interpolating between them to recreate the original analog signal as modified while in digital form.
当今广泛使用的ADC类型是：
Direct(flash)转换。This protocol uses a number of comparators, each wired across a resistor that is part of a voltage divider. Each comparator samples the analog signal continuously and generates a logical 0 or 1 depending on whether the measured voltage is above or below a reference voltage of the resistor tap. (Modern devices may use active elements in place of the resistors.) This simultaneous operation makes the conversion process fast but a large number of comparators are needed to synthesize meaningful numbers of bits. Thus the implementation is expensive and sometimes unreliable.
Successive approximation。这是一种ADC，它使用单个比较器来逐步回归本地DAC的输出。基本上，DAC会产生一个模拟输出，该输出升高，直到其等于要测量的模拟输入的输出。与此级别相对应的数字代码成为模拟输入的表示。因此，采取多个步骤来获取具有指定分辨率的数字产品。
坡道电压比较器（又名集成ADC）。The ADC synthesizes a ramp waveform that is continually compared to the analog input, producing a digital solution at the correct level.
其他常见的ADC类型是Wilkinson ADC，Delta编码的ADC，子范围量化器，Sigma-Delta ADC和时间间隔ADC。这些中的每一个都涉及各种复杂程度的转化方案。它们是作为集成电路制造的。通过咨询数据表，我们可以将规格与预期的应用程序匹配，并以此为基础设计整体设备。
Obviously some anticipated uses such as for the audio channels of an oscilloscope are demanding in terms of bandwidth and reliability. Many choices are available.
帖子模数转换器的基础知识首先出现Test & Measurement Tips。
Filed Under:Test & Measurement Tips
