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overview
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Analog-to-digital converters (ADCs) convert analog quantities—which characterize most phenomena in the real world—into digital language for use in information processing, computing, data transmission, and control systems. A digital-to-analog converter (DAC) is used to convert transmitted or stored data, or the result of digital processing, into real-world variables for control, display information, or further analog processing.
overall architecture process
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Regardless of its source, an analog input variable is usually converted to a voltage or current by a sensor. These electrical quantities can take the form of: (1) fast or slow DC continuous direct measurements of a phenomenon in the time domain; (2) modulated AC waveforms (using various modulation techniques); (3) or Some kind of combination that represents the axis angles in terms of the spatial configuration of the associated variables. Examples of the first form are thermocouples, potentiometers on dc references, and outputs of analog arithmetic circuits; "chopped" optical measurements, ac strain gage or bridge outputs, digital signals embedded in noise, etc. belong to the second ; Synchro and resolver belong to the third category
Explanation of technical terms
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technical details
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The analog variables discussed in this article are those that represent actual analog phenomena in terms of voltage or current. They can be wideband or narrowband; they can be a scaled form of direct measurement, or undergo some form of analog preprocessing such as linearization, combining, demodulation, filtering, sample-and-hold, etc. During processing, the voltage and current are "normalized" to a range compatible with the specified ADC input range. The DAC's analog output voltage or current is a normalized DC signal, but may then be post-processed (eg, trimmed, filtered, amplified, etc.).
Information in digital form is typically represented by an arbitrary fixed voltage level referenced to "ground," either present at the output of a logic gate or applied to its input. The digital values used are basically binary, i.e. each "bit" (unit of information) has two possible states: one is "off", "false" or "0" and the other is "on", " true" or "1". These two logic states can also be represented by two different current levels, but using current is far less common than using voltage. In addition, there is no particular reason that the voltage must be referenced to ground. Emitter-coupled logic (ECL), positive-emitter-coupled logic (PECL), and low-voltage differential signaling logic (LVDS), etc., are not ground-referenced. A "word" is a set of levels representing a digital value, and these levels can occur in various ways: "parallel" simultaneously on a bus or a set of gate I/Os, "serial" (in some chronological order) Appears on a wire, or as a series of parallel bytes (i.e. "serial bytes")/nibbles (little bytes). For example, a 16-bit word can occupy 16 bits of a 16-bit bus, or it can be divided into two bytes that appear consecutively on an 8-bit bus, or four 4-bit nibbles that appear consecutively on a 4-bit bus superior.
While there are various logic systems, the most widely used is TTL (transistor-to-transistor logic), where "true" or 1 corresponds to a minimum output level of +2.4V (for levels above 2.0V, the input responds unambiguously is 1), False or 0 corresponds to a maximum output level of +0.4V (for levels below +0.8V, the input responds unambiguously as 0). It should be noted that although CMOS is more popular than TTL today, CMOS logic levels are generally compatible with older TTL logic standards.
For each quantized analog level, a unique set of parallel or serial digital levels (or values, codes, representing a unique portion of the analog range) is assigned. A typical numeric code looks like the following array: a7a6a5a4a3a2a1a0=10111001 It consists of 8 bits, the leftmost "1" is called the most significant bit (MSB or bit 1) and the rightmost "1" is called the least significant bit (LSB or Nth bit, which is bit 8 in this example). The code may represent a numerical value, a character, or an analog variable. To know its exact meaning, the code and conversion relationship must be defined. Be careful not to confuse the name of a particular bit (ie, bit 1, bit 2, etc.) with the subscripts of the 'a' array; subscripts correspond to powers of 2, which relate to the weight of a particular bit in the sequence.
summary
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The most familiar encoding (other than decimal) is natural or straight binary. Binary codes are most commonly used to represent integers; in an N-bit natural binary integer code, the LSB has a weight of 2 0 (ie 1), the next bit has a weight of 2 1 (ie 2), and so on up to the MSB, which has a weight of is 2 N–1 (that is, 2 N /2). The value of a binary number is obtained by adding the weights of all non-zero bits. The weighted bits are added to produce a unique number with a value in the range 0 to 2 N–1. Each additional trailing zero bit (if any) doubles the size of the number.