Analog-to-digital converter

An analog-to-digital converter (abbreviated ADC, A/D, or A to D) is a device that converts continuous signals to discrete digital numbers. The reverse operation is performed by a digital-to-analog converter (DAC). Typically, an ADC is an electronic device that converts a voltage to a binary digital number. However, some non-electronic devices, such as shaft encoders, can be considered as ADCs. Analog-to-digital converter - Resolution. The resolution of the converter indicates the ...

Including:

• Analog-to-digital converter - Resolution
• Analog-to-digital converter - Response type
• Analog-to-digital converter - Linear ADCs
• Analog-to-digital converter - Non-linear ADCs
• Analog-to-digital converter - Accuracy
• Analog-to-digital converter - Sampling rate
• Analog-to-digital converter - Aliasing
• Analog-to-digital converter - Dither
• Analog-to-digital converter - Oversampling
• Analog-to-digital converter - ADC structures
• Analog-to-digital converter - Application to music recording
• Analog-to-digital converter - Other applications

Read more here: » Analog-to-digital converter: Encyclopedia - Analog-to-digital converter

These are the most common ways of implementing an electronic ADC: A direct conversion ADC or flash ADC has a comparator that fires for each decoded voltage range. The comparator bank feeds a logic circuit that generates a code for each voltage range. Direct conversion is very fast, but usually has only 8 bits of resolution (256 comparators) or less, as it needs a large, expensive circuit. ADCs of this type have a large die size, a high input capacitance, and are prone to produce glitches on the output (by outputtin ...

See also:

Analog-to-digital converter, Analog-to-digital converter - Resolution, Analog-to-digital converter - Response type, Analog-to-digital converter - Linear ADCs, Analog-to-digital converter - Non-linear ADCs, Analog-to-digital converter - Accuracy, Analog-to-digital converter - Sampling rate, Analog-to-digital converter - Aliasing, Analog-to-digital converter - Dither, Analog-to-digital converter - Oversampling, Analog-to-digital converter - ADC structures, Analog-to-digital converter - Application to music recording, Analog-to-digital converter - Other applications

Read more here: » Analog-to-digital converter: Encyclopedia II - Analog-to-digital converter - ADC structures

The history of the digital starts with the development of the number 0 (see 0 (number)) by the Babylonians about 2000BC. Around 1620, Francis Bacon researches the first binary alphabet for representing numbers and alphabetic characters. The intended use was to establish secret communication for e.g. cities under siege and armies abroad. Leibniz was the first mathematician to develop calculations in the binary system. According to some sources, John Napier had developed binary calculations even earlier. Yet, it remains to Leibniz to first thi ...

See also:

Digital media, Digital media - History, Digital media - Digital and analogue data, Digital media - Working with digital media, Digital media - Examples of digital media

Read more here: » Digital media: Encyclopedia II - Digital media - History

The simplest and best-known form of quantization is referred to as scalar quantization, since it operates on scalar (as opposed to multi-dimensional vector) input data. In general, a scalar quantization operator can be represented as where x is a real number, is the floor function, yielding the integer f(x) and See also:

Quantization signal processing, Quantization signal processing - Mathematical description, Quantization signal processing - Quantization and data compression, Quantization signal processing - Relation to quantization in nature

Read more here: » Quantization signal processing: Encyclopedia II - Quantization signal processing - Mathematical description

Synchronous circuit design techniques make digital circuits that are immune to the failure modes that can be caused by metastability. A "clock domain" is defined as a group of flip flops with a common clock. Such architectures can form a circuit guaranteed free of metastability (below a certain maximum clock frequency, above which first metastability, then outright failure occur). When synchronous design techniques are used, protection against metastable events causing systems failures need only be provided when transferring data betw ...

See also:

Metastability in electronics, Metastability in electronics - Flip-flops, Metastability in electronics - Arbiters, Metastability in electronics - Synchronous circuits, Metastability in electronics - Failure modes

Read more here: » Metastability in electronics: Encyclopedia II - Metastability in electronics - Synchronous circuits

Adaptive optics is a technology to improve the performance of (usually) astronomical telescopes by reducing the effects of atmospheric distortion, or astronomical seeing. Adaptive optics works by measuring the distortion and rapidly compensating for it either using deformable mirrors or material with variable refractive properties. While the technique was theoretically understood for some time, it was only advances in computer technology during the 1990s that finally made the technique practical. Adaptive optics should not be confused ...

Including:

• Adaptive optics - Introduction
• Adaptive optics - Uses of adaptive optics
• Adaptive optics - Beam stabilization

Read more here: » Adaptive optics: Encyclopedia - Adaptive optics

At the most fundamental level, all physical quantities are quantized. This is a result of quantum mechanics (see Quantization (physics)). Signals may be treated as continuous for mathematical simplicity by considering the small quantizations as negligible. In any practical application, this inherent quantization is irrelevant. First of all, it is overshadowed by signal noise, the intrusion of extraneous phenomena present in the system upon the signal of interest. The seco ...

See also:

Quantization signal processing, Quantization signal processing - Mathematical description, Quantization signal processing - Quantization and data compression, Quantization signal processing - Relation to quantization in nature

Read more here: » Quantization signal processing: Encyclopedia II - Quantization signal processing - Relation to quantization in nature

As metastability is well understood and architectural techniques to control it are known, why does it persist as a failure mode in equipment? Serious computer and digital hardware bugs caused by metastability have a fascinating social history. Many engineers have refused to believe that a bistable device can enter into a state that is neither "true" nor "false" and has a positive probability that it will remain indefinite for any given period of time, albeit with exponentially decreasing probability over time. Yet metastability is an ...

See also:

Metastability in electronics, Metastability in electronics - Flip-flops, Metastability in electronics - Arbiters, Metastability in electronics - Synchronous circuits, Metastability in electronics - Failure modes

Read more here: » Metastability in electronics: Encyclopedia II - Metastability in electronics - Failure modes

AD or ad may stand for: .ad, the ccTLD (Internet Top Level Domain) for Andorra AD, the 2-letter ISO 3166-1 country code for Andorra Assistant director Alzheimer's disease Artium Doctor (Doctor of Arts) Media Arrested Development (TV Series), a Fox Network TV program Algemeen Dagblad, a Dutch newspaper. History Civilization of 'Ad, mentioned in the Quran.

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Quantization plays a major part in lossy data compression. In many cases, quantization can be viewed as the fundamental element that distinguishes lossy data compression from lossless data compression, and the use of quantization is nearly always motivated by the need to reduce the amount of data needed to represent a signal. In some compression schemes, like MP3 or Vorbis, compression is also achieved by selectively discarding some data, an action that can be analyzed as a quantization process (e.g., a ...

See also:

Quantization signal processing, Quantization signal processing - Mathematical description, Quantization signal processing - Quantization and data compression, Quantization signal processing - Relation to quantization in nature

Read more here: » Quantization signal processing: Encyclopedia II - Quantization signal processing - Quantization and data compression

Converting an analog source to digital data is done with two steps: sampling, which changes the source to a series of discrete values (called samples), and quantization, which converts each sample to a number. For example, the sensor of a digital camera contains millions of sensing elements (one for each pixel). When an exposure is made, the light focused on the array is converted into millions of electric charges (sampled). These charges are then amplified and converted to numbers (quantized). The resulting digital image is then proc ...

See also:

Digital, Digital - Analog to digital conversion, Digital - Symbol to digital conversion, Digital - Historical digital systems

Read more here: » Digital: Encyclopedia II - Digital - Analog to digital conversion

When light from a star or another astronomical object enters the Earth's atmosphere, turbulence introduced (for example, by different temperature layers and different wind speeds interacting) distort and move the image in various ways (see astronomical seeing for a full discussion). Images produced by any telescope larger than a few centimeters are blurred by these distortions. For example, a 2.5 m telescope is reduced in resolution by a factor of between 7 and 20; in the case of very large telescopes (8-10 m) (like the VLT or Keck), which are theoretically capable of milli-arcsecond ...

See also:

Adaptive optics, Adaptive optics - Introduction, Adaptive optics - Uses of adaptive optics, Adaptive optics - Beam stabilization

Read more here: » Adaptive optics: Encyclopedia II - Adaptive optics - Introduction

Since symbols are not continuous, converting symbols to digital is simpler and less prone to data loss than analog to digital conversion. Instead of sampling and quantization, similar steps are used: polling and encoding. A symbol input device usually consists of a number of switches that are polled at regular intervals to see which switches are pressed. Data will be lost if, within a single polling interval, two switches are pressed, or a switch is pressed, released, and pressed again. This polling can be done by a specialized proces ...

See also:

Digital, Digital - Analog to digital conversion, Digital - Symbol to digital conversion, Digital - Historical digital systems

Read more here: » Digital: Encyclopedia II - Digital - Symbol to digital conversion

A rather simple example is the stabilization of the position and direction of laser beam between modules in a large free space optical communication system. Fourier optics is used to control both direction and position. The actual beam is measured by photo diodes. This signal is fed into some Analog-to-digital converters and a microcontroller runs a PID controller algorithm. The controller drives some digital-to-analog converters which drive stepper motors attached to mirror mounts. If the beam is to be centered onto 4-quadrant diodes, no Analog-to-digital conve ...

See also:

Adaptive optics, Adaptive optics - Introduction, Adaptive optics - Uses of adaptive optics, Adaptive optics - Beam stabilization

Read more here: » Adaptive optics: Encyclopedia II - Adaptive optics - Beam stabilization

In A to D converters, performance can be improved using dither. This is a very small amount of random noise (white noise) which is added to the input before conversion. Its amplitude is set to be about half of the least significant bit. Its effect is to cause the state of the LSB to randomly oscillate between 0 and 1 in the presence of very low levels of input, rather than sticking at a fixed value. Rather than the signal simply getting cut off altogether at this low level (which is only being quantized to a resolution of 1 bit), it extends ...

See also:

Analog-to-digital converter, Analog-to-digital converter - Resolution, Analog-to-digital converter - Response type, Analog-to-digital converter - Linear ADCs, Analog-to-digital converter - Non-linear ADCs, Analog-to-digital converter - Accuracy, Analog-to-digital converter - Sampling rate, Analog-to-digital converter - Aliasing, Analog-to-digital converter - Dither, Analog-to-digital converter - Oversampling, Analog-to-digital converter - ADC structures, Analog-to-digital converter - Application to music recording, Analog-to-digital converter - Other applications

Read more here: » Analog-to-digital converter: Encyclopedia II - Analog-to-digital converter - Dither

ADCs are integral to much current music reproduction technology, since much music production is done on computers; even when analog recording is used, an ADC is still needed to create the PCM data stream that goes onto a compact disc. The current crop of AD converters utilized in music can sample at rates up to 192 kilohertz. Many people in the business consider this an overkill and pure marketing hype, due to the Nyquist-Shannon sampling theorem. Simply put, they say the analog waveform does not have enough information in it to neces ...

See also:

Analog-to-digital converter, Analog-to-digital converter - Resolution, Analog-to-digital converter - Response type, Analog-to-digital converter - Linear ADCs, Analog-to-digital converter - Non-linear ADCs, Analog-to-digital converter - Accuracy, Analog-to-digital converter - Sampling rate, Analog-to-digital converter - Aliasing, Analog-to-digital converter - Dither, Analog-to-digital converter - Oversampling, Analog-to-digital converter - ADC structures, Analog-to-digital converter - Application to music recording, Analog-to-digital converter - Other applications

Read more here: » Analog-to-digital converter: Encyclopedia II - Analog-to-digital converter - Application to music recording

All ADCs work by sampling their input at discrete intervals of time. Their output is therefore an incomplete picture of the behaviour of the input. There is no way of knowing, by looking at the output, what the input was doing between one sampling instant and the next. If the input is known to be changing slowly compared to the sampling rate, then it can be assumed that the value of the signal between two sample instants was somewhere between the two sampled values. If, however, the input signal is changing fast compare ...

See also:

Analog-to-digital converter, Analog-to-digital converter - Resolution, Analog-to-digital converter - Response type, Analog-to-digital converter - Linear ADCs, Analog-to-digital converter - Non-linear ADCs, Analog-to-digital converter - Accuracy, Analog-to-digital converter - Sampling rate, Analog-to-digital converter - Aliasing, Analog-to-digital converter - Dither, Analog-to-digital converter - Oversampling, Analog-to-digital converter - ADC structures, Analog-to-digital converter - Application to music recording, Analog-to-digital converter - Other applications

Read more here: » Analog-to-digital converter: Encyclopedia II - Analog-to-digital converter - Aliasing

The analog signal is continuous in time and it is necessary to convert this to a flow of digital values. It is therefore required to define the rate at which new digital values are sampled from the analog signal. The rate of new values is called the sampling rate or sampling frequency of the converter. A continuously varying bandlimited signal can be sampled (that is, the signal values at intervals of time T, the sampling time, are measured and stored) and then the original signal can be exactly reproduced from th ...

See also:

Analog-to-digital converter, Analog-to-digital converter - Resolution, Analog-to-digital converter - Response type, Analog-to-digital converter - Linear ADCs, Analog-to-digital converter - Non-linear ADCs, Analog-to-digital converter - Accuracy, Analog-to-digital converter - Sampling rate, Analog-to-digital converter - Aliasing, Analog-to-digital converter - Dither, Analog-to-digital converter - Oversampling, Analog-to-digital converter - ADC structures, Analog-to-digital converter - Application to music recording, Analog-to-digital converter - Other applications

Read more here: » Analog-to-digital converter: Encyclopedia II - Analog-to-digital converter - Sampling rate

Analog-to-digital converter - Linear ADCs. Most ADCs are of a type known as linear, although analog-to-digital conversion is an inherently non-linear process (since the mapping of a continuous space to a discrete space is a non-invertible and therefore non-linear operation). In the sense of the term "linear" as used here, it means that the range of the input values that map to each output value has a linear relationship with the output value, i.e., that the output value k is used for the range of input values fro ...

See also:

Analog-to-digital converter, Analog-to-digital converter - Resolution, Analog-to-digital converter - Response type, Analog-to-digital converter - Linear ADCs, Analog-to-digital converter - Non-linear ADCs, Analog-to-digital converter - Accuracy, Analog-to-digital converter - Sampling rate, Analog-to-digital converter - Aliasing, Analog-to-digital converter - Dither, Analog-to-digital converter - Oversampling, Analog-to-digital converter - ADC structures, Analog-to-digital converter - Application to music recording, Analog-to-digital converter - Other applications

Read more here: » Analog-to-digital converter: Encyclopedia II - Analog-to-digital converter - Response type

Accuracy depends on the error in the conversion. If the ADC is not broken, this error has two components: quantization error and (assuming the ADC is intended to be linear) non-linearity. These errors are measured in a unit called the LSB, which is an abbreviation for least significant bit. In the above example of an eight-bit ADC, an error of one LSB is 1/256 of the full signal range, or about 0.4%. Quantization error is due to the finite resolution of the ADC, and is an unavoidable imperfection in all types of ADC. The magnitude of the quantization error at t ...

See also:

Analog-to-digital converter, Analog-to-digital converter - Resolution, Analog-to-digital converter - Response type, Analog-to-digital converter - Linear ADCs, Analog-to-digital converter - Non-linear ADCs, Analog-to-digital converter - Accuracy, Analog-to-digital converter - Sampling rate, Analog-to-digital converter - Aliasing, Analog-to-digital converter - Dither, Analog-to-digital converter - Oversampling, Analog-to-digital converter - ADC structures, Analog-to-digital converter - Application to music recording, Analog-to-digital converter - Other applications

Read more here: » Analog-to-digital converter: Encyclopedia II - Analog-to-digital converter - Accuracy