64-495: [REDACTED] Look up ADC in Wiktionary, the free dictionary. ADC may refer to: Science and medicine [ edit ] ADC (gene) , a human gene AIDS dementia complex , neurological disorder associated with HIV and AIDS Allyl diglycol carbonate or CR-39, a polymer Antibody-drug conjugate , a type of anticancer treatment Apparent diffusion coefficient ,
128-491: A capacitor to store the analog voltage at the input, and using an electronic switch or gate to disconnect the capacitor from the input. Many ADC integrated circuits include the sample and hold subsystem internally. An ADC works by sampling the value of the input at discrete intervals in time. Provided that the input is sampled above the Nyquist rate , defined as twice the highest frequency of interest, then all frequencies in
192-437: A digital encoder logic circuit that generates a binary number on the output lines for each voltage range. ADCs of this type have a large die size and high power dissipation. They are often used for video , wideband communications , or other fast signals in optical and magnetic storage . The circuit consists of a resistive divider network, a set of op-amp comparators and a priority encoder. A small amount of hysteresis
256-438: A saw-tooth signal that ramps up or down then quickly returns to zero. When the ramp starts, a timer starts counting. When the ramp voltage matches the input, a comparator fires, and the timer's value is recorded. Timed ramp converters can be implemented economically, however, the ramp time may be sensitive to temperature because the circuit generating the ramp is often a simple analog integrator . A more accurate converter uses
320-470: A 500 Hz sine wave. To avoid aliasing, the input to an ADC must be low-pass filtered to remove frequencies above half the sampling rate. This filter is called an anti-aliasing filter , and is essential for a practical ADC system that is applied to analog signals with higher frequency content. In applications where protection against aliasing is essential, oversampling may be used to greatly reduce or even eliminate it. Although aliasing in most systems
384-405: A Microsoft technology Advanced Direct Connect , a peer-to-peer file sharing and chat protocol Air data computer , an essential avionics component found in modern glass cockpits Analog-to-digital converter , a type of electronic circuit Android Developer Challenge , a competition Apple Developer Connection , Apple Computer's developer network Apple Display Connector , similar to
448-491: A clocked counter driving a DAC. A special advantage of the ramp-compare system is that converting a second signal just requires another comparator and another register to store the timer value. To reduce sensitivity to input changes during conversion, a sample and hold can charge a capacitor with the instantaneous input voltage and the converter can time the time required to discharge with a constant current . An integrating ADC (also dual-slope or multi-slope ADC) applies
512-525: A constant current source . The time required to discharge the capacitor is proportional to the amplitude of the input voltage. While the capacitor is discharging, pulses from a high-frequency oscillator clock are counted by a register. The number of clock pulses recorded in the register is also proportional to the input voltage. If the analog value to measure is represented by a resistance or capacitance, then by including that element in an RC circuit (with other resistances or capacitances fixed) and measuring
576-534: A derived value from a diffusion MRI Automated dispensing cabinet , a computerized drug storage device for hospitals Azodicarbonamide , a blowing agent Organisations [ edit ] Arts [ edit ] ADC Theatre , venue of the University of Cambridge Amateur Dramatic Club Art Directors Club of New York , a professional association Australian Dance Council , a national dance advocacy organisation Hong Kong Arts Development Council ,
640-422: A digital number representing the magnitude of the voltage or current. Typically the digital output is a two's complement binary number that is proportional to the input, but there are other possibilities. There are several ADC architectures . Due to the complexity and the need for precisely matched components , all but the most specialized ADCs are implemented as integrated circuits (ICs). These typically take
704-432: A faithful reproduction of the original signal is only possible if the sampling rate is higher than twice the highest frequency of the signal. Since a practical ADC cannot make an instantaneous conversion, the input value must necessarily be held constant during the time that the converter performs a conversion (called the conversion time ). An input circuit called a sample and hold performs this task—in most cases by using
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#1732764975876768-446: 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 and then the original signal can be reproduced from the discrete-time values by a reconstruction filter . The Nyquist–Shannon sampling theorem implies that
832-422: A known voltage charging and discharging curve that can be used to solve for an unknown analog value. The Wilkinson ADC was designed by Denys Wilkinson in 1950. The Wilkinson ADC is based on the comparison of an input voltage with that produced by a charging capacitor. The capacitor is allowed to charge until a comparator determines it matches the input voltage. Then, the capacitor is discharged linearly by using
896-436: A longer time to measure than smaller one. And the accuracy is limited by the accuracy of the microcontroller clock and the amount of time available to measure the value, which potentially might even change during measurement or be affected by external parasitics . A direct-conversion or flash ADC has a bank of comparators sampling the input signal in parallel, each firing for a specific voltage range. The comparator bank feeds
960-687: A peer-to-peer file sharing and chat protocol Air data computer , an essential avionics component found in modern glass cockpits Analog-to-digital converter , a type of electronic circuit Android Developer Challenge , a competition Apple Developer Connection , Apple Computer's developer network Apple Display Connector , similar to the DVI connector Application delivery controller , for accelerating website performance Automatic Data Capture , for automatic identification, data collection and storage into computer systems Other uses [ edit ] New Zealand ADC class diesel multiple unit ,
1024-580: A political party from the State of Colima, Mexico Others [ edit ] Acadia Divinity College , a seminary on the campus of Acadia University, Canada Advanced Digital Corporation , a defunct computer company of Southern California ADC Map , an American map publisher ADC Telecommunications , in Eden Prairie, Minnesota Australian Defence College , Weston Creek, Canberra Technology [ edit ] Advanced Data Connector ,
1088-580: A political party in Nigeria Alliance for Democratic Change , a political party in Tanzania American Deserters Committee , an anti-Vietnam War group American-Arab Anti-Discrimination Committee , a civil rights organization Arizona Department of Corrections , US Arkansas Department of Correction , US Ashfield District Council , Nottinghamshire, England Asociación Democrática de Colima ,
1152-464: A political party in Tanzania American Deserters Committee , an anti-Vietnam War group American-Arab Anti-Discrimination Committee , a civil rights organization Arizona Department of Corrections , US Arkansas Department of Correction , US Ashfield District Council , Nottinghamshire, England Asociación Democrática de Colima , a political party from the State of Colima, Mexico Others [ edit ] Acadia Divinity College ,
1216-445: A polymer Antibody-drug conjugate , a type of anticancer treatment Apparent diffusion coefficient , a derived value from a diffusion MRI Automated dispensing cabinet , a computerized drug storage device for hospitals Azodicarbonamide , a blowing agent Organisations [ edit ] Arts [ edit ] ADC Theatre , venue of the University of Cambridge Amateur Dramatic Club Art Directors Club of New York ,
1280-654: A professional association Australian Dance Council , a national dance advocacy organisation Hong Kong Arts Development Council , a statutory body in Hong Kong Aviation [ edit ] ADC Aircraft , a British firm established in 1920 ADC Airlines , based in Ikeja, Nigeria Aerospace Defense Command , of the U.S. Air Force Government and politics [ edit ] Aboriginal Development Commission , an Australian statutory body that existed from 1980 to 1990 African Democratic Congress ,
1344-409: A pulse of a particular amplitude is always converted to the same digital value. The problem lies in that the ranges of analog values for the digitized values are not all of the same widths, and the differential linearity decreases proportionally with the divergence from the average width. The sliding scale principle uses an averaging effect to overcome this phenomenon. A random, but known analog voltage
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#17327649758761408-454: A sampler. It cannot improve the linearity, and thus accuracy does not necessarily improve. Quantization distortion in an audio signal of very low level with respect to the bit depth of the ADC is correlated with the signal and sounds distorted and unpleasant. With dithering, the distortion is transformed into noise. The undistorted signal may be recovered accurately by averaging over time. Dithering
1472-408: A seminary on the campus of Acadia University, Canada Advanced Digital Corporation , a defunct computer company of Southern California ADC Map , an American map publisher ADC Telecommunications , in Eden Prairie, Minnesota Australian Defence College , Weston Creek, Canberra Technology [ edit ] Advanced Data Connector , a Microsoft technology Advanced Direct Connect ,
1536-474: A senior military or government person Alternative Daily cover , material other than soil for containment in a landfill Andakombe Airport , airport in Papua New Guinea (IATA: ADC) Andrew Dice Clay (born 1957), American comedian A.DC. , taxonomic author abbreviation for Alphonse Pyramus de Candolle (1806–1893), French-Swiss botanist Axiom of dependent choice Topics referred to by
1600-461: A statutory body in Hong Kong Aviation [ edit ] ADC Aircraft , a British firm established in 1920 ADC Airlines , based in Ikeja, Nigeria Aerospace Defense Command , of the U.S. Air Force Government and politics [ edit ] Aboriginal Development Commission , an Australian statutory body that existed from 1980 to 1990 African Democratic Congress , a political party in Nigeria Alliance for Democratic Change ,
1664-663: A type of diesel railway vehicle used on Auckland's suburban network Adlington (Cheshire) railway station , UK (National Rail code) Aid to Dependent Children , an American government social program from 1935 to 1960 Aide-de-camp , assistant to a senior military or government person Alternative Daily cover , material other than soil for containment in a landfill Andakombe Airport , airport in Papua New Guinea (IATA: ADC) Andrew Dice Clay (born 1957), American comedian A.DC. , taxonomic author abbreviation for Alphonse Pyramus de Candolle (1806–1893), French-Swiss botanist Axiom of dependent choice Topics referred to by
1728-454: Is a very small amount of random noise (e.g. white noise ), which is added to the input before conversion. Its effect is to randomize the state of the LSB based on the signal. Rather than the signal simply getting cut off altogether at low levels, it extends the effective range of signals that the ADC can convert, at the expense of a slight increase in noise. Dither can only increase the resolution of
1792-535: Is added to the sampled input voltage. It is then converted to digital form, and the equivalent digital amount is subtracted, thus restoring it to its original value. The advantage is that the conversion has taken place at a random point. The statistical distribution of the final levels is decided by a weighted average over a region of the range of the ADC. This in turn desensitizes it to the width of any specific level. These are several common ways of implementing an electronic ADC. Resistor-capacitor (RC) circuits have
1856-471: Is also used in integrating systems such as electricity meters . Since the values are added together, the dithering produces results that are more exact than the LSB of the analog-to-digital converter. Dither is often applied when quantizing photographic images to a fewer number of bits per pixel—the image becomes noisier but to the eye looks far more realistic than the quantized image, which otherwise becomes banded . This analogous process may help to visualize
1920-428: Is built into the comparator to resolve any problems at voltage boundaries. At each node of the resistive divider, a comparison voltage is available. The purpose of the circuit is to compare the analog input voltage with each of the node voltages. The circuit has the advantage of high speed as the conversion takes place simultaneously rather than sequentially. Typical conversion time is 100 ns or less. Conversion time
1984-487: Is characterized primarily by its sampling rate . The SNDR of an ADC is influenced by many factors, including the resolution , linearity and accuracy (how well the quantization levels match the true analog signal), aliasing and jitter . The SNDR of an ADC is often summarized in terms of its effective number of bits (ENOB), the number of bits of each measure it returns that are on average not noise . An ideal ADC has an ENOB equal to its resolution. ADCs are chosen to match
ADC - Misplaced Pages Continue
2048-442: Is different from Wikidata All article disambiguation pages All disambiguation pages ADC [REDACTED] Look up ADC in Wiktionary, the free dictionary. ADC may refer to: Science and medicine [ edit ] ADC (gene) , a human gene AIDS dementia complex , neurological disorder associated with HIV and AIDS Allyl diglycol carbonate or CR-39,
2112-503: Is different from Wikidata All article disambiguation pages All disambiguation pages Analog-to-digital converter In electronics , an analog-to-digital converter ( ADC , A/D , or A-to-D ) is a system that converts an analog signal , such as a sound picked up by a microphone or light entering a digital camera , into a digital signal . An ADC may also provide an isolated measurement such as an electronic device that converts an analog input voltage or current to
2176-427: Is limited only by the speed of the comparator and of the priority encoder. This type of ADC has the disadvantage that the number of comparators required almost doubles for each added bit. Also, the larger the value of n, the more complex is the priority encoder. A successive-approximation ADC uses a comparator and a binary search to successively narrow a range that contains the input voltage. At each successive step,
2240-459: Is the ADC's resolution in bits and E FSR is the full-scale voltage range (also called 'span'). E FSR is given by where V RefHi and V RefLow are the upper and lower extremes, respectively, of the voltages that can be coded. Normally, the number of voltage intervals is given by where M is the ADC's resolution in bits. That is, one voltage interval is assigned in between two consecutive code levels. Example: In many cases,
2304-414: Is the number of ADC bits. Clock jitter is caused by phase noise . The resolution of ADCs with a digitization bandwidth between 1 MHz and 1 GHz is limited by jitter. For lower bandwidth conversions such as when sampling audio signals at 44.1 kHz, clock jitter has a less significant impact on performance. An analog signal is continuous in time and it is necessary to convert this to
2368-407: Is uniformly distributed between − 1 ⁄ 2 LSB and + 1 ⁄ 2 LSB, and the signal has a uniform distribution covering all quantization levels, the signal-to-quantization-noise ratio (SQNR) is given by where Q is the number of quantization bits. For example, for a 16-bit ADC, the quantization error is 96.3 dB below the maximum level. Quantization error is distributed from DC to
2432-404: Is unwanted, it can be exploited to provide simultaneous down-mixing of a band-limited high-frequency signal (see undersampling and frequency mixer ). The alias is effectively the lower heterodyne of the signal frequency and sampling frequency. For economy, signals are often sampled at the minimum rate required with the result that the quantization error introduced is white noise spread over
2496-479: The Nyquist frequency . Consequently, if part of the ADC's bandwidth is not used, as is the case with oversampling , some of the quantization error will occur out-of-band , effectively improving the SQNR for the bandwidth in use. In an oversampled system, noise shaping can be used to further increase SQNR by forcing more quantization error out of band. In ADCs, performance can usually be improved using dither . This
2560-470: The bandlimited analog input signal. The resolution of the converter indicates the number of different, i.e. discrete, values it can produce over the allowed range of analog input values. Thus a particular resolution determines the magnitude of the quantization error and therefore determines the maximum possible signal-to-noise ratio for an ideal ADC without the use of oversampling . The input samples are usually stored electronically in binary form within
2624-463: The effective number of bits (ENOB) below that predicted by quantization error alone. The error is zero for DC, small at low frequencies, but significant with signals of high amplitude and high frequency. The effect of jitter on performance can be compared to quantization error: Δ t < 1 2 q π f 0 {\displaystyle \Delta t<{\frac {1}{2^{q}\pi f_{0}}}} , where q
ADC - Misplaced Pages Continue
2688-408: The signal-to-noise ratio performance of the ADC and thus reduce its effective resolution. When digitizing a sine wave x ( t ) = A sin ( 2 π f 0 t ) {\displaystyle x(t)=A\sin {(2\pi f_{0}t)}} , the use of a non-ideal sampling clock will result in some uncertainty in when samples are recorded. Provided that
2752-421: The ADC, so the resolution is usually expressed as the audio bit depth . In consequence, the number of discrete values available is usually a power of two. For example, an ADC with a resolution of 8 bits can encode an analog input to one in 256 different levels (2 = 256). The values can represent the ranges from 0 to 255 (i.e. as unsigned integers) or from −128 to 127 (i.e. as signed integer), depending on
2816-541: The DVI connector Application delivery controller , for accelerating website performance Automatic Data Capture , for automatic identification, data collection and storage into computer systems Other uses [ edit ] New Zealand ADC class diesel multiple unit , a type of diesel railway vehicle used on Auckland's suburban network Adlington (Cheshire) railway station , UK (National Rail code) Aid to Dependent Children , an American government social program from 1935 to 1960 Aide-de-camp , assistant to
2880-519: The actual sampling time uncertainty due to clock jitter is Δ t {\displaystyle \Delta t} , the error caused by this phenomenon can be estimated as E a p ≤ | x ′ ( t ) Δ t | ≤ 2 A π f 0 Δ t {\displaystyle E_{ap}\leq |x'(t)\Delta t|\leq 2A\pi f_{0}\Delta t} . This will result in additional recorded noise that will reduce
2944-409: The application. Resolution can also be defined electrically, and expressed in volts . The change in voltage required to guarantee a change in the output code level is called the least significant bit (LSB) voltage. The resolution Q of the ADC is equal to the LSB voltage. The voltage resolution of an ADC is equal to its overall voltage measurement range divided by the number of intervals: where M
3008-605: The bandwidth and required SNDR of the signal to be digitized. If an ADC operates at a sampling rate greater than twice the bandwidth of the signal, then per the Nyquist–Shannon sampling theorem , near-perfect reconstruction is possible. The presence of quantization error limits the SNDR of even an ideal ADC. However, if the SNDR of the ADC exceeds that of the input signal, then the effects of quantization error may be neglected, resulting in an essentially perfect digital representation of
3072-415: The converter compares the input voltage to the output of an internal digital-to-analog converter (DAC) which initially represents the midpoint of the allowed input voltage range. At each step in this process, the approximation is stored in a successive approximation register (SAR) and the output of the digital-to-analog converter is updated for a comparison over a narrower range. A ramp-compare ADC produces
3136-417: The effect of dither on an analog audio signal that is converted to digital. An ADC has several sources of errors. Quantization error and (assuming the ADC is intended to be linear) non- linearity are intrinsic to any analog-to-digital conversion. These errors are measured in a unit called the least significant bit (LSB). In the above example of an eight-bit ADC, an error of one LSB is 1 ⁄ 256 of
3200-442: The form of metal–oxide–semiconductor (MOS) mixed-signal integrated circuit chips that integrate both analog and digital circuits . A digital-to-analog converter (DAC) performs the reverse function; it converts a digital signal into an analog signal. An ADC converts a continuous-time and continuous-amplitude analog signal to a discrete-time and discrete-amplitude digital signal . The conversion involves quantization of
3264-499: The full signal range, or about 0.4%. All ADCs suffer from nonlinearity errors caused by their physical imperfections, causing their output to deviate from a linear function (or some other function, in the case of a deliberately nonlinear ADC) of their input. These errors can sometimes be mitigated by calibration , or prevented by testing. Important parameters for linearity are integral nonlinearity and differential nonlinearity . These nonlinearities introduce distortion that can reduce
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#17327649758763328-413: The input, so it necessarily introduces a small amount of quantization error . Furthermore, instead of continuously performing the conversion, an ADC does the conversion periodically, sampling the input, and limiting the allowable bandwidth of the input signal. The performance of an ADC is primarily characterized by its bandwidth and signal-to-noise and distortion ratio (SNDR). The bandwidth of an ADC
3392-494: The logarithm of the resolution, i.e. the number of bits. Flash ADCs are certainly the fastest type of the three; The conversion is basically performed in a single parallel step. There is a potential tradeoff between speed and precision. Flash ADCs have drifts and uncertainties associated with the comparator levels results in poor linearity. To a lesser extent, poor linearity can also be an issue for successive-approximation ADCs. Here, nonlinearity arises from accumulating errors from
3456-410: The performance of the ADC can be greatly increased at little or no cost. Furthermore, as any aliased signals are also typically out of band, aliasing can often be eliminated using very low cost filters. The speed of an ADC varies by type. The Wilkinson ADC is limited by the clock rate which is processable by current digital circuits. For a successive-approximation ADC , the conversion time scales with
3520-447: The same term [REDACTED] This disambiguation page lists articles associated with the title ADC . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=ADC&oldid=1239853298 " Categories : Disambiguation pages Political party disambiguation pages Hidden categories: Short description
3584-447: The same term [REDACTED] This disambiguation page lists articles associated with the title ADC . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=ADC&oldid=1239853298 " Categories : Disambiguation pages Political party disambiguation pages Hidden categories: Short description
3648-504: The signal can be reconstructed. If frequencies above half the Nyquist rate are sampled, they are incorrectly detected as lower frequencies, a process referred to as aliasing. Aliasing occurs because instantaneously sampling a function at two or fewer times per cycle results in missed cycles, and therefore the appearance of an incorrectly lower frequency. For example, a 2 kHz sine wave being sampled at 1.5 kHz would be reconstructed as
3712-406: The subtraction processes. Wilkinson ADCs have the best linearity of the three. The sliding scale or randomizing method can be employed to greatly improve the linearity of any type of ADC, but especially flash and successive approximation types. For any ADC the mapping from input voltage to digital output value is not exactly a floor or ceiling function as it should be. Under normal conditions,
3776-415: The time it takes to charge (and/or discharge) its capacitor from 1 ⁄ 3 V supply to 2 ⁄ 3 V supply . By sending this pulse into a microcontroller with an accurate clock, the duration of the pulse can be measured and converted using the capacitor charging equation to produce the value of the unknown resistance or capacitance. Larger resistances and capacitances will take
3840-550: The time to charge the capacitance from a known starting voltage to another known ending voltage through the resistance from a known voltage supply, the value of the unknown resistance or capacitance can be determined using the capacitor charging equation: V capacitor ( t ) = V supply ( 1 − e − t R C ) {\displaystyle V_{\text{capacitor}}(t)=V_{\text{supply}}\left(1-e^{-{\frac {t}{RC}}}\right)} and solving for
3904-411: The unknown input voltage to the input of an integrator and allows the voltage to ramp for a fixed time period (the run-up period). Then a known reference voltage of opposite polarity is applied to the integrator and is allowed to ramp until the integrator output returns to zero (the run-down period). The input voltage is computed as a function of the reference voltage, the constant run-up time period, and
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#17327649758763968-471: The unknown resistance or capacitance using those starting and ending datapoints. This is similar but contrasts to the Wilkinson ADC which measures an unknown voltage with a known resistance and capacitance, by instead measuring an unknown resistance or capacitance with a known voltage. For example, the positive (and/or negative) pulse width from a 555 Timer IC in monostable or astable mode represents
4032-418: The useful resolution of a converter is limited by the signal-to-noise ratio (SNR) and other errors in the overall system expressed as an ENOB. Quantization error is introduced by the quantization inherent in an ideal ADC. It is a rounding error between the analog input voltage to the ADC and the output digitized value. The error is nonlinear and signal-dependent. In an ideal ADC, where the quantization error
4096-433: The whole passband of the converter. If a signal is sampled at a rate much higher than the Nyquist rate and then digitally filtered to limit it to the signal bandwidth produces the following advantages: Oversampling is typically used in audio frequency ADCs where the required sampling rate (typically 44.1 or 48 kHz) is very low compared to the clock speed of typical transistor circuits (>1 MHz). In this case,
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