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Analog-to-digital converterAnalog-to-digital converter

Prepared by:Prepared by:Selah al-BattahSelah al-Battah

Mohammed Al-khabbazMohammed Al-khabbazAtiyah AlnakhliAtiyah Alnakhli

Ali DumyatiAli Dumyati

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IntroductionIntroduction

--Signals in real world; light, soundSignals in real world; light, sound. .

--When you scan a picture with a scanner what the When you scan a picture with a scanner what the scanner is doing?? (ADC)scanner is doing?? (ADC)It is taking the analog information provided by the It is taking the analog information provided by the

picture (light) and converting into digitalpicture (light) and converting into digital. .

--When you record your voice on your computerWhen you record your voice on your computer,,

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Introduction cont'dIntroduction cont'd

- -Since analog signals can assume any value, noise Since analog signals can assume any value, noise is interpreted as being part of the original signal. is interpreted as being part of the original signal. Digital system, on the other hand, can only Digital system, on the other hand, can only understand two numbers, zero and one. Anything understand two numbers, zero and one. Anything different from this is discardeddifferent from this is discarded..

- -Here we need a translator from analog to digital. Here we need a translator from analog to digital. The devices which play this job are called analog The devices which play this job are called analog

to digital converterto digital converter..

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Analog-to-digital converterAnalog-to-digital converter

--An analog-to-digital converter (abbreviated ADC, An analog-to-digital converter (abbreviated ADC, A/D or A to D)A/D or A to D) is an electronic circuit that converts is an electronic circuit that converts

continuous signals to discrete digital numberscontinuous signals to discrete digital numbers..

--The digital output may be using different coding The digital output may be using different coding schemes, such as binary and two's complement schemes, such as binary and two's complement binary. However, some non-electronic or only binary. However, some non-electronic or only partially electronic devices, such as shaft encoder, partially electronic devices, such as shaft encoder,

can also be considered as ADCscan also be considered as ADCs..

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Techniques of ACDTechniques of ACD

--There are various techniques of A/D There are various techniques of A/D conversionconversion::

11..including flashincluding flash..

22..successive approximationsuccessive approximation..

33..Delta-encodedDelta-encoded..

44..IntegratorIntegrator..

55..delta sigma or modulatordelta sigma or modulator..

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A direct conversion ADC or flash ADCA direct conversion ADC or flash ADC

-A direct conversion is very fast, but usually has -A direct conversion is very fast, but usually has only 8 bits of resolution (256 comparators) or only 8 bits of resolution (256 comparators) or fewer, as it needs a large, expensive circuit. ADCs fewer, as it needs a large, expensive circuit. ADCs of this type have a large die size, a high input of this type have a large die size, a high input capacitance, and are prone to produce mistakes capacitance, and are prone to produce mistakes on the output (by outputting an out-of-sequence on the output (by outputting an out-of-sequence code). code).

--example:example: They are often used for video or other fast signals. They are often used for video or other fast signals.

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A successive approximation ADCA successive approximation ADC

This type uses a comparator to reject ranges of This type uses a comparator to reject ranges of voltages, eventually settling on a final voltage range. voltages, eventually settling on a final voltage range. The way successive approximation works is through The way successive approximation works is through constantly comparing the input voltage to a known constantly comparing the input voltage to a known reference voltage until the best approximation is reference voltage until the best approximation is achieved. At each step in this process, a binary achieved. At each step in this process, a binary value of the approximation is stored in a successive value of the approximation is stored in a successive approximation register (SAR). the SAR uses a approximation register (SAR). the SAR uses a refernce voltage for conversionrefernce voltage for conversion..

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A A delta-encoded ADCdelta-encoded ADC

- A delta-encoded ADC has an up-down - A delta-encoded ADC has an up-down countercounter that feeds that feeds a (DAC). The input signal and the DAC both go to a a (DAC). The input signal and the DAC both go to a comparator. The comparator controls the counter. The comparator. The comparator controls the counter. The circuit uses negative circuit uses negative feedbackfeedback from the comparator to from the comparator to adjust the counter until the DAC's output is close enough adjust the counter until the DAC's output is close enough to the input signal. The number is read from the counter. to the input signal. The number is read from the counter.

- Delta converters have very wide ranges, and high Delta converters have very wide ranges, and high resolution , but the conversion time is dependent on the resolution , but the conversion time is dependent on the input signal level.input signal level.

- Delta converters are often very good choices to read Delta converters are often very good choices to read real-world signals..real-world signals..

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IntegratorIntegrator An integrator An integrator ADCADC (also called (also called ramp-compareramp-compare , , dual-dual-

slopeslope or or multi-slopemulti-slope ADC) produces a ADC) produces a saw-tooth signalsaw-tooth signal that ramps up, then quickly falls to zero. When the ramp that ramps up, then quickly falls to zero. When the ramp starts, a timer starts counting. When the ramp voltage starts, a timer starts counting. When the ramp voltage matches the input, a comparator fires, and the timer's value matches the input, a comparator fires, and the timer's value is recorded. Timed ramp converters require the least is recorded. Timed ramp converters require the least number of number of transistorstransistors..

- The ramp time is sensitive to temperature??- The ramp time is sensitive to temperature?? There are two solutions: use a clocked counter driving a There are two solutions: use a clocked counter driving a

DACDAC and then use the comparator to preserve the and then use the comparator to preserve the counter's value, or calibrate the timed ramp.counter's value, or calibrate the timed ramp.

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A A Sigma-Delta ADCSigma-Delta ADC - Also known as a Delta-Sigma ADC over samples the - Also known as a Delta-Sigma ADC over samples the

desired signal by a large factor and filters the desired desired signal by a large factor and filters the desired signal band. Generally a smaller number of bits than signal band. Generally a smaller number of bits than required are converted using a Flash ADC after the Filter. required are converted using a Flash ADC after the Filter. The resulting signal, along with the error generated by the The resulting signal, along with the error generated by the discrete levels of the Flash, is fed back and subtracted discrete levels of the Flash, is fed back and subtracted from the input to the filter. This negative feedback has the from the input to the filter. This negative feedback has the effect of effect of noise shapingnoise shaping the error due to the Flash so that it the error due to the Flash so that it does not appear in the desired signal frequencies. A digital does not appear in the desired signal frequencies. A digital filter follows the ADC which reduces the sampling rate, filter follows the ADC which reduces the sampling rate,

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ResolutionResolution

--The resolution of the converter indicates the number of The resolution of the converter indicates the number of discrete values it can produce over the range of voltage discrete values it can produce over the range of voltage values. It is usually expressed in (bits). For example, an values. It is usually expressed in (bits). For example, an ADC that encodes an analog input to one of 256 discrete ADC that encodes an analog input to one of 256 discrete values (0...255) has a resolution of eight bits, since 2^8 = values (0...255) has a resolution of eight bits, since 2^8 = 256256..

--Resolution can also be defined electrically, and expressed in Resolution can also be defined electrically, and expressed in volt. The voltage resolution of an ADC is equal to its overall volt. The voltage resolution of an ADC is equal to its overall voltage measurement range divided by the number of voltage measurement range divided by the number of

discrete valuesdiscrete values..

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Commercial analog-to-digital convertersCommercial analog-to-digital converters

- -These are usually integrated circuitThese are usually integrated circuit..

- -Most converters sample with 6 to 24 bits of resolution, and Most converters sample with 6 to 24 bits of resolution, and produce less than 1 mega sample per second. It is rare to produce less than 1 mega sample per second. It is rare to get more than 24 bits of resolution. Mega sample get more than 24 bits of resolution. Mega sample converters are required in digital video cameras, video converters are required in digital video cameras, video capture card, and TV tuner card to convert full-speed capture card, and TV tuner card to convert full-speed analog video to MPEG digital video filesanalog video to MPEG digital video files..

- -Commercial converters usually have ±0.5 to ±1.5 LSB error Commercial converters usually have ±0.5 to ±1.5 LSB error

in their outputin their output..

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Application to music recordingApplication to music recording

- ADCs are integral to much current music ADCs are integral to much current music reproduction technology, since much music reproduction technology, since much music production is done on computers; even when production is done on computers; even when analog recording is used.analog recording is used.

- An ADC is still needed to create the PCM data An ADC is still needed to create the PCM data stream that goes onto a compact discstream that goes onto a compact disc..

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Other applicationsOther applications

- AD converters are used virtually everywhere where an AD converters are used virtually everywhere where an analog signal has to be processed, stored, or transported analog signal has to be processed, stored, or transported in digital form. Fast video ADCs are used, for example, in in digital form. Fast video ADCs are used, for example, in TV tuner cards. Slow on-chip 8, 10, 12, or 16 bit ADCs are TV tuner cards. Slow on-chip 8, 10, 12, or 16 bit ADCs are common in microcontrollers.common in microcontrollers.

- Very fast ADCs are needed in digital oscilloscopes, and are Very fast ADCs are needed in digital oscilloscopes, and are crucial for new applications like software defined radiocrucial for new applications like software defined radio

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QuestionsQuestions????