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Analog to Digital Conversion. Introduction. An analog-to-digital converter ( ADC , A/D , or A to D ) is a device that converts continuous signals to discrete digital numbers

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Presentation Transcript
introduction
Introduction
  • An analog-to-digital converter(ADC, A/D, or A to D) is a device that converts continuous signals to discrete digital numbers
  • In electronics, a digital-to-analog converter(DAC or D-to-A) is a device for converting a digital (usually binary) code to an analog signal (current, voltage or charges). Digital-to-Analog Converters are the interface between the abstract digital world and the analog real life. Simple switches, a network of resistors, current sources or capacitors may implement this conversion
important terminologies in adc
Important terminologies in ADC
  • Resolution
  • Response type
    • Linear ADCs
    • Non-linear ADCs
  • Accuracy
  • Sampling rate
  • Aliasing
resolution
Resolution
  • The resolution of the converter indicates the smallest analog value that it can convert to a digital number
  • If the ADC has 8 bits and the Full scale is 0-5 Volts, then the ADC voltage resolution is:
    • 5/28 = 0.01953125 Volts
response type
Response type
  • Linear ADCs
    • Output binary value changes approximately with the analog value within the resolution (or ½ the resolution)
  • Non-linear ADCs
    • Uses techniques known as companding to ‘magnify” the low amplitude analog signals
      • m-law
      • A-law
      • Dolby
accuracy
Accuracy
  • Accuracy depends on
    • Quantization error
    • Non-linear error caused by the physical imperfections of ADC
sampling rate
Sampling rate
  • For ADC, a signal values are measured and stored at intervals of time Ts, the sampling time.
  • A bandlimited analog signal must be sampled at a frequency fs = 1/Ts that is twice the maximum frequency (fa) of the bandlimited signal
  • fs = 2fa is known as the Nyquist Sampling frequency
aliasing
Aliasing
  • If a signal values are measured and stored at frequencies greater than the Nyquist sampling rate, the signal can be reproduced exactly (within quantization and other non-linear error accuracy).
  • However, If a function is sampled at less than Nyquist rate, the resulting function may have different frequency content. This is known as aliasing.
    • For example: If a 3 KHz sine wave is sampled at 4 KHz, the resulting signal will appear as a 1 KHz signal.
how is it done digital ramp adc
How is it doneDigital-Ramp ADC

http://hyperphysics.phy-astr.gsu.edu/HBASE/Electronic/adc.html

how is it done successive approximation adc
How is it doneSuccessive Approximation ADC

http://hyperphysics.phy-astr.gsu.edu/HBASE/Electronic/adc.html

how is it done flash adc
How is it doneFlash ADC

http://hyperphysics.phy-astr.gsu.edu/HBASE/Electronic/adc.html

analog to digital chip adc0820
Analog to Digital chip: ADC0820
  • 8-Bit High Speed µP Compatible A/D Converter with Track/Hold Function
  • Uses ½ flash conversion technique
    • consists of 32 comparators
    • a most significant 4-bit ADC
    • a least significant 4-bit ADC
  • 1.5 µs conversion time
  • Does not need external sample-and-hold for signals moving at less than 100 mV/µs.
analog to digital chip adc082014
Analog to Digital chip: ADC0820
  • Has many input modes, RD, WR-RD, WR-RD Standalone
  • Input pulse required to read analog data (Sample)
    • Must sample at more than Nyquist rate (fs = 2*fa)
  • Outputs signal when data is valid
adc0820 wd rd mode
ADC0820 – WD-RD Mode

t1 = tINTL= 800 ns

adc0820 wd rd mode17
ADC0820 – WD-RD Mode

t1 = tINTL= 800 ns

acquiring an analog signal
Acquiring an Analog Signal
  • Input is a sinusoidal signal with peak to peak of 5 V
  • Voltage input in the range -2.5 to 2.5 V
  • Use Analog to Digital Converter ADC0820
    • Input’s analog voltage 0 to 5 V
    • Requires adding 2.5 Volts to input signal before converted.
op amp non inverting adder
Op-Amp - Non-Inverting Adder
  • Use LM741 Operational Amplifier
  • Eqs: Vo =V1 + v2 (for all resistors equal)

Vo = (R1+R2)/R2 (V1 R4 + V2R3)/ (R3+R4)

references
References
  • http://en.wikipedia.org/wiki/Analog_to_digital_converter
  • http://hyperphysics.phy-astr.gsu.edu/HBASE/Electronic/adc.html
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