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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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Analog to Digital Conversion

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Presentation Transcript
  • 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
  • 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 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
  • 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

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

how is it done flash adc
How is it doneFlash ADC

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)