this presentation has been designed for understanding of ADC function, Continuous and Discrete signal, Nyquist criterian for sampling, quantization error and advantage disadvantage of different type of ADC

1. What is ADC ?
Types of ADCs
HC11 & ADC
Analog to Digital Converter
And its type
SHIV DUTT
Lead Engineer
Vedang Radio Technology
Mumbai

2. What is ADC ?
Types of ADCs
Difference
Contents
• What is ADC ?
• Types of ADCs

3. What is ADC ?
What is ADC ?
Types of ADCs
HC11 & ADC
• Definition
• Examples of use
• Conversion process
• Accuracy

4. • Most signals we want to process are analog
• i.e.: they are continuous and can take an
inifinity of values
What is ADC ?
Types of ADCs
HC11 & ADC
Definition
x(t)
t

5. What is ADC ?
Types of ADCs
HC11 & ADC
In the real world every thing is Analog
If you want to measure, Analog is converted into digital and
then again it is converted into Analog.
Light
Pressure
Sound
Temperature
Transducer
Circuit
Display/Mic
rocontroller
Analog Signal Digital Signal
ADC

6. What is ADC ?
Types of ADCs
HC11 & ADC
Measurement and Control Loop

7. What is ADC ?
Types of ADCs
HC11 & ADC
Signal in Time Domain
Amplitude X(t) and time (t)
x(t)
t
Continuous Vs Discrete

8. What is ADC ?
Types of ADCs
HC11 & ADC
Continuous Vs Discrete
∞ 10

9. What is ADC ?
Types of ADCs
HC11 & ADC
Continuous Vs Discrete
Amplitude
Continuous Discrete
Time
ContinuousDiscrete
Analog
Amplitude
Quantized
Sampled
Signal
Digital

10. What is ADC ?
Types of ADCs
HC11 & ADC
Analog to Digital Conversion

11. What is ADC ?
Types of ADCs
HC11 & ADC
Conversion Process
1. Sampler
2. Quantizer

12. What is ADC ?
Types of ADCs
HC11 & ADC
Sampler is a function of Bandwidth

13. What is ADC ?
Types of ADCs
HC11 & ADC
What Nyquist said?

14. xs(t=k*Ts)
• Digital system works with discrete states
• The signal is only defined at determined
times
• The sampling times are proportional to the
sampling period (Ts)
x(t)
Ts
What is ADC ?
Types of ADCs
HC11 & ADC
Conversion process: Sampling
x(t)
tTs
xs(t)

15. What is ADC ?
Types of ADCs
HC11 & ADC
Quantization and error

16. The signal can only take determined values
Belonging to a range of conversion (ΔVr)
• Based on number of bit combinations that
the converter can output
• Number of possible states:
N=2n where n is number of bits
• Resolution: Q= ΔVr/N
What is ADC ?
Types of ADCs
HC11 & ADC
Conversion process: Quantification
t
Ts
xs(t)
ΔVr
Q
xq(t)

17. • Assigning a unique digital word to each
sample
• Matching the digital word to the input signal
What is ADC ?
Types of ADCs
HC11 & ADC
Conversion process: Coding
t
Ts
Q
xq(t)
0
1
2
N-1
N-2

18. What is ADC ?
Types of ADCs
HC11 & ADC
Example
• 8 bits converter: n=8
• Range of conversion: ΔVr=5V
• Sampling time: Ts=1ms
Analog
0
5
0
255
Digital
• Number of possible states: M=28=256
• Resolution: Q=ΔVr/M=19.5 mV
• Analog Filter: ffilter ≈ fs/5 = 200 Hz
f
Gain

19. What is ADC ?
Types of ADCs
HC11 & ADC
Continuous to Discrete Signal

20. Types of ADCs
• Flash ADC
• Sigma-delta ADC
• Dual slope converter
• Successive approximation converter
What is ADC ?
Types of ADCs
HC11 & ADC

21. Comparator is one use
of an Op-Amp
+
-
VIN
VREF
VOUT If Output
VIN > VREF High
VIN < VREF Low
What is ADC ?
Types of ADCs
HC11 & ADC
Flash ADC

22. Advantages
• Very fast
• Simple and easier
to design
Disadvantages
• Needs many parts
(255 comparators
for 8-bit ADC)
• Lower resolution
• Expensive
• Large power
consumption
Flash ADC
What is ADC ?
Types of ADCs
HC11 & ADC

23. • Oversampled input signal goes in the integrator
• Output of integration is compared to GND
• Iterates to produce a serial bitstream
• Output is serial bit stream with # of 1’s proportional
to Vin
What is ADC ?
Types of ADCs
HC11 & ADC
Sigma-Delta ADC
Σ
Integrator

Digital
low-pass
filter
Sample
decimator
Vin +
-
+
1-bit
DAC
-
Oversampler
Serial output

24. Advantages
• High resolution
• No precision
external
components
needed
Disadvantages
• Slow due to
oversampling
What is ADC ?
Types of ADCs
HC11 & ADC
Sigma-Delta ADC

25. • The sampled signal charges a capacitor for a fixed amount of
time
• By integrating over time, noise integrates out of the conversion.
• Then the ADC discharges the capacitor at a fixed rate while a
counter counts the ADC's output bits. A longer discharge time
results in a higher count.
t
Vin
tFIX tmeas
What is ADC ?
Types of ADCs
HC11 & ADC
Dual Slope converter

26. Advantages
• Input signal is
averaged
• Greater noise
immunity than other
ADC types
• High accuracy
Disadvantages
• Slow
• High precision
external components
required to achieve
accuracy
What is ADC ?
Types of ADCs
HC11 & ADC
Dual Slope converter

27. Advantages
• Capable of high
speed
• Medium accuracy
compared to other
ADC types
• Good tradeoff
between speed and
cost
Disadvantages
• Higher resolution
successive
approximation ADCs
will be slower
• Speed limited
~5Msps
What is ADC ?
Types of ADCs
HC11 & ADC
Successive Approximation

28. MAX :
• .1111 1111 = .FF16 = 0.9960937510 = 99.6093 %
Resolution :
• .0000 0001 = .0116 = 0.0039062510 = 0.3906 %
MIN :
• .0000 0000 = 016 = 010=0 %
What is ADC ?
Types of ADCs
HC11 & ADC
Data conversion

29. What is ADC ?
Types of ADCs
HC11 & ADC
Questions ?