1. Fri. Oct 13 Announcements Lab practical next week
Review session Monday – materials posted
Survey going around: You will be given 5 mins at the end of class to fill it out and hand it into the box up front
Please anonymous (I want to know what you really think)
As part of the survey, I also want you to write down
One thing you learned today
One question you have from today’s material (or the class in general)

2. Analog-to-Digital Converter
Module 3.B
Analog-to-Digital Converter
Tim Rogers 2017

3. Learning Outcome #3 A: Clocks and Real Time Interrupt (RTI)
“An ability to effectively utilize the wide variety of peripherals integrated into a contemporary microcontroller”
A: Clocks and Real Time Interrupt (RTI)
B: Analog-to-Digital Converter (ATD)
C: Serial Peripheral Interface (SPI)
D: Timer Module (TIM)
E: Pulse Width Modulation (PWM)
F: Serial Communications Interface (SCI)
How?

4. Learning Outcome #3 Why? “Analog to digital conversion”
The digital world is quantized and has fixed information size
On a macro scale, the real world is continuous and analog.
ATD

5. Analog Conversion Basics
If your reference voltages are 0V and 5V, and you have 2 bits to encode each sample, then the sampled voltage values possible are:
(A) 0, 2.5V
(B) 0V, 1.25V, 2.5V, 3.75V, 5V
(C) 0V, 1.25V, 2.5V, 3.75V
(D) 1.25V, 2.5V, 3.75V, 5V
(E) 0, 2.5V, 5V
Analog Conversion Basics
Rate at which you take samples is called the sampling rate
Each reading of the analog signal is a sample
Each sample has a finite number of bits: quantization
Values always relative to a reference voltage. What you store is a fraction of the reference voltage.

6. Analog Conversion Basics
Design space for ATD converters involves picking the:
sample rate
# bits for quantization
encoder type
Analog Conversion Basics
Rate at which you take samples is called the sampling rate
Each reading of the analog signal is a sample
Goal: Reproduce the analog signal as faithfully as possible given constraints and acceptable error
Each sample has a finite number of bits: quantization
Actually reading the sample to find most appropriate value is called encoding
Values always relative to a reference voltage. What you store is a fraction of the reference voltage.

7. Determining an individual value (sampling)
One way to help narrow this sampling time is to use a “sample-and-hold” (S/H) circuit that acts as an ”analog memory”
S/H circuit will read in a voltage, then hold that value while the converter makes it binary
But in reality, converting the value to a digital value is not infinitely fast
Ideally, when we read in a voltage we do it infinitely fast

8. Setting the Sampling rate
If the highest frequency component of the input signal is Fi, what must your sampling frequency (Fs) be to ensure correct conversion?
(A) Fs=Fi
(B) Fs=Fi/2
(C) Fs=Fi*2
(D) Fs=Fi*4
(E) Fs=Fi/4
Key component of setting up an ATD is setting the sampling rate Ts
To do this – you need to do a spectral analysis of your input signal.
If the input signal has higher frequency components than Fs/2, you need to put a low-pass filter on the ATD input

9. If Fs (sampling frequency) = 20kHz an 11 kHz input signal (without any filtering) be encoded as:
(A) 10 kHz
(B) 11 kHz
(C) 9 kHz
(D) 21 kHz
(E) None of the above
ATD Filtering
Q: What happens if you do not filter out the high frequency components?
A: Aliasing!
Original waveform
Alias reconstruction
In the frequency domain
Filter on ATD input referred to as anti-aliasing filter
Without a filter, frequencies are “folded back” into the baseband

10. Quantization
Number of bits for each sample: often called dynamic range
Quantization is the assignment of a fixed amplitude level (corresponding to an available binary code) to the incoming analog signal
Note that the converted code is relative to the reference voltage(s) applied to the converter (VRH = voltage reference high, VRL = voltage reference low)

11. Illustration of Quantization

12. Quantizing Intervals and Quantization Error
X Vrh
X Vrh

13. Quantizing Intervals and Quantization Error

14. Quantizing Intervals and Quantization Error

15. Quantizing Intervals and Quantization Error

16. Quantizing Intervals and Quantization Error

17. Quantizing Intervals and Quantization Error

18. Quantizing Intervals and Quantization Error

19. Quantizing Intervals and Quantization Error

20. Quantizing Intervals and Quantization Error

21. Quantizing Intervals and Quantization Error

22. Quantizing Intervals and Quantization Error

23. Quantizing Intervals and Quantization Error

24. Quantizing Intervals and Quantization Error

25. Quantizing Intervals and Quantization Error

26. Quantizing Intervals and Quantization Error

27. Quantizing Intervals and Quantization Error

28. Quantizing Intervals and Quantization Error

29. Quantizing Intervals and Quantization Error

30. Reminder: Block Manual for 9S12 ATD