Waves Digitising analogue data. Analogue What we see in the real world around us Continuously...
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![Page 1: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/1.jpg)
Waves
Digitising analogue data
![Page 2: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/2.jpg)
Analogue
• What we see in the real world around us
• Continuously varying– Temperature– Land contours– Speed– Time
Tem
p
Time
![Page 3: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/3.jpg)
But how do we make measurements
• We cannot record measurements continuously (too much storage)
• Once every second? Minute? Millisecond?
Tem
p
Time
![Page 4: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/4.jpg)
And we record with a certain granularity too
• 15oC• 15.4oC• 15.358oC• 15.358374864826535243oC• So we have compromised on both axes – we can’t
be sure of the temperature at all between the measuring points, and we don’t know the exact temperature at any moment anyway
![Page 5: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/5.jpg)
This is what we have to do to digitise data
• We lose information – inevitably
• Analogue data is continuous– Digital data has a discrete set of values
• But there are big advantages– Computers can handle the data when digitised– It allows us to store, process and transmit the
data more easily
![Page 6: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/6.jpg)
Just 1s and 0s
• Analog to Digital Convertor (ADC)– Converts wave form to binary – Samples at known rate– Known resolution
• Say waveform 0 ≤ V ≤ 10 at 8 bits
• Step = 10 /256 = .039v per step
![Page 7: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/7.jpg)
Logic levels
• Problem: A voltage on a wire is actually an analogue signal! It is continuously varying.
• HIGH may be interpreted as (e.g.) any time the voltage is between 2V and 5V
• LOW may be any time it is between 0V and 0.8V
VH(max)
VH(min)
VL(max)
VL(min)
HIGH (Binary 1)
Uncertain
LOW (Binary 0)
![Page 8: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/8.jpg)
Digital waveforms
• A pulse is generated when a signal goes from LOW to HIGH, and back again (+ve pulse)
• A pulse has a rising edge, and a falling edge
Rising (leading) edge
Falling (trailing) edge
Rising (trailing) edge
Falling (leading) edge
Negative-going pulsePositive-going pulse
![Page 9: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/9.jpg)
Not so simple
• The figures on the last slide are ideal – instantaneous change between HIGH and LOW
• But reality is not like that– The waves take time to transition from HIGH
to LOW
![Page 10: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/10.jpg)
A digital wave
90%
10%
tr tf
50%tw
Pulse width
Voltage (pulse)
amplitude
![Page 11: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/11.jpg)
Overshoot and ringing
These effects are caused by capacitance and inductance in the circuit
![Page 12: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/12.jpg)
Waveform Characteristics
• Most waveforms encountered are composed of a series of pulses, sometimes called pulse trains, and can be classified as either periodic or nonperiodic.
• A periodic pulse train pulses at a fixed interval, called a period (T). The frequency (f) is the rate at which it beats (pulses) itself and is measured in hertz (Hz).
• The frequency (f) of a pulse waveform is the reciprocal of the period, f = 1/T
![Page 13: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/13.jpg)
Periodic
Nonperiodic
![Page 14: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/14.jpg)
Duty Cycle
• An important characteristic of a periodic waveform is its duty cycle. This is defined as the ratio of the pulse width (tw) to the period (T) expressed as a percentage, – Duty cycle = (tw/T) × 100% tw
T
Exercise: for the diagram, work out the:
a) periodb) frequencyc) duty cycle 0 1 3 t (ms)
![Page 15: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/15.jpg)
Many digital systems are synchronised with a waveform called the clock
The Clock
This is a periodic waveform in which each interval between pulses (the period) equals one bit time
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Timing diagrams
You’ll often see diagrams like this, showing the time relationship between waveforms
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The Integrated Circuit• Used almost exclusively
• Low power consumption
• Small
• Reliable
• Cheap
![Page 18: Waves Digitising analogue data. Analogue What we see in the real world around us Continuously varying –Temperature –Land contours –Speed –Time Temp Time.](https://reader038.fdocuments.us/reader038/viewer/2022110213/56649ec95503460f94bd71a1/html5/thumbnails/18.jpg)
ICs• One single piece of silicon
• All the components – transistors, diodes, resistors and capacitors – are an integral part of that chip
• Various types of package exist
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Pin numbering
All IC packages have a standard format for numbering the pins (leads).
Pin 1 is always identified by either a small dot or a notch or a bevelled edge. Starting with pin 1, the numbering is always anti-clockwise as viewed looking down upon the package