Digital Systems Flashcards
Analogue quantities have what kind of values?
Continuous
Digital Quantities have what kind of values?
Discrete
What is an advantage of analogue systems vs digital?
Analogue can handle more power than digital
What is an advantage of digital systems vs analogue?
Digital can process, store and transmit data more efficiently
Give a disadvantage of digital systems
Limited set of values / Not an infinite amount of values, but can store any value
Give an example of a system that uses digital and analogue
CD player; takes in a digital signal from CD and converts it to analogue
Cons of digital systems
Real world is actual analogue
Conversion required
Pros of digital system
Easier to design than analogue
More compact storage
greater accuracy and precision
Operation can be programmed
Less affected by noise
Digital electronics use logic levels that are states of HIGH and LOW. What does a +ve and -ve signal mean in terms of direction?
+ve = signal is going from LOW to HIGH
-ve = signal is going from HIGH to LOW
What are digital waveforms made of?
A series of pulses
What is the difference between an ideal digital signal vs real digital signal
An ideal digital signal will go from one logic level to the next instantly
In reality, digital signals have delays, causing under and overshoots
What is pulse width?
The time between the halfway points on the rising and falling edges of the curve. AKA Full Width at Half Maximum
What is rise time?
The time taken to go from 10% to 90% of signal amplitude
The sampling frequency should be how much of the highest frequency in the signal? And what is it for?
Sampling frequency is at least 2x max frequency of signal. To convert analogue signals to digital.
What is an alias?
A signal that has a frequency Lower than the highest frequency being sampled
. An example is filming a propeller, the frame rate of the camera is too low compared to the RPM of the propeller so it looks like it’s moving backwards
How to counteract Alias?
We use anti aliasing:
- Increase sampling rate
Or
- Cut off all frequencies above the sampling frequency
What is Holding?
A process used to keep the sampling rate constant at least until the next sample is taken (usually one clock pulse)
What is quantisation?
Converting analogue to digital. The sampled frequency is converted to binary, where it is quantised (plotted in a chart, with the analogue wave) and then reconstructed (the digital signals are brought up or lowered to match the analogue curve)
How can me minimize quantization error?
Increases the resolution
Equation for resolution
Resolution = Reference Voltage / (2^number of bits)
E.g. a 4 bit converter has 2^4 states = 16
What is the quantisation error of a 4 bit converter?
1/(2^N)
N = number of bits
1/16
6.25%
Relationship between Quantisation error and resolution?
As resolution increases, quantisation error will decrease as more bits can be read
