Semester 1 Flashcards
What does a CPU do?
Central Processing Unit
Executes instructions, performs calculations, controls input and output
What does main memory do?
Short term memory directly accessible to CPU. Programs run from here, data being used stored here
What does a hard drive do?
Long term storage of data or programs not currently being used
What is an analogue quantity?
A continuously varying quantity
What is a digital quantity?
A quantity defined as a serries of discrete values
What signals do computers require?
Signals that are digital: discrete in amplitude and time
How are digital signals represented?
In binary
What determines the range of measurement in digital signals?
Reference voltage Vᵣ
How do you calculate a discrete, digital value for an analogue measured value V(t)?
x =|V(t) * 2ᴺ / vᵣ |
vᵣ is reference voltage
N is the number of bits
|| is the floor(truncation) operator
How do you calculate the resolution of a digitized singal?
vᵣ / 2ᴺ
How is the sampling frequency and the time separating each sample related?
fₛ is sampling frequency
Δt = 1 / fₛ
Why must the sampling frequency must be much higher than the frequency you want to measure?
Because if fₛ ≤ f, then aliasing occurs
Usually use fₛ > 10f
Define accuracy
Closeness of measurements to actual value
Define precision
Consistency of the measurement
Define resolution
Smallest measurable change
What does noise affect from accuracy, precision and resolution?
precision and resolution
not accuracy!
Define noise.
Random fluctuation of electrical signal unrelated to what is being measured, equivalent to having a random error in each measurement.
How should we treat the measurement voltage V(t) in relation to the signal and noise?
As a superposition / sum
V(t) = Vₛ(t) + Vₙ(t)
What are the two ways of quantifying noise?
- Root mean square amplitude Vrms
- Signal to noise ratio SNR
How do you calculate Vrms?
sqrt( 1/T 0->T∫V²(t).dt )
How do you calculate the SNR?
Average Signal power / average noise power
Pₛ /Pₙ
Vₛ² / Vₙ²
How do you convert SNR to decibels
SNR(dB) = 10 log₁₀ (SNR)
What does amplification do?
- Increases amplitude total electrical signal (including noise) by gain, G.
- Reduces SNR by noise factor of amplifier
- Improves resolution by matching output to range of system
What is averaging?
Repeating the same measurement and finding the average response
How does the average noise be calculated after averaging?
V ₐᵥₑ = Vₙ / sqrt(M)
where M is the number of measurements
How can you find the SNR of an averaged system?
SNR(ave) = M x SNR
M is the number of measurements
