Signal classifications Flashcards
first important classification betwwen 2 types of signals
analog and digital
what is an analog signal
a continuous time function
what is a digital signal
a signal given at discrete times (after A/D conversion)
advantages of digital systems
-no sensitivity to electro-magnetic interference
-low uncertanty at relatevely low cost
-high repeatability and reproducibility
-easy to manipulate, transmit and reproduce
-flexible
-fast
-only way to store info in computer
-more robust to noise
drawbacks of digital systems
we loose information and we aproximate information, if we use a small sampling time we don’t loose important info, if distance between horizontal lines is correct also the approximation doesn’t let us loose important info
what is a logical signal
is the easiest kind of codification, it has just 2 discrete states: on and off.
(their origin can be both a digital or analog signal)
which are the 2 main types of logical signal
trigger signal and TTL (Transistor to Transistor Logic)
example of logical signal
signal of photocells, 0 if there is nothing in front of it 1 if there is something
other important 2 categories of signal classification
deterministic and random
deterministic has 2 sub categories which are
periodic and non periodic
deterministic periodic signal has 2 sub categories which are
simple harmonic and complex harmonic
deterministic non periodic signal has 2 sub categories which are
quasi periodic and transient
random has 2 sub categories which are
stationary and non stationary
random stationary has 2 sub categories which are
ergodic and non ergodic
def of random signal
if we know the value of the signal at time t it’s not possible to forsee the value the same signal will have at the immediately next time (t+dt) or at the far future
def of periodic signal
signal given in the time domain as function whose shape repeats itself at defined time lags all equal to each other
example of single harmonic periodic deterministic signal
shaft vibration due to residual unbalance
what is a deterministic, periodic, complex harmonic signal
is the sum of many harmonic components, it can be decomposed in a fourier series
what is a deterministic, non periodic, quasi-periodic signal
in general a signal made from the sum of many harmonic components is not periodic, it is periodic only if the ratio between any frequency related to different harmonic components is a rational number, so only a foundamental frequency Tp exists.
a signal is quasi periodic if at least 1 component is not an integer multiple of this foundamental frequency
how is the fourier spectrum of a quasi periodic signal
it’s discrete (energy concentrated at given frequency values), it’s similar to that of complex periodic signal
how is the spectrum of a deterministic, non periodic, transient signal
cannot be discrete, just continuous
def of random non stationary signal
a random process is non stationary if the mean value and the auto correlation function vary with time
def of random weakly stationary signal
a random process is weakly stationary if the mean value and the correlation functiondo not vary with time.
this means the mean value is constant and the correlation is just function of the delay tau
def of random stationary signal
a signal is stationary if the infinite higher order moments and the join moments are independent of time
