1 - 3 (2nd) Flashcards
What is a signal?
something which carries Information
Depending on signals’ temporal recurrence, signals can be ___, ___ and ___ (3 characteristics)
Periodic
Quasiperiodic (almost periodic)
Stochastic
Medical signal processing chain
Before the signals enter amplifier, which device does it need to go through first?
Transducers
An example of quasiperiodic signal. Why is it almost periodic?
ECG signals
=> looks periodic over a short time period (few sec), but the change of rhythm of the heartbeat is not precisely periodic (b/c of healthy day-cycle or pathological reasons during hours or days…)
ECG (signals)
Information?
Original?
Encoding needed? Why?
Info - heart cycle
O - voltage across points
E - no, but filtering is required to remove unwanted portion
Heartbeat (signals)
Info - Heart cycle parameters, anatomical and flow problems.
Original?
Encoding needed?
Origin - Acoustic waves (sound)
E - electrical signal from the microphone -> Coloured image on the computer screen
(frequency spectrum)
Entirely periodic biological signals are rare but carry lots of information.
TRUE OR FALSE?
False
=> they carry very little info
An example of stochastic signals.
=> Why are they stochastic?
Gamma photons detected during an isotope diagnostics (e.g, PET-SCAN,…..)
=> You can only give probability distribution between of the time that passes between arrival of 2 photons
(=> the info in this case is photon number detected during a longer time period)
Signals in medicine
PET: Positron Emission Tomography
Information?
Original?
Encoding needed?
Info - Location of drug, labeling molecule, etc.
Origin - gamma photons
E - electrical pulses from the detector.
-> Coloured image on the computer screen
SPET-CT:Single Photon Emission Computed Tomography
Information?
Original?
Encoding needed?
Info - Anatomy (X-ray) Label (desease,etc)
O - gamma photons, X-ray photons
Encoding - electrical pulses From the detector -> colored image
Signals in medicine
Heart beat
Information - Blood composition
Original?
Encoding needed?
O - Cell types and count in unit volume
E - electrical signal from the cell sorter => areas under the histogram
On the bass of possible changes in the physical quantity of signals
=> What are the 2 types of signals can be seen?
Analogue and digital signals
The basic characteristics of analogue and digital signals is that ____
only certain ranges of values (usually voltage ranges) are allowed
List 5 signal shapes
Periodic
Quasiperiodic
Stochastic
Continuous
Pulse
The basic characteristics of analogue and digital signals is that only certain ranges of values (usually voltage ranges) are allowed.
=> These ranges are separated by ____
Forbidden intervals (where the interpret ion is indefinite)
Due to forbidden voltage ranges, digital signals are quite _____ to disturbances
insensitive
(this is why CD-recording is still good as original one after many duplications)
Analogue signals are either ____ or ____ signals (2 adjs)
continuous
pulse
What is a pulse signal?
The signal that has information supplied by occasional rapid changes of a physical quantity followed by a rapid return to the original value
Give each example for electric and non-electric pulse signals
Electric- scintillation counter
Non-e - hiccups and coughing
Fourier theorem states that:
any signal can be decomposed as a sum of sinusoidal signals, and any signal can be constructed from sinusoidal components.
Why is Fourier theorem useful in signal processing?
This is useful in signal processing because if the frequency range of the measured signal is known, the signal processing system only has to transfer sinusoidal signals of this frequency range, and thus it can reconstruct the signal without distortion.
Fourier theorem
In the case of periodic signals, the frequency of sinusoidal are the ____
Integral multiplies of the frequency of signal
Fourier theorem
To reproduce the desired signal shape as a sum of sinusoidal signals, the _____ have to be chosen appropriately
he amplitudes of the sine function
Fourier theorem
Why doesn’t the processing device have to be investigated with respect to all kind if signals
=> Due to Fourier decomposition, the investigation of sinusoidal signals is enough
What happen if the characteristics frequency range of the signal to be processed is known
If the characteristics frequency range of the signal to be processed is known
=> the signal-processing system only has to transfer w/o distortion sinusoidal signals belonging to this frequency range to preserve the shape of the signal
Fourier analysis of periodic signals
The Fourier transform of a periodic function consists of a series of equally spaced impulses and these impulse are located at the harmonic frequencies of the signal.
Fourier analysis of non-periodic signals
The assumption of the Fourier transform is that all signals can be expressed as a sum of periodic (specifically sinusoidal) components with varying amplitude and phase.
-> If the non-periodic signal is defined over a finite time span, it can be considered to be one part of a periodic signal
(We can have many pictures of the same Time-based (more convetional)
or
Frequency-based
(useful,but a bit abstract))
What is the most important property of an amplifier?
Its voltage and power amplification
Voltage applied to the input of the amplifier gives rise to a ___ on the input
current
Voltage applied to the input of the amplifier gives rise to a current on the input
=> The input behaves as a ______, ____ of which can be determined from the ratio of the voltage and the current on the input
=> this is called input resistance
Resistor
Resistance
Voltage applied to the input of the amplifier gives rise to a current on the input
=> The input behaves as a resistor, resistance of which can be determined from the ratio of the _____ and the _____ on the input
=> this is called input resistance
voltage
current
Voltage applied to the input of the amplifier gives rise to a current on the input
=> The input behaves as a resistor, resistance of which can be determined from the ratio of the voltage and the current on the input
=> this is called ___
input resistance
What is input resistance?
The resistance seen by an AC source connected to the amplifier input
(look at R in and R out on diagram)
The power amplification is the ratio of ____
two powers (in and out)
The amplification of the negative feed back is always ___ than the original.
This holds for any ____
smaller
frequency
How is the power amplification is usually plotted?
the power amplification in decibels (n) is usually plotted against the logarithm of the frequency
(a double logarithmic plot -> the amplification in decibels is proportional to logarithm of the power amplification)
If the transfer function is linear, then the shape of the (1)_____ (2w) is (2)_____ to the (3)______ and (4) _____ of distortions.
(1) Output signal
(2) similar
(3) output
(4) free
Variations of the input voltage Uin result in modulation of resistance R1 of the transistor.
=> This change can be very (1)____, which allows control of the (2)_____ even in the case of rapidly changing (3)_____ signals.
Unfortunately, the (*)______ of the transistor are (4)______ (remember, in the case of the voltage divider it was (5)______),
=> the signal shape of the output Uout = U1 is (6)______ compared to the input.
(1) fast
(2) Output
(3) input
(*) transfer characteristics
(4) nonlinear
(5) linear
(6) distorted
Why is feedback loop is a linear circuit element?
A voltage divider circuit is used as the feedback loop, which is built
from resistors
The frequency range (between the flower and fupper cut-off frequencies), where the gain is roughly (1)_____ is called (2)_____
By convention, the frequency values at the max. gain level is (3)____ gain values are the (4)____ and the (5)______ (6)______ flower and fupper, respectively.
Here, nmax means the (7)_____ gain level of the (8)_______, and the gain level (9)______ lower means that the power of the output signal (10)______
(1) constant
(2) transfer band
(3) -3dB
(4) Lower
(5) Upper
(6) Cut-off frequencies
(7) highest
(8) transfer band
(9) 3 dB
(10) decreases by half
The role of analogue-digital (A/D) converters
Convert analogue signals to digital signals
What are the 3 important parameters for analogue-digital (A/D) converters?
(1) The range of the input voltage it can convert
(2) Resolution of converter
(i. e the number of digital voltages needed to display output digital signal. bla bla)
(3) Frequency of sampling (should be high enough)
Characteristics of digital signals
discrete in time and in value
How to restore analog signals?
By using Digital to analog converter (DAC)
A/D conversion (ADC)
How is sampling happen for digital signals?
Sampling of sine waves
=> For non-sine signals: „first apply Fourier, then sample each sine”
Nyquist theorem
For successful reconstruction of the signal, the frequency of the sampling should be at least twicehigher than the highest frequency signal component (overtone)
( It is the principle to accurately reproduce a pure sine wave measurement, or sample, rate, which must be at least twice its frequency.)
Which type of signal going through ADC?
Unfiltered analog signal
Which type of signal going out of ADC?
Which device will it go in?
Sample digitized signal
Processor
Which type of signal going out of processor?
Which device will it go in?
Digitally filtered signal
DAC
Which type of signal going out of DAC? (NOT ADC)
Filtered analog signal
What is Gain Bandwidth Product?
Gain · Bandwidth = constant
-> represents the amount of frequencies or the band of frequencies that the amplifier is most effective in amplifying.
The available power to the amplifier can either be put to use as:
high signal gain over a limited bandwidth or limited gain over a wide bandwidth.
Frequency range of the signal must ___ the bandwidth!
match
Processing of pulse signals.
Integral discrimination: selecting signals higher than a certain amplitude. Used when filtering out noise for example in scintillation counter.
Differential discrimination: selecting signals within a defined range. For example, used when counting according to size distribution (coulter counter)
Digitization of analog signals.
Analog signals need to be converted to digital signals so that they can be read and interpreted.
→ ADC is the device which can make this conversion. It is done by performing many readings of voltage at different times, assigning values to them (i.e sample readings).
→ The more sample readings, the more precisely it converts the original signal.
→ The sample reading should take place at the same frequency as the signal, so that it doesn’t miss anything.
Parts and function of filter circuits.
function: remove unwanted frequencies from the signal.
parts: resistor and capacitor (dependant to frequency)
Transporting and processing signals in medicine
We need to separate information from noise!
What is Analog signal?
Analog signal is a continuous signal which represents physical measurements
