Instrument - signal processor Flashcards
main function of the signal processor (4)
- filter
- detection
- compression
- rejection
filters do what (2)
- gets rid of unnecessary frequencies (rejecting those above/below bandwidth)
- harmonics
benefits of harmonic imaging (4)
- narrow beam (lateral res)
- narrow z plane (elevational res)
- eliminate side/grating lobes
- decrease anterior reverberation/main bang
solution to bandpass filter
pulse inversion
detection AKA
demodulation
purpose of detection/demodulation
converts echo voltages from radio frequency to video/amplitude
two parts to detection
- rectification
2. smoothing
what does rectification do
turns negative voltages into positive voltages
what does smoothing do
levels out differences in amplitude, makes it less bumpy
what is compression? how does it work?
the process of decreasing differences between smallest and largest echo amplitudes to a usable ratio
weaker signals are amplified MORE than stronger ones
dynamic range is done by
compression
what is dynamic range
power ratio of the largest to smallest amplitude that the system can handle
what does 60 dB DR mean
the strongest echo is 10^6 times stronger than the weakest echo
the smallest voltage is 1 mV and the largest voltage is 1000 mV. what is the dynamic range?
voltage ratio = 1000/1 = 10^3
power ratio is (10^3)^2 = 10^6
10^6 in dB is 10+10+10+10+10+10 = 60dB
human vision can only handle ___ dB. what does this mean?
20 dB
for us to view the highest brightness, can only be 100x the lowest
there is more contrast when you ___ DR
decrease DR (fewer shades of gray)
a more smooth image is seen when you ____ DR
increase DR (more shades of gray)
Rejection AKA
signal to noise ratio (SNR)/suppression/threshold
what does rejection do
gets rid of low amplitude echoes/signals - improves SNR (signal to noise ratio)
the signal processor detects doppler shifted echoes using ____ in the _____. what does this determine?
autocorrelation in the quadrature phase detector
autocorrelation determines mean and variance of the the doppler shifted angle at each location along the scan line allowing detection of bidirectional doppler shifts.
