Post by misterc on Mar 27, 2023 10:48:42 GMT
Good Morning students,
I know its' a Monday & the weekend may not have given you the oppotunities you were looking by accquiring a win on the lottery or bagging a 28 Y.O. nubile wealthy attractive, intelligent, unpurchased, NON air head lady friend.
Title for today's new topic:
Impedende matching 101
Serial data signal integrity lets us begin with time domain reflectometry
Some early light reading for you to study before we begin todays proceedings
Impedence matching Professional 2
Or in laymans terms one method of seeing the effects of impedence mismatches in cabling, connectors, both board fixed, cable terminated and circuit board deviations.
Please observe a true impedence matched 50 Ohm transmission line (By this we mean fully matched all the way the signal pathway) the second image also displays a zoom trace of the top transitiong edge of the wave form, now we are using a 12 bit technology so the resolution compared to most scops is 16 times greater so therefore we we have crisp, clean easily visable wave forms. Also note a signifcant number of samples were taken on each screen image.
The scope was optimised for maximum performnace by using the maximum amount of ADC performnace but having the wave form fill the majority of the screen, sample rate was 10GS/s The measurment parameters are easily visiable for comparsions.
Next two images are of the same set up, this time using a high quality 75Ohm cable, you can 'see' the results of the signal being bounced (reflected) back and forth in the cable at the transisitioning of the rise edge to waveform dwell time and conversely on the falling edge to the negative dwell period with a zoom trace below this as well
Thses next two images are of the same 50 0hm transmitter (clock) 75 Ohm cable and a quality impedence matching device (Scope deskew probe head in this case) Again while a very positive step back towards the 'ideal' impedence matched pathway its still not quite right BUT its far superior to having the second set of images both in terms of waveform desribility & SQ