Lab X - ECE 421L 

Authored by Worku, Yetneberk

E-mail: workuy@unlv.nevada.edu

Today's date  02/08/14

Lab description and Discussions of Scope probe

A. Scope waveforms of 10:1 probe  are undercomensated, overcompensated, and compensated; showing consequently as the following. 

TEK00003.fw.pngTEK00004.fw.pngTEK00001.fw.png

1. showing on LTspice simulation of a 10:1 scope probe with no scope
noscope.JPG
 a. using hand calculations
Capture.JPGCapture1.JPG
2. showing LTspice of a simulation of 10:1 probe with overcompansated
Capture2.JPG
3. showing LTspice simulation of a 10:1 probe with undercompansated
Capture3.JPG
4. showing LTspice simulation of a 10:1 probe with compansated
Capture4.JPG
B. This is the draft schematic of a 10:1 scope probe
Capture1.PNG
C. Finally, compansated, undercompansted, or overcompansted will happen by changing the Capacitance values, or by switching the  probe tip has switch, for example need to set the scope input to be 0.1 of the test point, then turn to 10x side. Also, use circuit analysis and make some assumptions; the hand calculations show as follows.
Capture5.JPG
Experiments by using Comensated scope probe
1. The first experiments using a scope, pulse generator, and a resistor to measure the capacitance of a length of cable. using the figure below, can get input and output of transient result, then measure the td(time delay). td=0.7RC, so C=td/0.7R
TEK00007.fw.png
C=(-12.9us)/(0.7)*(100k)=180*10^-12F
however, we can use the capacitance meter to measure the cable capacitance for comparing with the simulation result. 
Indeed, we can connect the cable to implement a test point on a PCB board after  adding a resistor and capacitor in parallel.

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