Lab 2 - EE 420L
Author: Victor Payumo
Date: February 5, 2020
Email: payumo@unlv.nevada.edu
Operation of a compensated scope probe
Experiment 1: Scope waveforms of a 10:1 probe
Undercompensated
Overcompensated
Compensated
Verifying with LTspice:
Here the capcitance is too low @ 5pF (undercompensated)
Here the capcitance is too high @ 15pF (overcompensated)
Here the capacitance is sufficient @ 11.7 pF (compensated)
The menu to manually adjust the attenuation on a probe after pressing the corresponding channel button and then selecting probe
Circuit Analysis of 10:1 probe:
Experiment 2: Measuring capacitance of a cable using RC circuit model
We
can implement an RC circuit in order to calculate the capacitance of a
~3 ft. coaxial cable by connecting it in series with a resistor.
Using the equation T = R*C (R = 100 K @ 10 KHz):
C = 10 us / 100 K = 100 pF
Measurement using the multimeter gives 103 pF
Experiment 3: Voltage divider
The
following waveforms are the output signals of a 100 K resistor in
series with another 100 K resistor using respective probing. A pulse of
1 V was supplied @ 1 MHz.
Coaxial cable
Compensated probe
There
is a higher rise/fall in the output voltage of the divder that is
probed with a 10:1. This is because the 10:1 circuit goes through an
extra divider (the 100k in series with 100k) thus accelrating the
charge/discharge time of the capacitors.
Test point on a PCB
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