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EE 420L |
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AUTHOR: Henry
Mesa |
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Experiment 1: Show scope waveforms of a 10:1 probe undercompensated, overcompensated, and compensated correctly.
Attenuation Adjustment of Tektronix TDS Oscilloscope:
Compensated Scope Probe Overcompensated Scope Probe Undercompensated Scope Probe   
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Experiment 2: Draft
the schematic of a 10:1 scope probe showing: the 9 MEG resistor, 1 MEG
scope input resistance, capacitance of the cable, scope input
capacitance, and capacitance in the probe tip.
10:1 Scope Probe Attenuation Factor:
Hand Calculations to Detail Circuit's Operation:
Input
Capacitance + Cable Capacitance = 20pF + 99pF = 119pF
Probe Capacitance = 119pF
÷
9 = 13.22pF
Therefor, we can appreciate that the attenuation factor has been proven.
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Experiment 3: Devise
an experiment, using a scope, pulse generator, and a resistor, to
measure the capacitance of a length of cable. Compare your measurement
results to the value you obtain with a capacitance meter.
Schematic(Theory):  Hand Calculations to Detail Circuit's Operation:
Comparing
Hand Calculations, Simulation, and Experimental Results:
Cable length: A good estimate for the capacitance of a cable is 100pF/m. Coinciding with the length of the cable I used for the experiments about 1 meter long. |
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| Experiment 4: Build
a voltage divider using two 100k resistors. Apply a 0 to 1 V pulse at 1
MHz to the divider's input. Measure, and show in your report, the
output of the divider when probing with a cable (having a length
greater than or equal to 3 ft) and then a compensated scope probe.
Discuss and explain the differences. Schematic:  Schematic(Uncompensated Scope) :  Schematic(Compensated Scope) :  Experimental Results: Circuit  Uncompensated Scope Probe Compensated Scope Probe   The uncompensated scope probe has gater capacitance as well as geater time delay. This large capacitance coupled with the impedance of the oscilloscope, leads to a large RC time constant. A frequency of 1 MHz is so large that, the signal is never able to ever charge fully. Thereby, giving us what appears to be a flat voltage trace in comparison with the compensated scope probe. | ||||||||||||
Experiment 5: briefly
discuss how you would implement a test point on a printed circuit board
so that a known length of cable could be connected directly to the
board and not load the circuitry on the board. The capacitor contained within each resistor-capacitor block will be a variable capacitor. This will give us the avility to be adjusted based on the length of the cable connected to the PCB terminal. Therefor, fixing the capacitance of the cable or probe and giving us the certainty of not overloading the circuit being tested. |
