Lab 2 - EE 420L 

Mario Valles

January 23, 2015

• Show scope waveforms of a 10:1 probe undercompensated, overcompensated, and compensated correctly.
• This process was done by moving the compensator screw in the plug.
• The results were for the overcompensated the output has higher voltage at the start of the period, while the undercompensated had lower voltage. compesated was an expected square wave
• undercompensated
• 
• compensated
• 
• overcompensated
• 
  
• Comment on where the type of scope probe (i.e., 1:1, 10:1, 100:1, etc.) is set on your scope (some scopes detect the type of probe used automatically).
• This scope was set to 10x so it was on 10:1.
• 
  
• 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.
• 
  
• Here we are using a square wave functions
  
• Using circuit analysis, and reasonable/correct values for the capacitances, show using circuit analysis and alegbra (no approximations), that the voltage on the input of the scope is 0.1 the voltage on the probe tip.
• Calculation
• Z1 = (R1/(1/jwC2))/(R1+1/jwC2) = R1/(R1C2w + 1) 
• Z2 =(R2/(1/jwC2))/(R2+1/jwC2) = R1/(R1C2w + 1) 
• Vout/Vin = Z2/(Z1+Z2) = 0.1 V/V
  
• With the graph we obtained
• 
  
• 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. Make sure you show your hand calculations.
• From the meter we got
• 
• 
  
• about 10% of the input
  
• 
  
• The experiment I used gave the previous results
  
• calculations
• CT = 1/(jwRtan(x)) =(100k)(105p)(2pi)(tan(0.36)
• CT =414nF
  
• 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.
• The circuit builded was
• 
• The results we got with uncompensated probe was
• 
• With a compensated scope
• 
  
• Finally, 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.