Lab 8/Experiment 17

A Differentiator Circuit

First Issue

• If anyone has a US Gear sound card that is not in a plastic case, we will replace your card.– Please contact Mr. Lineberry at

https://helpdesk.ece.vt.edu/helpdesk/index.php

Second Issue

• If anyone of you are planning to purchase an oscilloscope in the near future, please look at the spec sheet that I will post shortly on our Blackboard site.

Third Issue

• Extra Credit Lab– Students may do one extra lab, selected from one of the labs in

the manual that was not assigned during the semester, and it will count for a maximum of an additional 5% to their lab grade.

– Students will also be able to do an extra credit design project for a maximum of an additional 10%. The design project will require a proposal submitted at least 2 weeks before the deadline and the proposal must be approved for the work to be used towards the student’s grade. Students may choose their design project but it must be significant, implement something interesting, and build upon the concepts learned in the course.

– All extra credit lab reports and validations must be completed by 12/3/2009.

Fourth Issue

• The incorrect experiment number is listed in the syllabus for this week’s lab. – It is Experiment 17, not Experiment 12.

Modification to Experiment 17Modeling: Step 6• Perform an AC Sweep in Pspice using the

component values computed in step 2– You do not need to make a plot of the voltage as a

function of frequency; the plot generated by Pspice is sufficient.• Use a uA741 Op Amp as there is not a LF 356 part in the

student version of PSpice.• Frequency to be sweep is 500Hz to 5000Hz• VAC must be used as the input voltage supply to obtain a

plot of the signal as a function of frequency. – VSIN is only used when performing a transient analysis.

Source shown in Figure 1 is VSIN

AC Sweep with VSINResult in either Capture or Schematics is an error message.

AC Sweep with VAC: Capture

Maximum value of sinusoidal voltage

Value of a DC voltage added to sinusoidal voltage

Frequency to begin and end the AC Sweep and the number of points

calculated and plotted.

AC Sweep with VAC: SchematicsDouble click on the 0V to set the magnitude of the sinusoidal input voltage

Frequency to begin and end the AC Sweep and the number of points

calculated and plotted.

Red is the input voltage

Green is the output voltage

Useful Information

• Unity gain (A = Vo/Vin = 1) is when the output voltage equals the input voltage.

• Decibels dB = 20 log (Vo/Vin)

where Vo is the output voltage and Vin is the input voltage

dB = 10 log (Po/Pin)where Po is the power dissipated by the load resistor and Pin is the power supplied to the circuit by Vin

• Angular frequency (w) vs. Frequency (f)w = 2pfw = (RC)-1 for the circuit in Figure 1