End of Semester Info

• Exam questions available on class web page: 2 of the 4 questions posted at the “question bank” link will be chosen for the exam

• Practice for the exam week after next during class (Nov 24,25). You are not required to come, but are strongly encouraged to do so. Your TA will run these classes.

• redo’s of the first lab report are also due Nov 24, 25

• The exam is Dec 1/2.

• Please check ELMS and make sure all your grades are correct. I have not graded the lab 1 re-submits yet. Let me know ASAP if any of the grades is wrong. Reports of incorrect grades for the items that I have graded as of today will not be accepted after Dec 2.

Lab #7: Diode and Rectifier Circuits

• learn what diode is

• learn some simple circuits that use diodes

No lab report, just excel spreadsheet

Diode•Energy levels of electrons in atoms are quantized (1s, 2s, 2p, etc)

•When these atoms are brought together in crystals, these energy levels become energy bands with gaps between them.

• Because of the “Pauli exclusion principal” no 2 electrons can have the same quantum numbers.

• The distributions of electron energies depends on the temperature. The highest possible energy when T=0 is called the Fermi Energy (EF).

• some materials can be made into semi conductors by adding small amounts of impurities. p-type (one fewer valence e than Si) and n-type (one more valence than Si).

• semi conductors do not conduct at T=0.

1 eV

Diode

Electrons migrate from n to the holes in p, giving a net charge to each side (neg on p side, pos on n side)

104 – 106 V/cm, 0.3-0.6 V

In steady state, there are conduction electrons who have enough thermal energy to go over the potential barrier and make a (positive) current from p to n. There is an equal and opposite current of electrons that get enough thermal energy to break their bonds in the p region, go up into the conduction band, and then slide down the barrier back to the n region.

Diode

+ - - +Here, the external bias aids the electrons trying to go from n-p and you get a net current in the p to n direction. (when the voltage is larger than the gap voltage, typically 0.6 V)

/0( 1)qV kTI I e= −

Here, the external voltage stops the electrons going from n to p. The ones going from p-n can still go and you get a (small) net current from n to p (the prob to get enough thermal energy to break the bond is unchanged)

Diode

/0( 1)qV kTI I e= −

symbol Idealized I vs V

Realistic I vs V

Half-wave rectifier

Full wave rectifier

RC differentiator

See pg 36

For t>>RC. Voltage across resistor is derivative of VIN

frequency to voltage converter

Hints

• lab begins pg 70 no error analysis this lab

• IV.A. Do 10 measurements.. RMS, not peak-to-peak, Try pulling/pushing the amplitude knob on the scope. You should be able to go up to about 7.5V and down to 0.2 or 0.1 V.

• IV.A fit the upper points (the part that looks linear) to a straight line, extrapolate the line down to the lower points. Include a graph with all the points and the line.

• IV.B. in this part, and in subsequent parts, it is very important that the peaks be of equal size, and not alternating small, big, small, big. The peaks should occur at both the max and min of the driving frequency. If this does not happen, adjust the offset on the driving signal until it does.

•IV.B Replace the last sentence with: For 3 different generator voltages, measure the peak-to-peak and RMS voltages for both the generator and load voltage. For each, make a plot of generator versus load, fit to a straight line, and comment on the slope and x-intercept

Hints

•IV.C. Be careful! Not the normal cap• IV.C. Replace instructions with: Set the frequency generator amplitude to about 3 Volts. for 8 different values of the frequency, plot the mean and peak-to-peak voltage across the cap versus frequency. Make sure at least 4 of the frequencies are between 20 and 100 Hz, and the highest is around 60 kHz. When measuring the mean, make sure the scope input is DC coupled. When measuring the peak-to-peak, make sure it is AC coupled and that the scale is set to a small enough setting that you can see structure. Use the cursors, not measure for the peak-to-peak. At very high frequencies, the structure will go away. Report 0 for the peak-to-peak.

Hints

• skip V-A, V-B, and V-C