EL3203: Analog Circuits Lab, Jan.-May 2014

• Aniruddhan S
• Nagendra Krishnapura

• P slot(Mondays, 2-445pm) in the IE lab.

The lab will be kept open on Saturdays from 9am to 12pm and 2pm to 5pm for you to assemble/debug your circuits.

• Your grade will be based on evaluations of weekly experiments, a final lab project, and a written test which will be conducted at the end of the semester.
  • Lab sessions(40%)
  • Final project(30%)
  • Written test(30%)

• The lab sessions are meant for verification and measurement of circuits that you design, and not for assembly. Assemble your circuits before coming to the lab session. The experiments will be posted in advance on this page.
• Tidy up at the end of the session: Clean up your table, push the stools you used under the table, return any borrowed components to the staff in charge
• Notify staff of defective equipment
• If you are unable to finish an experiment in a session, move on to the next in the following session. If you finish that early, go back to the earlier experiment and complete it. You can also use the Saturday sessions to finish incomplete experiments. But you can show them to the TAs for grading only in the regular lab sessions.

• Attendance will be strictly enforced and those falling short will receive a W
• Sign in your attendance with the TA as you enter the lab. If you arrive more than 10 minutes late to the lab, you will not be admitted

• EC3102 Analog circuits
• Read XYZ's of oscilloscopes paying particular attention to pages 3-10,11,18-23,27-31. You should understand oscilloscopes to make meaningful measurements
• Read component data sheets in the last section of this page

• Go through the data sheets of relevant components for each experiment
• Wire up the circuit (neatly!) before coming to the lab session. No debugging assistance will be given for overly messy wiring. Use colour coded wiring-i.e. red for positive supply, black for ground, green for negative supply, and others for signals. Cut wires to appropriate lengths so that they can be routed flush on the breadboard instead of forming messy loops over it. The same goes for resistors.
• Test your circuit during the lab session
• Maintain a lab notebook in which you briefly record the results and troubleshooting information
• Be familiar with component pinouts. You don't want to be connecting opamps in positive feedback or driving the outputs of gates with signals.
• Draw schematics of the experiments with expected bias voltages, bias currents, and signal levels marked on them. This is a very good debugging aid.

List of Components: Each group must have the following Get the component kit from IE lab after 3pm.

• Breadboard (2)
• Wire stripper (1)
• Nose pliers (1)
• Hook up wire (single strand): 4m each of red, blue, yellow, green, black
• Digital Multimeter (1)
• BNC to alligator cables (4)
• ICs: CD4069(4), MC1496(2), LF347(5), LM311(2), 74LS00(2), 7402(2)
• Transistors: BC107(8), BC177(8)

Information for experiments will be put up on this page in advance so that you can come prepared to the lab. Familiarise yourselves with the characteristics of the components by reading the data sheets of the components given below. Many experiments are based on using CMOS inverters as transconductors. Understand the principles by going through this lecture.

1. 27 Jan. 2014: Inverter characteristics (View the lecture)
2. 3 Feb. 2014: Amplifier compensation
3. 10 Feb. 2014: Voltage regulator
4. 17 Feb. 2014: Voltage regulator
5. 24 Feb. 2014: Charge pump -ve voltage gen.
6. 3 Mar. 2014: Gm-C filter
7. 10 Mar. 2014: Active RC filter (Lecture)
8. 18 Mar. 2014: Oscillator(Lecture)
9. 24 Mar. 2014: Mixer (Lecture)
10. 7 Apr. 2014: Double balanced mixer (Lecture)
11. 16 Apr. 2014: Final project
12. 21 Apr. 2014: Final project
13. 28 Apr. 2014: Final exam

Go through these data sheets before wiring up the circuit. Pay particular attention to pinouts, power supply polarity, and maximum voltage ratings.

• CD4069 CMOS Hex inverter
• LM324 Quad opamp(0.5MHz gain bandwidth product)
• LF347 Quad opamp(FET input, 4MHz gain bandwidth product)
• LM311 comparator
• MC1496 double balanced modulator
• BC107 NPN transistor
• BC177 PNP transistor

See this link for a short description of different capacitor types. Use polyester film capacitors(yellow box) for filters.

Whenever a circuit isn't behaving as expected, it pays to go through these steps systematically. This also applies when you simulate circuits and the results aren't as expected.

• Verify that the power supplies and signal sources are on, and are correctly connected to the board.
• Measure the power supplies and bias points, at the component pins. You may have “wired up” the circuit with loose wires or altogether incorrectly. This is where the schematic with expected bias and signal levels will be a great help
• Bias points: Check these with a multimeter. Note that the multimeter's input resistance of 10MΩ, while much larger than the impedance of most circuits you will be dealing with, can disturb the bias of high impedance circuits.
  • supply levels
  • opamp inputs should be virtual shorts
  • opamp outputs should be well within swing limits for the given supplies
  • transistors' base-emitter drop should be about 0.65 V
  • transistors must be in their active regions(CB reverse biased)
• Signal levels: You need to check these with an oscilloscope. An oscilloscope's input impedance (approx 1MΩ in parallel with 100pF) can disturb high frequency circuits. So use 10x mode where necessary. Generally many circuits we use are excited with periodic inputs and it is convenient to check the signals progressively through the circuit, starting from the input.

• Measuring “AC” voltages with the multimeter: The digital voltmeter typically measures the average value of the rectified input and gives you readings in rms Volts assuming that the input is a sine wave. The readings will be horribly off if the input is not a sine wave. Also, the frequency response of the multimeter is only upto about 500Hz. So do not use the multimeter to measure ac signals unless you are absolutely sure of what you are doing.
• Do not measure differential signals with the oscilloscope by connecting the two leads to the two voltages. The ground terminal of the oscilloscope *must be* connected to the circuit ground. Otherwise some part of the circuit will get shorted out through the grounds of oscilloscope and power supply and the mains ground.
• Short the two power supply rails on the breadboard near the end at which the power supply is connected, not the far end. This will minimize the voltage drop across the power supply and ground leads. Excessive supply/ground drops can induce weird behaviour in the circuit. See this picture.