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EE100Su08 Lecture #10 (July 18 th 2008)

EE100Su08 Lecture #10 (July 18 th 2008). Outline Midterm #1: pick it up from me in OH today HW #1: Pick up from labs HW #2: should be returned next week HW #1 and Midterm #1 regrade deadline: Wednesday, July 23 rd 2008, 5:00 pm PST. Procedure: HW #1: Bart’s office hours

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EE100Su08 Lecture #10 (July 18 th 2008)

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  1. EE100Su08 Lecture #10 (July 18th 2008) • Outline • Midterm #1: pick it up from me in OH today • HW #1: Pick up from labs • HW #2: should be returned next week • HW #1 and Midterm #1 regrade deadline: Wednesday, July 23rd 2008, 5:00 pm PST. Procedure: • HW #1: Bart’s office hours • Midterm #1: Attach a note to the FRONT of your test with your complaint and drop it in HW box • Questions? • This week: Operational Amplifiers (Op-Amps) • Nonlinear circuits • More examples • MultiSim Examples • Op-Amp from 2-Port Blocks

  2. + - + - Summing Amplifier v1 R1 R0 v2 R2 v0 _ + + - v3 R3

  3. + - Difference Amplifier R2 v1 R1 v0 _ + + - R3 v2 R4

  4. R + + V0 C - - Integrator • Want • What is the difference between: vin

  5. R C v0 _ + vin + - Differentiator • Want

  6. Nonlinear Opamp Circuits • Start reading through online notes: “Introduction to nonlinear circuit analysis”. • Outline: • Differences between positive and negative feedback. • Oscillator circuit.

  7. AMPLIFIER SYMBOL AMPLIFIER MODEL Differential Amplifier Circuit Model in linear region V0 V+ + A AV1 Ri  V +  V0 depends only on input (V+  V-) + + V0 V1   High Quality Dependent Source In an Amplifier See the utility of this: this Model when used correctly mimics the behavior of an amplifier but omits the complication of the many many transistors and other components.

  8. Model for Internal Operation • A is differential gain or open loop gain • Ideal op amp • Common mode gain = 0 • Circuit Model + i1 v1 Ro io Ri vo i2 v2 + – _ A(v1–v2)

  9. Negative feedback connecting the output port to the negative input (port 2) Positive feedback connecting the output port to the positive input (port 1) Input impedance: R looking into the input terminals Output impedance: Impedance in series with the output terminals + i1 v1 Ro io Ri vo i2 v2 + – _ A(v1–v2) Model and Feedback • Circuit Model

  10. R1 R2 R1 R2 V0 VIN AV1 Ri + VIN  Summing Point Circuit Model + - V1 V0 +  - + Op-Amp and Use of Feedback A very high-gain differential amplifier can function in an extremely linear fashion as an operational amplifier by using negative feedback. Negative feedback  Stabilizes the output Hambley Example pp. 644 for Power Steering We can show that that for A   and Ri  , Stable, finite, and independent of the properties of the OP AMP !

  11. 0 0 1 0 1 10K 0 0 1 1 1.5 S4 0 1 0 0 2 20K 0 1 0 1 2.5 S3 0 1 1 0 3 40K S2 8V 0 1 1 1 3.5 + - 5K 80K 1 0 0 0 4 - 1 0 0 1 4.5 + - V0 S1 1 0 1 0 5 + 1 0 1 1 5.5 4-Bit D/A 1 1 0 0 6 1 1 0 1 6.5 1 1 1 0 7 1 1 1 1 7.5 Application: Digital-to-Analog Conversion A DAC can be used to convert the digital representation of an audio signal into an analog voltage that is then used to drive speakers -- so that you can hear it! Analog Binary output number (volts) 0 0 0 0 0 0 0 0 1 .5 “Weighted-adderD/A converter” S1 closed if LSB =1 S2 " if next bit = 1 S3 " if " " = 1 S4 " if MSB = 1 (Transistors are used as electronic switches) LSB MSB

  12. Characteristic of 4-Bit DAC 8 7 6 5 Analog Output (V) 4 3 2 1 0 0 2 4 6 8 10 12 14 16 0000 0001 1111 1000 0100 Digital Input

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