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Active Analogue Circuits Year 2

Active Analogue Circuits Year 2. B. Todd Huffman. CP2 Circuit Theory Revision Lecture. Basics, Kirchoff’s laws, Thevenin and Norton’s theorem, Capacitors, Inductors AC theory, complex notation, LCR circuits Passive Sign Convention ( NEW!!! ) Example of PSC use ( also NEW )

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Active Analogue Circuits Year 2

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  1. Active Analogue CircuitsYear 2 B. Todd Huffman

  2. CP2 Circuit Theory Revision Lecture Basics, Kirchoff’s laws, Theveninand Norton’s theorem, Capacitors, Inductors AC theory, complex notation, LCR circuits • Passive Sign Convention (NEW!!!) • Example of PSC use (also NEW) • Good Texts: • Electronics Course Manual for 2nd year lab. • “Art of Electronics” by Horowitz and Hill October 2013 Todd Huffman

  3. +IR1 + – –V0 +IR2 + + – – +IR1 + – Kirchoff’s laws I1 I2 I1+I2–I3–I4=0 I3 I4 -V0+IR1+IR2+IR3=0 R1 I R2 V0 R3

  4. Thevenin and Norton theorem Req Veq  Req In Practice, to find Veq, Req… RL (open circuit) IL0 Veq=VL RL0 (short circuit) VL0 Req= resistance between terminals when all voltages sources shorted and current sources opened.

  5. Capacitors Q = CV +Q C -Q Capacitors resist change in voltage • Capacitors in series • Capacitors in parallel • Stored energy stored in form of electric field C1 C2 CN

  6. Inductors • Inductors in series • Inductors in parallel • Stored energy stored in form of magnetic field Inductors resist a change of current L “back emf” Self-inductance L1 L2

  7. AC circuit theory • Voltage represented by complex exponential • Impedance relates current and voltage V=ZIin complex notation: Resistance  R Inductance  jL Capacitance 1/jCand combinations thereof • Impedance has magnitude and phase represented by real component of easily shown from Q=VC

  8. Current is given by • So |Z| gives the ratio of magnitudes of V and I, and  give the phase difference by which current lags voltage

  9. Passive Sign Convention Passive devices ONLY - Learn it; Live it; Love it! R=Resistance Ω[ohms] Two seemingly Simple questions: Which way does the current flow, left or right? Voltage has a ‘+’ side and a ‘-’ side (you can see it on a battery)on which side should we put the ‘+’? On the left or the right? Given V=IR, does it matter which sides for V or whichdirection for I?

  10. + – + + – – + – AC circuit Example Answer! -V0+IR1+(I+I0ejf)/(jwC)+IR1=0 R1 I0ejf V0 I 1/jwC R1

  11. The Transistor! Go to diode part of lecture

  12. Simple Transistor Model • It can be a “switch” • Flow is “on” one way • Flow is “off” the other way • It can be an amplifier • The flow is proportional to the amount you turn the valve. • If you turn the valve fast enough you can communicate in Morse-Code-litres

  13. Bipolar Junction Transistor curves On black board!

  14. First Transistor Small Signal Model Model works for npn and pnp(follow passive sign conv. on resistor) collector base + – vBE gmvBE b/gm Typical npn form shown emitter

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