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741 Op-Amp Circuit

741 Op-Amp Circuit . Section 8.1 ( Razavi ) Chapter 12 ( Sedra Smith). History. The first uA741 Op-Amp was designed by Bob Widlar in 1963 at Fairchild Semidconductor . uA702 sold for 300 a piece. uA709 was sold for 70 a piece.

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741 Op-Amp Circuit

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  1. 741 Op-Amp Circuit Section 8.1 (Razavi) Chapter 12 (Sedra Smith)

  2. History • The first uA741 Op-Amp was designed by Bob Widlar in 1963 at Fairchild Semidconductor. • uA702 sold for 300 a piece. • uA709 was sold for 70 a piece. • Bob asked for a raise, didn’t get it, so he quit. Bob sent to National Semiconductor. • LM101 http://en.wikipedia.org/wiki/Bob_Widlar

  3. History • David Fullagar (Fairchild) • Scrutinize LM 101 • Incorporated a 30 pF Cap. • uA741 was introduced. • Gordon Moore

  4. BJT Op-Amp

  5. BJT Op-Amp Input-Stage Bias Reference Bias Current Second-Stage Input-Stage Output-Stage

  6. Reference Bias Current VCC=15 V VEE=-15 V VBE11=0.7 V VEB12=0.7 V IREF=0.73 mA

  7. Input-Stage Bias IREF=0.73 mA R4=5 KΩ (IS10=IS11, assumption) Solve through trial and error IC10=19 uA

  8. Input Stage (1) From previous Calculation: IC10=19 uA (from symmetry) (β is high ) (~0)

  9. Negative Feedback (2) (3) (1) (4) (constant)

  10. Input Stage (2)

  11. Input Stage (3) (IB1) (IB2) (Input Bias Current) (Input Offset Current)

  12. Input Resistance (1) (AC Ground)

  13. Input Resistance (AC Ground) R into the emitter of Q3: 1/gm3 R into the base of Q1: rπ1+β1/gm3 Differential resistance 2(rπ1+β1/gm3) gm=IC/VT Large input resistance since IC is kept small! Typical input impedance is in excess of 2 MOhms

  14. Second-Stage Bias 0.75IS12=IS13B IC12=0.73 mA IC13B=0.55 mA IC17=IC13B (0)

  15. Class AB Output Stage (Review)

  16. Output Stage Bias (0) IS13,A=0.25IS12 IC23=0.25IREF Assume VBE18=VBE19=0.6 V Βp=50 Βn=200 ICE23=180 uA IR10=15 uA IE18=IE23-IR10 IB18=IC18/200=0.8 uA IE19=IB18+IR10 VBB=VBE18+VBE19 (Output resistance is small) (0)

  17. Op-Amp

  18. Equivalent Circuit of an Op-Amp Characteristics: Negligible input current Large input AC resistance Small AC output resistanceLarge Voltage Gain

  19. Op-Amp as an Amplifier (non-inverting input) (inverting input) Op-Amp is a circuit that amplifies the difference between the inputs.

  20. Inverting/Non-Inverting Configuration

  21. Consequence of Large Gain As Ao approaches infinity, Vin1-Vin2 approaches 0.

  22. Unity Gain Buffer (If A0 is 1000, Vout/Vin=0.999)

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