Differential and Multistage Intensifiers - PowerPoint PPT Presentation

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Differential and Multistage Intensifiers

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  1. Differential and Multistage Amplifiers BJT & FET Differential Pair Small Signal Model Biasing March 08 2007

  2. Diff. BJT Amp. With Diff. Input • vB2=0, vB2=1 • Operate the first transistor in the active region conducting I, Q2 off VB1 VB2=0 March 08 2007

  3. Common Mode Input Voltage March 08 2007

  4. Differential pair with small input • For linear amplifier, apply small input, March 08 2007

  5. Large Signal Operation of BJT Diff. Amplifier • Nonlinear response to change in voltage differential March 08 2007

  6. Transfer Characteristic of BJT Diff. Pair • Linear only for small input! • Difference is limited to less than VT/2 March 08 2007

  7. Small Signal Model March 08 2007

  8. Simplified Model March 08 2007

  9. Diff Amp. w. Emitter Resistance March 08 2007

  10. Differential FET Amplifier Differential amplifier consists of two matched transistors which conduct the same current March 08 2007

  11. Common Mode Input Voltage March 08 2007

  12. Exercises 7.1, 7.2 March 08 2007

  13. Exercise 7.3 • V_DD and V_SS=1.5 V, k’_n(W/L)=4mA/V^2, V_t=0.5V, I=0.4mA, R_D=2.5k Ohm March 08 2007

  14. Diff. Amp. With Diff. Input • vG2=0, vG1=vid VG1 March 08 2007

  15. Large Signal Operation of MOSFET Diff. Amplifier • Nonlinear response to change in voltage differential March 08 2007

  16. Transfer Characteristic of FETDiff. Pair • Linear only for small input! • Difference is limited to V_ov March 08 2007

  17. Extending Linear Operation Range March 08 2007

  18. Small Signal Model MOS Diff March 08 2007

  19. Small Signal Analysis • Input and output Impedances March 08 2007

  20. March 08 2007

  21. Simplified Model Cut the differential pair into 2 March 08 2007

  22. Mismatch of g_m March 08 2007

  23. Offset Voltage to compensate March 08 2007

  24. Active load maintains bias current I Active load has high impedance Active Loads March 08 2007

  25. Active Load in Saturation Without any input Active Load March 08 2007

  26. The current generated by differential input will only flow to the load Active Load March 08 2007

  27. In practice, leakage from Drain to Source Active Load March 08 2007