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Miller-OTA Opamp design

Miller-OTA Opamp design. In AMIS CMOS 07 by Roman Prokop. Simple Miller-OTA Opamp with follower. All MOSes should work in saturation region – then their parameters are following:. N A – substrate doping ~ X .10 16 cm -3. Simple Miller-OTA Opamp AC hand calculation.

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Miller-OTA Opamp design

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  1. Miller-OTA Opamp design In AMIS CMOS 07 by Roman Prokop

  2. Simple Miller-OTA Opampwith follower All MOSes should work in saturation region – then their parameters are following: NA – substrate doping ~ X .1016 cm-3

  3. Simple Miller-OTA OpampAC hand calculation AC small signal linearized model

  4. Simple Miller-OTA OpampAC hand calculation Redrawing - simplification

  5. Simple Miller-OTA OpampAC hand calculation – A0=? small ~1

  6. Simple Miller-OTA OpampAC hand calculation – fp1=?We know, where it is Follower neglected

  7. Simple Miller-OTA OpampAC hand calculation – fp1=?

  8. Simple Miller-OTA OpampAC hand calculation – fp1=?

  9. Simple Miller-OTA OpampAC hand calculation – fp1=? 3 possibilities a) No R, no C;G=0 Confirmation of the transfer function without R&C

  10. A0 Simple Miller-OTA OpampAC hand calculation – fp1=? b) No R, only C;G=jωC

  11. R - negligible Zero is moved if R=1/gm7 fZ=∞ Pole without changes A0 Simple Miller-OTA OpampAC hand calculation – fp1=? c) R & C (R added);G=(R+1/jωC)-1

  12. Simple Miller-OTA OpampAC hand calculation GBW – Gain band width =?

  13. Simple Miller-OTA OpampAC hand calculation First non-dominant pole -> stability =? 1st non-dominant pole decides about stability. if fND1> GBW stable We have 3 ND poles. We are interested in the lowest one. ad 1)C1 is small (high f) C1 shorts the V1 to the ground

  14. ad 2)the most usual case • At this frequency we expect CC is a short • we get diode with gm7 >> other G Stability condition - approx. 3 < If there is no close other pole !!! estimate !!! Simple Miller-OTA OpampAC hand calculation First ND pole

  15. Simple Miller-OTA OpampAC hand calculation First ND pole ad 3)caused by load capacitance It can appear if Cload is bigger capacitance Then expecting Cload >> ΣCds,Cdg

  16. ICC:=min (IB,I4) Usually I4 > IB depends on IB Simple Miller-OTA OpampAC hand calculation SR – Slew rate Input goes rail to rail all IB current flows either through M1, M5, M6 or through M2

  17. Simple Miller-OTA OpampDC hand calculationDC input range

  18. Simple Miller-OTA OpampDC hand calculationDC input range Be careful for temperature and process worst case

  19. To suppress the offset Simple Miller-OTA OpampDC hand calculation – structure offset This systematic offset usually appears when Vds5≠ Vds6 Vds6 depends on Vgs7

  20. Simple Miller-OTA OpampDC hand calculation Matching offset The first stage gives the most significant contribution to the offset. Contribution of the second stage is negligible because of the first stage gain.  Usually sufficient for hand calculation Result is valid for 1σ statistical result - use value (4σ÷6σ) for offset calculation

  21. MatchingAMIS CMOS07 parameters - NMOS Carefully: units mV, μm, %

  22. MatchingAMIS CMOS07 parameters - PMOS Carefully: units mV, μm, %

  23. Stability condition - approx. 3 < Simple Miller-OTA OpampHand calculation - Conclusion - AC

  24. Simple Miller-OTA OpampHand calculation - Conclusion - DC DC input range Matching offset

  25. Simple Miller-OTA OpampSimulation - AC Possible tested parameters: A0 - DC gain GBW – Gain bandwidth fp1 - The first pole frequency ~ fND1 - The first non-dominant pole frequency AM, PM – Gain margin, Phase margin

  26. Simple Miller-OTA OpampSimulation - DC Possible tested parameters: OFFSET - Input asymmetry - systematic offset - matching offset CM – DC input range

  27. Simple Miller-OTA OpampSimulation – DC input range Possible tested parameters: OFFSET - Input asymmetry - systematic offset - matching offset CM – DC input range

  28. Good luck !!!

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