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

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

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

4. Simple Miller-OTA Opamp AC hand calculation
Redrawing - simplification

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

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

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

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

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

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

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

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

13. Simple Miller-OTA Opamp AC 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. Simple Miller-OTA Opamp AC hand calculation First ND pole
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 !!!

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

17. Simple Miller-OTA Opamp DC hand calculation DC input range

18. Simple Miller-OTA Opamp DC hand calculation DC input range
Be careful for temperature and process worst case

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

20. Simple Miller-OTA Opamp DC 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. Matching AMIS CMOS07 parameters - NMOS
Carefully: units mV, μm, %

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

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

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

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

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

28. Good luck !!!