OTA DESIGN and COMPENSATION

1
OTA DESIGN and COMPENSATION

• Two stage CMOS
• Feedback and Compensation

2
Basic Two Stage OTA/OPAMP

• Avol Av1 Av2
• GBP gm1/CL
• Lower input Noise than Folded Cascode
• Compensation- Miller and Pole-Zero cancellation
• Open Loop gain comparable to Folded Cascoded
• Wider Output Swing than Folded Cascode
• Lower GBP than Folded Cascode

3
General Observations regarding OpAmps
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Two Stage with Optional Buffer
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Two Stage with Optional Buffer
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Two Stage Frequency ac Response
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Pole-Zero and Miller compensation
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Slew Rate and Full Power Bandwidth
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p vs n Diff pair

• best SR/ mW
• Allows follower and gain stages poles further
  separation from the GBP
• Improved Noise performance due to 1/f behavior of
  PMOS vs NMOS
• In n-well processes n-follower can not be body
  tied

10
Feedback and OTA Compensation
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Feedback and OTA
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OTA Compensation pole splitting
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PHASE MARGIN
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REVIEW of 2ND ORDER SYSTEMS
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Pole-Zero Cancelation Model
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Pole-Zero Cancellation Model-2
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Pole-Zero Cancellation Model-2
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Pole-Zero Cancellation Design