(9)Folded Cascode (cont

Chapter 9 p

Operational Amplifiers

Important Parametersp

Gain

Small-Signal Bandwidth Small Signal Bandwidth Large-Signal Bandwidth

O t t S i Output Swing

Linearity

Noise and Offset Supply Rejection Supply Rejection

One-Stage Op Ampsg p p

One-Stage Op Amp in Unity Gain C fi ti

Configuration

Cascode Op Ampsp p

Unity Gain One Stage Cascodey g

Folded Cascode Op Ampsp p

Folded Cascode Stages (cont.)g ( )

Folded Cascode (cont.)( )

Folded Cascode (cont.)( )

| A_v |≈ g_m1{[(g_{m 3} + g_mb3)r_o3 (r_o1 || r_o5 )]|| [(g_{m 7} + g_{mb 7})r_o7r_o9 ]}

| _v | g_m1{ (g_{m 3} g_mb3) _o3 ( _o1 || _o5 ) || (g_{m 7} g_{mb 7}) _{o7 o9} }

Telescopic vs. Folded Cascode Polep

Example Folded-Cascode Op Ampp p p

See Example 9.6

Single-Ended Output

C d O A

Cascode Op Amps

Triple Cascodep

A_v app. (g_mr_o)³/2 Li it d O t t S i Limited Output Swing

Complex biasing

Two-Stage Op Ampsg p p

Design Approach for Two-Stage Op Amps Design Approach for Two Stage Op Amps

Single-Ended Output

T St O A

Two-Stage Op Amp

Simple Implementation of a Two-p p Stage Op-Amp

Two-Stage Op-Amp employing g p p p y g Cascading

Output Impedance Enhancement With F db k

With Feedback

Rout = A₁g_{m 2}r_o2r_o1

Gain Boosting in Cascode Stageg g

Differential Gain Boostingg

Differential Gain Boosting (cont.)g ( )

Differential Gain Boosting (cont.)g ( )

Gain Boosting applied to both g pp signal path and load devices

Comparisonp

Common-Mode Feedback

Common-Mode Feedback (cont.)( )

High Gain Amp Modelg p

Common-Mode Feedback (cont.)( )

Resistive Sensingg

Source-Follower Bufferingg

Deep Triode FET CM Sensingp g

CMFB Examplep

Alternative CMFB for Folded

C d

Cascode

Simplified CMFB with Triode D i

Devices

CMFB Triode Example with Referencep

CMFB Triode Example with

R f ( t )

Reference (cont.)

CMFB Triode Example with

R f ( t )

Reference (cont.)

Differential Pair with CMFB

Input Range Limitationsp g

Unity-Gain Buffer

Extension of Input CM Rangep g

Variation of equivalent transconductance with the input CM level

with the input CM level

Two Folded Cascode op amp Two Folded Cascode op amp

with constant equivalent transconductance

Slew Rate

Linear RC Step Response

Slewing in Op Ampg p p

Small-Signal Operation of Op Ampg p p p

Op Amp Slewingp p g

Slew rate = V/S = I/C

Op Amp Slewing (cont.)p p g ( )

Slewing in Telescopic Op Ampg p p p

Folded-Cascode Slewingg

Folded-Cascode (cont.)( )

Slewing Recoveryg y

Slewing Recovery (cont.)g y ( )

Power Supply Rejectionpp y j