INF3410 — Fall 2016

Excerpt of Sedra/Smith Chapter 7: Integrated CMOSAmplifiers Basics

Content

Bias Current Steering (book 7.2)

CS, CG, and cascode configuration (book 7.3-7.5)

Improved Current Mirrors/Sources (book 7.6)

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Content

Bias Current Steering (book 7.2)

CS, CG, and cascode configuration (book 7.3-7.5)

Improved Current Mirrors/Sources (book 7.6)

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CMOS Current Steering

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Dynamic Input Currents, Current Amplifier

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Content

Bias Current Steering (book 7.2)

CS, CG, and cascode configuration (book 7.3-7.5)

Improved Current Mirrors/Sources (book 7.6)

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Intrinsic Gain from Small Signal

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Intrinsic Gain vs Bias Current

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CS Amplifier with Current-Source Load

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CS Amplifier Analysis

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Home Assignment last week: Inverter SmallSignal Analysis

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CG amplifier revisited

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Rin of a CG amplifier

vx = (ix + gmvgs)ro + ixRLExcerpt of Sedra/Smith Chapter 7: Integrated CMOSAmplifiers Basics 13

Rout of a CG amplifier

vx = (ix − gmvgs)ro + ixRLExcerpt of Sedra/Smith Chapter 7: Integrated CMOSAmplifiers Basics 14

CS with source degeneration no RL

RO ≈ (1+ gmRS)ro

gm→ g′m =gm

1+ gmRsNo net-increase in gain!

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CS with source degeneration with RL

Av = g′mRORL

RL +RO

≈ gmroRL

RL + (1+ gmRS)ro

... and more degradation to Av due toload RL!

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Cascode Amplifier

Can be looked upon as a CS and CG in series where theCS serves as high quality voltage controlled currentsource delivering id ≈ gm1vi and the CG buffers thatcurrent to a high output resistance ≈ gm2ro2ro1.

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Cascode Amplifier with Infinite LoadResistance

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Folded Cascode with Infinite Load Resistance

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Cascode Amplifier with Finite LoadResistance (1/2)

The load RL must be of equal magnitude as RO to getthe benefit of the increased gain AV! So here with asimple pFET we are back to square one.

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Cascode Amplifier with Finite LoadResistance (2/2)

Better: employ a cascoded current source.

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Content

Bias Current Steering (book 7.2)

CS, CG, and cascode configuration (book 7.3-7.5)

Improved Current Mirrors/Sources (book 7.6)

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Cascode Current Mirror

Increased output impedance, but quite a bit of outputvoltage headromm necessary ...

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Modified Wilson MOS Current Mirror

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A CD-CS Amplifier

Larger bandwidth than simple CSamplifier (explained later in chapter 9).

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