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IN3170/4170, Spring 2020 Philipp Hfliger hafliger@ifi.uio.no - - PowerPoint PPT Presentation
IN3170/4170, Spring 2020 Philipp Hfliger hafliger@ifi.uio.no - - PowerPoint PPT Presentation
IN3170/4170, Spring 2020 Philipp Hfliger hafliger@ifi.uio.no Excerpt of Sedra/Smith Chapter 7: Integrated CMOS Amplifier Basics Content CG, and Cascode Configuration (book 7.4-7.5) Common Drain Stage/Source Follower (Book 6.3) CMOS Current
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CMOS Current Steering
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Computing Rref CMOS Current Steering
(live on whitebord) Wrong: using the small signal input resistance
1 gm for a desired ID
Correct: Use large signal model!!!
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Dynamic Input Currents, Current Amplifier
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Content
CG, and Cascode Configuration (book 7.4-7.5) Common Drain Stage/Source Follower (Book 6.3)
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CG amplifier
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Rin of a CG amplifier
vx = (ix + gmvgs)ro + ixRL ⇒ Rin ≈ 1 gm + RL gmro (7.54)
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Rout of a CG amplifier
vx = (ix − gmvgs)ro + ixRS ⇒ Rout ≈ ro + (gmro)Rs (7.58)
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Cascode Amplifier
Can be looked upon as a CS and CG in series resulting in a intrinsic combined gain A = gm1ro1gm2ro2 (i.e. with a large load resistance),
- r a circuit where the CS serves as high quality voltage controlled
current source delivering id ≈ gm1vi and the CG buffers that current to a high output resistance ≈ gm2ro2ro1.
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Cascode Amplifier with Infinite Load Resistance
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Cascode Amplifier with Finite Load Resistance (1/2)
The load RL must be of equal magnitude as RO to get the benefit
- f the increased gain AV ! So here with a simple pFET we are back
to square one.
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Cascode Amplifier with Finite Load Resistance (2/2)
Better: employ a cascoded current source.
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Dependency of Gain on RL
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Content
CG, and Cascode Configuration (book 7.4-7.5) Common Drain Stage/Source Follower (Book 6.3)
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Common Drain Amplifier/Source Follower
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