advanced analog integrated circuits - people

B. E. Boser 1

Advanced Analog Integrated Circuits

Part IIBernhard E. Boser

University of California, [email protected]

Copyright © 2016 by Bernhard Boser

EE240B – Part II

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Implementation Issues

EE240B – Part II

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Biasing

Bernhard E. BoserUniversity of California, Berkeley

[email protected]


EE240B – Biasing

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Transistor Biasing

• Design Parameter– 𝑔#, 𝑉∗, 𝑓(

• Layout Parameter– 𝑊, 𝐿– Fingers 𝐹– Multiplicity 𝑀

EE240B – Biasing

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Example

EE240B – Biasing

Spectre Syntax:op1 dc oppoint=screen

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Operating Point AnalysisInstance: M1 of nmos3

Model: nfet.4Primitive: bsim3v3

d : V(v_ds) = 523.447 mVg : V(v_gs) = 523.447 mVs : val(0) = 0b : val(0) = 0

type = nregion = sat

reversed = noids = 60.037 uA

isub = 41.0222 aAvgs = 523.447 mVvds = 523.447 mVvbs = 0 Vvgb = 523.447 mVvdb = 523.447 mVvgd = 1.32916 pVvth = 502.512 mV

vdsat = 78.9438 mVvfbeff = -1.00379 V

gm = 1.00019 mSgds = 18.5458 uS

gmbs = 283.567 uS...

EE240B – Biasing

Check operating point and beware of shifts during large transients!

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Current Sources


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EE240B – Biasing

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Current Source Realization: Mirror

EE240B – Biasing

Choices for Iref: resistor, bandgap, constant gm reference, …

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Cascode Bias

EE240B – Biasing

• Choose 𝑊- ≅ /012 such that 𝑉345 ≅ 𝑉5∗ + 50mV (use lookup)

• Note: ok for cascodes to have different W/L• Insensitive to body-effect

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Bias Network Power Dissipation

Minimize:

• Share bias network between several amplifiers

• Ratio mirror

EE240B – Biasing

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Noise


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EE240B – Biasing

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Noise

EE240B – Biasing

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Low Noise Current Source

Active (BJT or MOS) Resistor

EE240B – Biasing

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Class of Operation

• Class A ß focus in this course– Constant bias current – runs continuously (e.g. even without signal)– (Nominally) constant gm, pole frequencies– Poor power efficiency

• Class B– Bias current matches signal amplitude– No current when signal amplitude is zero– Usually high distortion

• Class AB– Class B with (small) quiescent current continuously running– Reduced distortion (compared to class B)– Used in output stages and buffers

• Class D– PWM “digital” output– Very high power efficiency– E.g. audio amplifiers

• …

EE240B – Biasing

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