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Amin ArbabianJan M. Rabaey

Lecture 25Negative Resistance View, Oscillator Circuits

EE142 – Fall 2010

Nov. 30th, 2010

University of California, Berkeley

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Review

Analyzed amplitude limiting mechanisms and steady-state oscillation conditions

Amplitude stability

Life-cycle of an oscillator going to start-up, amplitude limitations and finally stable output

Today: Negative resistance view of oscillators, differential oscillators, VCOs and crystal oscillators.

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Negative Resistance Perspective

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Oscillator Stability

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Negative Resistance LC Oscillator

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Oscillation Condition

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One-Port View of a General Oscillator

Bias not shown

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Colpitts Oscillator

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Colpitts Oscillator (2)

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Clapp Oscillator

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Clapp Oscillator (2)

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MOS Oscillators

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Differential Oscillators

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Negative Conductance of Cross-Coupled Pair

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Cross-Coupled Oscillator

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Other MOS Differential Oscillators

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BJT Differential Oscillator

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Virtual Ground

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Voltage-Controlled Oscillators

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PN Junction Varactors

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Doping Profile

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Varactor-Tuned LC Oscillator

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Clapp VCO

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Varactor-Tuned Differential Oscillator

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Varactor-Tuned Differential Oscillator (2)

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MOS Varactors

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MOS Varactors (2)

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Accumulation Mode MOS Varactors (A-MOS)

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Switched Capacitor Varactors

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Crystal Oscillators

The piezoelectric crystal is an electro-mechanical device with a sharp frequency selective response.

Equivalent Q > 10,000 are available.

The piezoelectric material exhibits a transduction between mechanical strain and electric charge.

Very good stability and low temperature coefficient.

Example:f=1.59 MHz (series)R = 125 Ω, L = 250 mH, C = 40 fF, Co = 4 pF

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Crystal Oscillators