Oscillator Circuits

Outline

• Oscillators– Inverter-Based Oscillator– Introduction of Phase Noise Simulation– LC-Tank Based Oscillator• Laplace Analysis• Circuit Implementation• Quality Factor Analysis

Inverter-Based Oscillator

Delay Per Stage of the Inverter(273 pS) (395 ps)

Period: 395-273=122 pS, Delay per stage (TD): 234-214=20 pS. Period is 2NTD

Oscillation Frequency Calculation

• fosc=2.14 GHz

• Tosc=467 pS=2NTD

– TD=20 pS

– N=Tosc/(2TD)=467 pS/(2 20)=11.68

– N must be odd. – Choose N as 11.

11 Stage Oscillator

11 Stage Oscillator

Period: 1.501 nS-1.052 nS=0.449 nS, Freq=2.227 GHz

Phase Noise

Periodic Steady State Analysis

Harmonics

Pnoise

Phase Noise of a Ring Oscillator

LC Tank Oscillator

Laplace Transform Analysis

LC Tank Oscillator

• Resonant Frequency: 2.14 GHz• L=1 nH• C=5.53 pF (Adjustable)

LC Tank Oscillator

Transient Simulation

(Steady state after 10 nS)

Frequency: 1.941GHz

Reduce the Value of Capacitor

(2.16 GHz)

PSS and Pnoise Setting

Phase Noise

Quality Factor of 10 for the inductor

Oscillation dies out since gtank is greater than gm of the transistor.

Rind=100 mΩ

This is the maximum parasitic resistance we can have without destroying the oscillation.

Transient Simulation

Phase Noise with Rind=100 mΩ

Even a little series resistance at unreasonably high Q (130) can degrade phase noise quickly.