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: =122 pS, Delay per stage (T D ): =20 pS. Period is 2NT D

Oscillation Frequency Calculation f osc =2.14 GHz T osc =467 pS=2NT D – T D =20 pS – N=T osc /(2T D )=467 pS/(2 20)=11.68 – N must be odd. – Choose N as 11.

11 Stage Oscillator

Period: nS 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 g tank is greater than g m of the transistor.

R ind =100 mΩ This is the maximum parasitic resistance we can have without destroying the oscillation.

Transient Simulation

Phase Noise with R ind =100 mΩ Even a little series resistance at unreasonably high Q (130) can degrade phase noise quickly.