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.