Phase Noise in LC Oscillators

1
Phase Noise in LC Oscillators

• Henry C. Jen
• Robert G. Meyer
• January 2001

2
Practical Oscillator
On scope

• finite
• stable

3
Phase Noise Analysis
Positive feedback amplifier

• cf Leesons equation
• cyclostationarity
• 1/f mixing

4
Startup in Ideal Oscillator

• no noise sources in oscillator
• started by impulse excitation (glitch)
• amplitude builds up without any noise
• verified with transient simulation

5
Startup in Practical Oscillator

• noise sources in oscillator
• oscillator in linear mode
• output consists of main tone plus noise
• difficult to verify with simulation

6
Phase Noise during Startup
Phase noise much lower during startup!
7
Simulation Problems

• Difficult quasi-steady state
• SpectreRFs PSS analysis doesnt work
• working with Cadence to resolve issues
• Transient runs in time domain
• Modeling of thermal and 1/f noise
• tones in frequency domain
• random numbers in time domain
• Monte-Carlo analysis in SIMULINK

8
Simulation Results

• phase noise lowered, especially close-in
• 1/f corner shifted lower
• trend matches measurements from discrete prototype

9
Future Work

• Complete characterization of prototype
• Verify theory against measurements
• Design a 1-GHz VCO operating in linear mode and
  fabricate in 0.18-?m CMOS
• Continue working with Cadence to resolve
  simulation problems in SpectreRF