Phase Noise and Oscillators

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# Phase Noise and Oscillators - PowerPoint PPT Presentation

Phase Noise and Oscillators. Stephen Powell. What is an Oscillator?. Produces a signal at a particular frequency They are everywhere! watches, radios, computers, in most electronic circuits Uses? Generates signals for transmission Frequency translation Provides timing references.

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## PowerPoint Slideshow about 'Phase Noise and Oscillators' - shelley-hardin

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### Phase Noise and Oscillators

Stephen Powell

What is an Oscillator?
• Produces a signal at a particular frequency
• They are everywhere!
• watches, radios, computers, in most electronic circuits
• Uses?
• Generates signals for transmission
• Frequency translation
• Provides timing references
How to build an Oscillator!
• Need a feedback loop
• Oscillates at frequency ω0 when

1-A(jω0)B(jω0) = 0 (Barkhausen criteria)

• Unstable device!
L,C,R forms an impedance “tank”

Impedance has same form as the loop equation

Voltage across tank oscillates

Simple LCR Oscillator
Effect of Resistance

Without R

With R

Phase Noise
• Oscillator output: V(t) = C·sin(ω0t+θ(t))
• Suppose θ(t) = θsin(pt) model one component of white noise… then:
Origins of Phase Noise
• Three types of contributing noise:
• Flicker Noise: power inversely proportional to frequency, AKA 1/f noise
• Shot Noise: due to random charge carriers, proportional to current
• Thermal Noise: present in all resistors, wide band, AKA Johnson noise
Aggregate Phase Noise
• All three types together…

ω1/f3

log(L(∆ω))

ω0/2Q

Shot Noise

Thermal Noise

Flicker Noise

log(∆ω)

Modified Leeson Model
• Tries to account for traits seen in spectrum
• Loosely based on principle of time-invariance
• F, ω1/f3 are empirically calculated
• Not good for prediction!
Lee Model
• Based on time-variance
• No empirical variables
• Corresponds well to observations
Lee Model (continued)…

Region of 1/f3

(Flicker Noise)

Region of 1/f2

(Shot Noise)

Effects of Phase Noise
• In the time domain: Timing Jitter
• bad if you want to synchronize a signal, or sample a signal

Effects of Phase Noise…

• In the frequency domain: Reciprocal Mixing