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Reference Spur in Injection Locked Oscillator (Read 1209 times)

sarthak

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Reference Spur in Injection Locked Oscillator
Apr 13^th, 2018, 8:50am

Hello,
I am trying to simulate injection locked ring oscillator, where the injection signal is ideal pulse wave generated using "vsource" whose pulse width is To/4, where To is the time period of the ring oscillator. For the injection switch I am using ideal switch.
But in the DFT plot of the output I am getting lot of reference spurs even though I have set the free running frequency of the ring oscillator very close to the injection harmonic frequency (40th harmonic for my case).
Could someone point out a possible reason for the high reference spur? The following are my simulation conditions:
Oscillator Free running frequency = 2.5600016GHz (Error Frequency = 1.6kHz)
Injection Frequency = 64MHz
Reference Spur = -51dB

Spur.PNG

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deba

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Re: Reference Spur in Injection Locked Oscillator
Reply #1 - Apr 13^th, 2018, 11:55pm

Injection locking clock source will have high reference spurs. This is due to the periodic injection of the reference signal. The phase of the free running oscillator will always drift, and the injection signal will bring it back. Thus, causing a reference spur.

This is an open problem and lot of techniques like MDLL, alignment PLLs are available to solve the reference spur issue. Look up IEEE.

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