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Design >> Analog Design >> Ring Oscillator Pre vs. Post Layout Frequency Shift
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Message started by melvin1109 on Nov 25th, 2019, 3:29pm

Title: Ring Oscillator Pre vs. Post Layout Frequency Shift
Post by melvin1109 on Nov 25th, 2019, 3:29pm

Hello All,

I am trying to layout a ring oscillator that oscillates at ~300MHz in pre layout simulations. The issue I am having is that in post layout simulations the oscillation frequency is ~100MHz.

This is my first layout, so I do not know any good layout practices for this frequency range.

I assume that propagation delay is being increased becasue various parasitic resistances/capacitances in the layout.

Can you guys suggest some things I can look at in my layout, in general, that I could tweak in order to reduce parasitics and bring my post layout frequency closer to my pre layout frequency?

Also, what are things are typically the biggest contributors to a shift in frequency when laying out oscillators?

Thanks

Title: Re: Ring Oscillator Pre vs. Post Layout Frequency Shift
Post by kumar.g on Dec 3rd, 2019, 4:59am

The layout parasitics can not increase the RC time constant by 300% unless it is done in a complete amateurish way. You can search it on the web and you will find general guidelines to do a proper layout.

Title: Re: Ring Oscillator Pre vs. Post Layout Frequency Shift
Post by Maks on Dec 7th, 2019, 1:58pm

This shift is most likely caused by layout parasitics.

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