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Jul 10th, 2020, 7:29pm
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Is coupling between on-chip inductors a real issue? (Read 426 times)
Horror Vacui
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Is coupling between on-chip inductors a real issue?
Oct 14th, 2019, 2:52am
 
I've had a discourse with a more senior engineer where he meant that on-chip inductors are not a threat, they are used in mobile phone for 25+ years, and the only reason why an inductorless circuit is preferred for similar performance is the reduced area. On the other hand I fear that we can not so easily dismiss any coupling between the inductors, and even in the presence of a ground plane they could introduce spurs, pulling or shift the DC bias by down-convertion on non-linearities.

If any of you worked on such chips, could share how much trouble did those inductors caused for you? Does the system architect live in a constant paranoia about the possible sources of spurs, or these can be kept within limits required by the strict emission standards by good engineering practices. In the latter case - I guess - the main mischief makers are the IR drops, substrate coupling, conducted interference on the bias and reference lines.
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subtr
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Re: Is coupling between on-chip inductors a real issue?
Reply #1 - Nov 18th, 2019, 11:00pm
 
It's a problem when it comes to jitter causing BER's in transceivers. The if two oscillators are coupling, then it can cause injection locking or at least spurious tones. Keeping the inductors far as possible is the solution plus maybe 8 shaped or clover shaped inductor helps to prevent inducing fields far away as well as rejecting fields. This is nothing different from using twisted pair cables in our systems for transmitting signals without getting affected by magnetic interference.
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Regards
Subtr
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smlogan
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Re: Is coupling between on-chip inductors a real issue?
Reply #2 - Jan 17th, 2020, 3:40pm
 
Dear subtr and Horror,

Coupling between on-chip inductors can be a very significant problem as I have had multiple experiences concerning on-chip inductors used in LC based VCO. There are multiple papers addressing the issue. Proximity is an issue, but the magnetic fields fall off rapidly and hence increasing spacing between on-chip inductors is of limited use if you are experiencing significant coupling. However, the source of the coupling is also related to the non-linear nature of the varactors of the VCO and coupling that is introduced to them. Hence, the effect is not one of only inductor to inductor coupling. It can also be related to numerous coupling sources into LC based VCO varactors. In my experience, extremely careful layout and experience with this type of interaction is necessary to avoid significant coupling.

Shawn
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Shawn
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reneezl_rex
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Re: Is coupling between on-chip inductors a real issue?
Reply #3 - Jan 26th, 2020, 9:38am
 
Hello smlogan,

Could you please share the name of the papers? I am working on reducing the coupling between on-chip inductors or transmisson lines. Thanks.

Best regards,

Renee
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