How to match the impedance of analog circuit signal trace?

[EDA_hg81]

Should I use the same way used for digital circuit signal trace to match the impedance of analog circuit signal trace?

Can the impedance of analog circuit signal trace be tuned by PCB layout?

Do we have an easy way to decide the values of terminating impedance components (such as Cap and resistors) based on frequency?

:?::|

 

[FvM]

You should worry about impedance matching of analog signal traces with bandwiths above 50 or 100 MHz. Is this your application?

For high speed analog, basically the same techniques of impedance matching apply as for digital, but the requirements are ussually much tighter, depending on the intended analog resolution.

I don't see however, how a capacitor can be used to terminate a real transmission line impedance.

 

[EDA_hg81]

Re: How to match the impedance of analog circuit signal trac

You are right; my application is about 60MHZ.

Please check this, they use cap and resistor for termination.

Do you have any reference about analog termination requirements?

Should I only check the rise time for deciding if termination has to be implemented?

Thanks.

 

[dick_freebird]

I don't think the 47p, 100 ohm leg is strictly a termination.
The corner frequency is pretty high, greater than your fundamental,
so the termination impedance is still frequency dependent
and that's not a good thing. I think probably it's more of an
attempt to kill edge harmonics, short-line reflections or something
of that sort. It looks to me like maybe the cap / shield combo is
trying to generate a resonance or a peaking, and the RC then tries
to scrub off some of the higher frequency "modes". Or something.