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Electronics => Beginners => Topic started by: Vcky_electro on July 25, 2019, 03:30:26 pm

Title: Analog trace width discontinuity but same impedance.
Post by: Vcky_electro on July 25, 2019, 03:30:26 pm

Hi,
I'm using GPS SMA connector with 50oHM trace as shown in the image. Where the trace width is very tiny compared to the SMA connecter's pad . What my doubt is, will the tiny trace width affect the signal flow ?? my thought is the trace width need to be same as the pad width for the flow will be better and VSWR will be better. is my understanding correct ?? if i do like that i cant achieve 50 ohms. so what would i do ??

Awaiting for anyones reply..

Thanks .
Vicky

Title: Re: Analog trace width discontinuity but same impedance.
Post by: eb4fbz on July 25, 2019, 03:47:22 pm

You should remove GND plane underneath the connector pad to compensate that. However look at the SMD components too! Their pads are very big compared to the 50ohm line. Maybe you should change board stackup.

Title: Re: Analog trace width discontinuity but same impedance.
Post by: T3sl4co1l on July 25, 2019, 04:22:18 pm

Neither is a huge problem at λ/4 ~ 70mm.  The change in transmission line impedance is modest, and the length is short compared to the wavelength.

The pads may be interesting in their effect on detuning a filter, if present.  As mentioned, they are quite large relative to the trace width.

No stitching vias?

Tim

Title: Re: Analog trace width discontinuity but same impedance.
Post by: Mechatrommer on July 25, 2019, 06:00:31 pm

Quote from: eb4fbz on July 25, 2019, 03:47:22 pm

You should remove GND plane underneath the connector pad to compensate that.

i think thats to reduce capacitance? hi-freq + a capacitance = LPF? (disclaimer = i'm not the expert)