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High speed diff pair trace swap

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Newbie level 2
Feb 17, 2013
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I am placing a active mixer and a frequency agile PLL onto a piece of FR4 (1.6mm) – I know this isn’t a great material to use for this.

To do this I want to get the two ICs as close together as possible to minimise the nasty effects of this material, and minimise the need to do microstrip/transmission line matching

The two ICs will have a maximum frequency of 2.5GHz from the PLL to the mixer, and it’s a differential connection

My issue is, the positive and negatives of the differential pair are in the same position on the two ICs, connecting them together thus isn’t nice and clean, so im left with 3 options as I see it:

1) Route one of the connections through the middle of a AC coupling cap (0402 – not much room) to change its position, and maybe try and lengthen the other track to suit
2) Pop a couple of VIAs down and cross the tracks on the bottom layer with one of the traces
3) Connect the positive from one IC to the negative on the other and vice versa for the other differential pin

I would really appreciate some recommendations and opinions concerning this,

Many thanks

I would select the 3rd option. It seems not matter to link LO plus and negative.
I would select the 3rd option. It seems not matter to link LO plus and negative.

Yes i was hoping this, i also noticed the datasheet of the mixer suggesting using a balun there for optimal performance, so i may do this at that point

Many thanks

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