Electronic – differential grounded coplanar waveguide, GND-sig-sig-AVDD instead of GND-sig-sig-GND

differentialpcb-designRF

I know we can route microstrips on top of both ground and power planes, but can we use Grounded coplanar in this arrangement?

  • bottom is GND
  • In top layer we have one GND and a PWR.
  • All gaps are 0.15mm
  • Working frequency: 12GHz

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1.Will it damage integrity of signal? Why?

2.(The question has been added refering to marcus mullers comments) I've used this design because Analog Devices has used it on his own reference design. But will it advantageous since the field will confine in between two microstrip. (I think it helps at least to prevent field to propagate through PCB material.) And will Differential GCPW cost of design worth it to switch to it from simple microstrip?

Analog devices reference design:

1.UG-864:
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2.UG-866:
enter image description here

Best Answer

My main concern would be that each VCC via will produce an antipad in the ground plane, making the geometry asymmetric.

Ideally the traces in the differential pair only interact with each other, as another answer said. But practically (especially in a dense design like your example), they also interact with surrounding conductors, and the coplanar ground, or ground beneath a differential microstrip will affect the characteristic impedance. And discontinuities in the ground will cause reflections and/or mode conversion in the propagating signals.

So one trace having ground directly beneath it, and the other having ground with periodic gaps due to the VCC vias, is likely to produce undesirable results, such as a different characteristic impedance than expected or differential-to-single-ended signal conversion.

I'd try to find an alternative geometry. Either differential microstrip, or coplanar with ground on both sides.

I believe both of the examples you showed from Analog Devices documentation show CPWG with ground on both sides. Neither one shows a power net being used as ground like you propose.

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