Regarding 1 rule of RF devices-

[gunjang]

Hi,
Can anyone explain the following rule -
Never do common centroid matching for RF devices. Merge implant & diffusion of devices where possible (like the common source differential transistors) & double feed gate poly from both the side.
My question is - why common centroid matching is avoided for RF devices?

 

[jiesteve]

Probably because the extra routing required for common centroid matching adds too much capacitance and kills the bandwidth.