xtal orientation

[Simon]

On PCB layouts I often see that the HF xtal is oriented at 45 degrees relative to the orientation of the 51x chip (that is to say the edges of the the xtal and 51x chips are not parallel). And in the Crystal Oscillator Design Considerations white paper it states: “The parasitic capacitances found on the PCB must be made as equal as possible through symmetrical PCB routing.”

So I’m guessing this “45 degree” orientation is how the symmetry is achieved. If so then what is symmetrical? Or is it just about ease of routing?

[Håkon Alseth]

Hi Simon,

It's angled at 45 degrees to make the whole circuitry smaller in size. The PCB tracing to the XTAL is usually always symmetrical, as most people place the XTAL close to the chip. The section in the white paper is more related to designs where the xtal is placed away from the chip (clock sharing for instance)

By symmetrical, we mean that you route the XC1 and XC2 lines parallel to each other.

Best regards Håkon