As the SX device can operate at frequencies up to 75 MHz, are there recommendations for proper oscillator circuit layout to minimize EMI?
It is typically recommended to reduce the power and ground loop area. The long supply lines with the relatively large areas that these lines surround may form an effective antenna. At the frequencies present, an unacceptable level of interference may be radiated and may result in unstable oscillation. A grounded area under the SX device must be connected to the Vss pin. In addition, the ground area should be tied to the ground plain with multiple vias. This ground area ensures that the major part of the field lines emanating from the SX are concentrated between the SX and the ground level. Since the SX28AC power and ground pins are on the opposite side of the package from the one for the oscillator pins, one needs to evaluate the effect of the larger loop created as a result of connecting the oscillator capacitors to the ground. This large loop will result in larger amount of current flow in the oscillator resonant circuit. The creation of a ground plane underneath the chip (mentioned
