SLLSEA9B February 2012 – August 2015 SN75DP126
PRODUCTION DATA.
Digital ground and power carry the RF energy that needs to be contained, so it is best to isolate it from any other power and ground, either analog, high power, or other unrelated trace. If noise from the microcomputer or any other circuit gets on an isolated ground, it can be returned by careful placement of a small RF capacitor in the 470 – 1000 pF range. Choosing the location of the capacitor is by trial and error, and is best done in the screen room.
The reference voltage of an analog-to-digital (A/D) converter integrated into a microcomputer does supply a very small amount of clocked current; however, it is not enough to be concerned about from a noise-emissions standpoint. Most applications have the analog VSS /VCC tied to the digital VSS1 /VCC1 pins, which does not change significantly the noise characteristics of the A/D nor the radiated emissions