Capacitive coupling between the noisy digital circuitry and the sensitive analog circuitry can lead to poor performance. The solution is to keep the analog circuitry separated from the digital circuitry and the clock line as short as possible.

Digital circuits create substantial supply and ground current transients. The logic noise generated can have significant impact upon system noise performance. To avoid performance degradation of the ADC128S102-SEP resulting from supply noise, do not use the same supply for the ADC128S102-SEP that is used for digital logic.

Generally, analog and digital lines cross each other at 90° to avoid crosstalk. However, to maximize accuracy in high-resolution systems, avoid crossing analog and digital lines altogether. Clock lines must be kept as short as possible and isolated from all other lines, including other digital lines. In addition, the clock line must be treated as a transmission line and be properly terminated.

Isolate the analog input from noisy signal traces to avoid coupling of spurious signals into the input. Any external component (for example, a filter capacitor) connected between the converter input pins and ground or to the reference input pin and ground must be connected to a very clean point in the ground plane.

Use a single, uniform ground plane and split power planes. The power planes must be located within the same board layer. Place all analog circuitry (input amplifiers, filters, reference components, and so forth) over the analog power plane. Place all digital circuitry and I/O lines over the digital power plane. Furthermore, all components in the reference circuitry and the input signal chain that are connected to ground must be connected together with short traces and enter the analog ground plane at a single, quiet point.