10.1.1 PCB Layout

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 ADC141S628-Q1 because of supply noise, avoid using the same supply for the V_A and V_REF of the ADC141S628-Q1 that is used for digital circuitry on the board.

Generally, analog and digital lines must 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 also 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.

A single, uniform ground plane and the use of split power planes are recommended. Place the power planes within the same board layer. All analog circuitry (input amplifiers, filters, reference components, and so forth) must be placed over the analog power plane. Place all digital circuitry over the digital power plane. Furthermore, the GND pins on the ADC141S628-Q1 and all the components in the reference circuitry and input signal chain that are connected to ground must be connected to the ground plane at a quiet point. Avoid connecting these points too close to the ground point of a microprocessor, microcontroller, digital signal processor, or other high power digital device.