Question
What are some common guarding techniques?
Answer
Guarding is important to completely surround the insulation of the high impedance node with another conductor that is driven to the guard voltage. Afew practical structures can be implemented at the board level to provide good performance. A guard ring is a structure typically used to implementguarding technique on the surface of a PCB. A filled copper shape ring completely surrounds the high impedance trace to avoid surface leakage. Aguard plane is another structure to guard leakages through the bulk of the PCB. Place the guard plane directly below the high impedance trace. Thisplane is then connected to the guard ring on the surface layer with vias. A via fence can also guard the lateral leakage paths in the laminatebetween the guard ring and the guard plane. Surround the entire guard ring with vias that connect the guard ring to the guard planes. Forillustrations, refer the ADA4530-1 data sheet.
