ADL5303 Layout

Question

Hello, 
 
 I'm designing a circuit with ADL5303 . The datasheet suggests to guard the INPT trace with guard traces which are connected to VSUM, and i guess (as it not shared in the datasheet) that these guard traces are connected with vias to layer2, to reduce leakage. 
 My concern is, won't these guard traces act as an antenna and pick-up noise? 
 I've also read in a similar thread about ADL5304 that a grounded shield may be needed above the trace. Is it grounded or also attached to these traces? As if it is grounded, what about the leakage to GND in that case, isn't it what we wanted to eliminate in the first place? 
 
 Thanks

EZAutoReply · Accepted Answer

Hello,

A shield is only recommended for low input currents i.e currents lower than 1 nA. The guard traces are at the same potential as input trace and layer 2 is connected to guard potential to minimize leakage. Unlike RF boards the input impedance of the input trace is high and input capacitance is low. The extra vias along the guard trace also reduce the magnetic field pick up i.e the noise is reduced through the ground vias between layer 1 and layer 2.

Thanks.

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