Data Sheet
AD823A
MAXIMIZING PERFORMANCE THROUGH PROPER
LAYOUT
V
V
OUT
OUT
V
IN
V
To achieve the maximum performance of the extremely high
input impedance and low offset voltage of the AD823A, care
should be taken in the circuit board layout. The PCB surface
must remain clean and free of moisture to avoid leakage currents
between adjacent traces. Surface coating of the circuit board
reduces surface moisture and provides a humidity barrier, reducing
parasitic resistance on the board. The use of guard rings around the
amplifier inputs further reduces leakage currents. Figure 48 shows
how the guard rings should be configured, and Figure 49 shows
the top view of how a surface-mount layout can be arranged. The
guard ring does not need to be a specific width, but it should form
a continuous loop around both inputs. By setting the guard ring
voltage equal to the voltage at the non-inverting input, parasitic
capacitance is minimized as well. For further reduction of leakage
currents, components can be mounted to the PCB using Teflon®
standoff insulators.
IN
AD823A
AD823A
V
IN
V
OUT
AD823A
Figure 48. Guard Ring Layout and Connections to
Reduce PCB Leakage Currents
V+
R1
R2
AD823A
R2
R1
V
IN1
V
IN2
GUARD
RING
GUARD
RING
V
REF
V
REF
V–
Figure 49. Top View of AD823A SOIC Layout with Guard Rings
Rev.B | Page 19 of 20