Rainbow Electronics ADC12041 - Manual (Page 27)

Analog Application Information
(Continued)
TL H 12441 – 45
FIGURE 10 Top View of Printed Circuit Board for a 28-Pin PLCC ADC12041
When measuring AC input signals any crosstalk between
analog input lines and the reference lines (ADCIN
g
V
REF g ) should be minimized Crosstalk is minimized by re-
ducing any stray capacitance between the lines This can be
done by increasing the clearance between traces keeping
the traces as short as possible shielding traces from each
other by placing them on different sides of the AGND plane
or running AGND traces between them
Figure 10 also shows the reference input bypass capacitors
Here the reference inputs are considered to be differential
The performance improves by having a 0 1 mF capacitor
between the V REF a and V REF b and by bypassing in a
manner similar to that described for the supply pins When a
single ended reference is used V
REF
b is connected to
AGND and only two capacitors are used between V
REF
a
and V REF b (0 1 mF a 10 mF) It is recommended to directly
connect the AGND side of these capacitors to the V REF b
instead of connecting V REF b and the ground sides of the
capacitors separately to the ground planes This provides a
significantly lower-impedance connection when using sur-
face mount technology
27