AD7863

Rev. B | Page 20 of 24

APPLICATIONS HINTS

PC BOARD LAYOUT CONSIDERATIONS

The AD7863 is optimally designed for lowest noise performance,

both radiated and conducted noise. To complement the

excellent noise performance of the AD7863 it is imperative that

great care be given to the PC board layout. Figure 26 shows a

recommended connection diagram for the AD7863.

GROUND PLANES

The AD7863 and associated analog circuitry should have a

separate ground plane, referred to as the analog ground plane

(AGND). This analog ground plane should encompass all

AD7863 ground pins (including the DGND pin), voltage

reference circuitry, power supply bypass circuitry, the analog

input traces, and any associated input/buffer amplifiers.

The regular PCB ground plane (referred to as the DGND for

this discussion) area should encompass all digital signal traces,

excluding the ground pins, leading up to the AD7863.

POWER PLANES

The PC board layout should have two distinct power planes,

one for analog circuitry and one for digital circuitry. The analog

associated analog circuitry. This power plane should be

point, if necessary through a ferrite bead, as illustrated in

Figure 26. This bead (part numbers for reference:

Fair-Rite 274300111 or Murata BL01/02/03) should be located

within three inches of the AD7863.

provide power to all AD7863 power pins, voltage reference

circuitry and any input amplifiers, if needed. A suitable low

noise amplifier for the AD7863 is the AD797, one for each

amplifier are individually decoupled to AGND.

to a reduction in plane-to-plane noise coupling.

SUPPLY DECOUPLING

by use of multiple decoupling capacitors (Figure 26).

Optimum performance is achieved by the use of disc ceramic

external or an internal reference) should be individually

decoupled to the analog ground plane (AGND). This should be

done by placing the capacitors as close as possible to the

AD7863 pins with the capacitor leads as short as possible, thus

minimizing lead inductance.

AD7863

AGND

DGND

AGND

AD780

L

(FERRITE BEAD)

TEMP

+15V

0.1µF

0.1µF

0.1µF

0.1µF

10µF

47µF

ANALOG

SUPPLY

+5V

ANALOG

SUPPLY

–15V

0.1µF

4 × AD797s

0.1µF

Figure 26. Typical Connections Diagram Including the Relevant Decoupling