SC14WAMDECT datasheet(25/36 Pages) DIALOG

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Datasheet

Revision 3.0

23-Jul-2015

CFR0011-120-00-FM Rev 5

25 of 36

SC14WAMDECT SF

Wireless Audio Module

FINAL

7.0 Design guidelines

7.1 PCB DESIGN GUIDELINES

• Because of the presence of the digital radio fre-

quency bursts with 100 Hz time division periods

(TDD noise), supply ripple and RF radiation, special

attention is needed for the power supply and ground

PCB layout.

• Power supply considerations

Both high and low frequency bypassing of the supply

line connections should be provided and placed as

close as possible to the SC14WAMDECT SF. In

order to get the best overall performance for both FP

and PP applications, a number of considerations for

the PCB has to be taken into account.

• Make angle breaks on long supply lines to avoid

resonances at DECT frequencies. Maximum

80 mm before an angle break is recommended.

• Supply lines should be placed as far as possible

away from sensitive audio circuits. If it is neces-

sary to cross supply lines and audio lines, it

should be done with right angles between supply

and audio lines/circuits (microphone, ear-speaker,

speakerphone, etc.)

• Ground plane considerations

In order to achieve the best audio performance

and to avoid the influence of power supply noise,

RF radiation, TDD noise and other noise sources,

it is important that the audio circuits on both FP

and PP applications boards are connected to the

VREFm pin on the SC14WAMDECT SF with sep-

arate nets in the layout.

It is advised to provide the following audio circuits

with separate ground nets connected to the

VREFm pin:

• Microphone(s)

• Headset microphone and speaker

• Speakerphone (signal grounds)

Depending on the layout it may also be necessary to

bypass a number of the audio signals listed above to

avoid humming, noise from RF radiation and TDD

noise. It is also important to choose a microphone of

appropriate quality with a high RF immunity (with built-

in capacitor).

• ESD performance

Besides TDD noise, the ESD performance is impor-

tant for the end application. In order to achieve a

high ESD performance, supply lines should be

placed with a large distance from charging terminals,

display, headset connector and other electrical ter-

minals with direct contact to the ESD source.

On a two-layer PCB application it is important to

keep a simulated one layer ground. With a stable

ground the ESD and TDD noise performance will

always improve.

• Clearance around test patterns

Pins 81 to 88 are used for production test purposes.

In order to avoid any interference or disturbance the

area around these signal pins must be kept clear of

any signal and/or GND. The recommended clear-

ance is at least 1 mm, as shown in Figure 13.

7.2 MODULE PLACEMENT ON THE MAIN BOARD

In order to ensure FCC compliance, proper coverage

and to avoid detuning of the antennas, it is required to

place the module on the main board free from other

surrounding materials.

Keep a distance of at least 10 mm from the antenna

elements to conducting objects and at least 5 mm to

non-conducting objects.

Keep in mind that electrically shielding objects, even

partly surrounding the antennas, will normally cause a

significant degradation of the coverage.

Place the module at the edge of the main-board as

shown in Figure 14.

When the module has to be placed away from the edge

of the main board, avoid any conducting areas in front

of the antennas and make a cut-out in the main board

underneath the antennas as shown in the figure.

See Figure 18 and Figure 21 for the detailed package

outline.

Figure 13: Clearance around test patterns

Test

pattern

0.9 mm

1.0 mm

GND Pattern

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