AS3435 datasheet(87/102 Pages) AMSCO

87 / 102 page

ams Datasheet, Confidential: 2014-Jun-13 [v1-30]

AS3415/AS3435 – 87

P C B La y o ut Recommendation

Microphone

For the microphone preamplifier layout the designer must pay

special attention; the combination of bad layout and gain

values up to +20dB can cause unwanted noise. To minimize

noise, a layout example is shown in Figure 108 which is based

on the schematic shown in Figure 20. All microphone related

components which include DC blocking capacitors, bias

resistors as well as high pass filter components should be placed

according to Figure 108. Once the component placement is

done it is important to route the different ground connections

of all components correctly. For the microphone preamplifier a

local star shaped ground concept should be used, with AGND

pin defined as star point. Basically we have two important

ground pairs. The first are the microphone grounds next to MICR

and MICL terminals. These ground pins need a separate ground

connection back to the AS3515/35 AGND pin. A separate left

and right ground line is recommended rather than using a

single microphone ground line back to the star point at AGND.

The second important connections are the ground terminals of

CAC and RMICIN. They should be fed back to the AGND pin.

Figure 108 shows the separation of left and right channel. The

ground pads of CAC and RMICIN are connected together and

routed back to AGND pin of AS3415/35.

Figure 108:

Microphone Layout Recommendation

AS3415/35 Microphone Layout Recommendation: This diagram shows the layout recommendation for the

AS3415/35 microphone preamplifier with all necessary peripheral components for operation.

Microphone Ground Layout:

Use separate ground connections for microphone inputs back to the AGND pin. The ground connection of CAC

and RMICIN should also make use of a dedicated connection back to AGND pin of AS3415/35.

BIAS

TOP LAYER

SILK SCREEN TOP LAYER

BOARD OUTLINE

BOTTOM LAYER

AGND

AS3435

Connection to negative

battery terminal

COMMENT LAYER

Combined CAC and RMICIN

ground back to AGND pin.

Microphone ground

terminal left microphone

Microphone ground

terminal right microphone

Star point for microphone

ground connection

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