Integration Manual

TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R26 Design-in
Page 118 of 162
 Cross other signals lines on adjacent layers with 90° crossing.
 Place bypass capacitor for RF very close to active microphone. The preferred microphone should be designed
for GSM applications which typically have internal built-in bypass capacitor for RF very close to active device.
If the integrated FET detects the RF burst, the resulting DC level will be in the pass-band of the audio circuitry
and cannot be filtered by any other device.
General guidelines for the downlink path (speaker / receiver) are the following:
 The physical width of the audio output lines on the application board must be wide enough to minimize series
resistance since the lines are connected to low impedance speaker transducer.
 Avoid coupling of any noisy signal to speaker lines: it is recommended to route speaker lines away from
module VCC supply line, any switching regulator line, RF antenna lines, digital lines and any other possible
noise source.
 Avoid coupling between speaker / receiver and microphone lines.
 Optimize the mechanical design of the application device, the position, orientation and mechanical fixing (for
example, using rubber gaskets) of speaker and microphone parts in order to avoid echo interference between
downlink path and uplink path.
 In case of external audio device providing differential speaker / receiver output, route speaker signal lines as a
differential pair embedded in ground up to reduce differential noise pick-up. The balanced configuration will
help reject the common mode noise.
 Cross other signals lines on adjacent layers with 90° crossing.
 Place bypass capacitor for RF close to the speaker.