LEON-G100 / LEON-G200 - System Integration Manual
GSM.G1-HW-09002-G3
Preliminary
Design-In
Page 88 of 125
Avoid coupling of any noisy signals to microphone inputs lines
It is strongly recommended to route MIC signals away from battery and RF antenna lines. Try to skip fast
switching digital lines as well
Keep ground separation from other noisy signals. Use an intermediate GND layer or vias wall for coplanar
signals
MIC_BIAS
and
MIC_GND
carry also the bias for external electret active microphone. Verify that microphone
is connected with right polarity, i.e.
MIC_BIAS
to the pin marked “+” and
MIC_GND
(zero Volt) to the
chassis of the device
Despite different DC level,
MIC_BIAS
and
MIC_GND
are sensed differentially within the module. Therefore
they should be routed as a differential pair of
MIC_BIAS
up to the active microphone
Route
MIC_GND
with dedicated line together with
MIC_BIAS
up to active microphone.
MIC_GND
is
grounded internally within module and does not need external connection to GND
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
If DC decoupling is required, consider that the input impedance of microphone lines is in the k
Ω
range.
Therefore, series capacitors with sufficiently large value to reduce the high-pass cut-off frequency of the
equivalent high-pass RC filter
Output audio lines have two separated configurations.
SPK_P
/
SPK_N
are high level balanced output. They are DC coupled and must be used with a speaker
connected in bridge configuration
Route
SPK_P
/
SPK_N
as differential pair, to reduce differential noise pick-up. The balanced configuration
will help reject the common mode noise
If audio output is directly connected to speaker transducer, given the low load impedance of its load, then
consider enlarging PCB lines to reduce series resistive losses
HS_P
is single ended analog audio referenced to GND. Reduce coupling with noisy lines as this Audio
output line does not benefit from common mode noise rejection of
SPK_P
/
SPK_N
Use twisted pair cable for balanced audio usage, shielded cable for unbalanced connection to speaker
If DC decoupling is required, a large capacitor needs to be used, typically in the µF range, depending on the
load impedance, in order not to increase the lower cut-off frequency due to its High-Pass RC filter response
2.2.1.4
Module grounding
Good connection of the module with application board solid ground layer is required for correct RF
performance. It significantly reduces EMC issues and provides a thermal heat sink for the module.
Connect each
GND
pin with application board solid GND layer. It is strongly recommended that each
GND
pad surrounding
VCC
and
ANT
pins have one or more dedicated via down to application board solid ground
layer. The same applies to
GND
pins on the opposite side close to charger pins
If the application board is a multilayer PCB, then it is required to tight together each GND area with
complete via stack down to main board ground layer
It is recommended to implement one layer of the application board as ground plane
Good grounding of
GND
pads will also ensure thermal heat sink. This is critical during call connection, when
the real network commands the module to transmit at maximum power: proper grounding helps prevent
module overheating
