User's Manual

LISA-U1/LISA-H1 series - System Integration Manual
3G.G2-HW-10002-2 Advance Information Design-In
Page 91 of 116
 Avoid coupling of any noisy signals to microphone input 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_P and MIC_N are sensed differentially within the module. Therefore they should be routed as a
differential pair up to the audio signal source
 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
 The bias for an external electret active microphone is not provided by the module. Verify that microphone is
properly biased from an external low noise supply and verify that the supply noise is properly filtered
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
 Consider enlarging PCB lines, to reduce series resistive losses, when the audio output is directly connected to
low impedance speaker transducer
 Use twisted pair cables for balanced audio usage
 If DC decoupling is required, a large capacitor needs to be used, typically in the microFarad range,
depending on the load impedance, in order to not increase the lower cut-off frequency of its High-Pass RC
filter response
2.2.1.5 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 pins have one or more dedicated via down to the application board solid ground layer
 The shielding metal tabs are connected to GND, and are a fundamental part of electrical grounding and
thermal heat-sink. Connect them to board solid ground layer, by soldering them on the baseboard using
PCB plated through holes connected to GND net
 If the application board is a multilayer PCB, then it is required to connect 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
2.2.1.6 Other sensitive pins
A few other pins on the LISA-U1/LISA-H1 series modules requires careful layout.
 RTC supply (V_BCKP): avoid injecting noise on this voltage domain as it may affect the stability of sleep
oscillator