Specifications

LEON-G100/G200 - System Integration Manual
GSM.G1-HW-09002-C Preliminary Design-In
Page 55 of 75
The large current generates a magnetic field that is not well isolated by PCB ground layers and which may
interact with other analog modules (e.g. VCO) even if placed on opposite side of PCB. In this case route VCC
away from other sensitive functional units
The typical GSM burst has a periodic nature of approx. 217 Hz, which lies in the audible audio range. Avoid
coupling between VCC and audio lines (especially microphone inputs)
If VCC is protected by transient voltage suppressor / reverse polarity protection diode to ensure that the
voltage maximum ratings are not exceeded, place the protecting device along the path from the DC source
toward LEON-G100/G200, preferably closer to the DC source (otherwise functionality may be compromised)
VCC pad is longer than other pads, and requires a “No-Routing” area for any other signals on the top layer
of the application board PCB, below the LEON-G100/G200
VCC line should be wide and short
Route away from sensitive analog signals
2.2.1.3 Analog Audio
Accurate analog audio design is very important to obtain clear and high quality audio. The GSM signal burst has
a repetition rate of 271 Hz that lies in the audible range. A careful layout is required to reduce the risk of noise
pickup from audio lines due to both VCC burst noise coupling and RF detection.
Analog audio is separated in the two paths,
1. Audio Input (Uplink path): MIC_BIASx, MIC_GNDx
2. Audio Outputs (Downlink path): SPK_P / SPK_N, HS_P
The most sensitive is the Uplink path, since the analog input signals are in the µV range. The two microphone
inputs have the same electrical characteristics, and it is recommended to implement their layout with the same
routing rules.
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. Note that
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 kΩ 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.