Specifications

LEON-G100/G200 - System Integration Manual
GSM.G1-HW-09002-C Preliminary Design-In
Page 54 of 75
The transmission line must be routed in a section of the PCB where minimal interference from noise sources
can be expected
Route ANT line far from other sensitive circuits as it is a source of electromagnetic interference
Avoid coupling with VCC routing and analog Audio lines
Ensure solid metal connection of the adjacent metal layer on the PCB stack-up to main ground layer
Add GND vias around transmission line
Ensure no other signals are routed parallel to transmission line, or that other signals cross on adjacent metal
layer
If the distance between the transmission line and the adjacent GND area (on the same layer) does not
exceed 5 times the track width of the micro strip, use the “Coplanar Waveguide” model for 50 Ω
characteristic impedance calculation
Don’t route microstrip line below discrete component or other mechanics placed on top layer
When terminating transmission line on antenna connector (or antenna pad) it is very important to strictly
follow the connector manufacturer’s recommended layout
GND layer under RF connectors and close to buried vias should be cut out in order to remove stray
capacitance and thus keep the RF line 50 Ω. In most cases the large active pad of the integrated antenna or
antenna connector needs to have a GND keep-out at least on first inner layer to reduce parasitic capacitance
to ground. Note that the layout recommendation is not always available from connector manufacturer: e.g.
the classical SMA Pin-Through-Hole needs to have GND cleared on all the layers around the central pin up to
annular pads of the four GND posts. Check 50 Ω impedance of ANT line
Ensure no coupling occurs with other noisy or sensitive signals
2.2.1.2 Main DC supply connection
The DC supply of LEON-G100/G200 modules is very important for the overall performance and functionality of
the integrated product. For detailed description check the design guidelines in section 1.5.2. Some main
characteristics are:
VCC connection may carry a maximum burst current in the order of 2.5 A. Therefore, it is typically
implemented as a wide PCB line with short routing from DC supply (DC-DC regulator, battery pack, etc)
The module automatically initiates an emergency shutdown if supply voltage drops below hardware
threshold. In addition, reduced supply voltage can set a worst case operation point for RF circuitry that may
behave incorrectly. It follows that each voltage drop in the DC supply track will restrict the operating margin
at the main DC source output. Therefore, the PCB connection has to exhibit a minimum or zero voltage
drop. Avoid any series component with Equivalent Series Resistance (ESR) greater than a few mΩs
Given the large burst current, VCC line is a source of disturbance for other signals. Therefore route VCC
through a PCB area separated from sensitive analog signals. Typically it is good practice to interpose at least
one layer of PCB ground between VCC track and other signal routing
The VCC supply current supply flows back to main DC source through GND as ground current: provide
adequate return path with suitable uninterrupted ground plane to main DC source;
A tank capacitor with low ESR is often used to smooth current spikes. This is most effective when placed as
close as possible to VCC. From main DC source, first connect the capacitor and then VCC. If the main DC
source is a switching DC-DC converter, place the large capacitor close to the DC-DC output and minimize
the VCC track length. Otherwise consider using separate capacitors for DC-DC converter and LEON-
G100/G200 tank capacitor. Note that the capacitor voltage rating may be adequate to withstand the
charger over-voltage if battery-pack is used
VCC is directly connected to the RF power amplifier. Add capacitor in the pF range from VCC to GND along
the supply path
Since VCC is directly connected to RF Power Amplifier, voltage ripple at high frequency may result in
unwanted spurious modulation of transmitter RF signal. This is especially seen with switching DC-DC
converters, in which case it is better to select the highest operating frequency for the switcher and add a
large L-C filter before connecting to LEON-G100/G200 in the worst case