Hi folks,
we just completed a custom RF interface board for our product.
It's a simple SPI-to-Antenna board with TCXO and BALF, in the 862-868 MHz band.
The TCXO is powered by an LDO at 1.8 Volt. This allows us to use a battery.
The S2-LP is powered externally at 3.3 Volt (internally it uses its DC/DC at 1.8 Volt)
The RF performances are great:
The CW signal has a variance of just 300 Hz aournd the carrier at 868 MHz
TX: we got 4 dBm better than the same board with a quartz crystal
RX: we got 2 dBm better than the same board with a quartz crystal
TCXO
1.8 V 50 MHz+/- 0.5 ppm -40, +85 Celsius)
Manufacturer: KDS
PN: DSB211SDN
It can be purchased in Italy from CODICO.
BALUN:
MANUFACURER: ST
PN: BALF-SPI2-01D3
PCB:
MANUFACTURER: MD srl Italy
LAMINATE: FR4 common
LAYERS: 4
L1 = RF signals
L2 = GND
L3 = Just 3 traces of VDD (*)
L4 = SPI signals
(*) No power plane at all. The layer is empty except for 3 traces of VDD
To achieve this result we followed all the ST guidelines.
In particular, the BALUN needs to be routed according to ST guidelines.
No VDD traces must be routed below the S2-LP chip or the BALF.
Enrico Migliore
