xe1205 Semtech Corporation, xe1205 Datasheet - Page 38

• Manufacturer Part Number: xe1205
• Description: Low-power, High Link Budget Integrated Uhf Transceiver
• Manufacturer: Semtech Corporation

Figure 23 illustrates the switching time between two carrier frequencies in receive mode. TS_RFSW is defined as the
switching time of the frequency synthesizer and the time needed by the base band filter to reach the steady-state when
the boost process is used (Init_filter set to 11 ).
Figure 24 shows the switching time between two carrier frequencies in transmit mode. TS_TFSW is defined as the
switching time of the frequency synthesizer and the time required by the power amplifier to reach the steady-state
operating conditions.
7.3.2
If MCParam_Select_mode is high then the transceiver mode is fixed by SW(1:0) pins and register
MCParam_Chip_mode can be used in read mode but has no effect on the transceiver mode.
The reference clock used for the frequency synthesizer and the internal digital circuitry may be generated by either an
external 39 MHz quartz crystal or a TCXO or an external clock. If an external clock is used, the register OSCParam_Osc
has to be set high, and the 39 MHz clock signal should to be supplied to the pin XTA and the pin XTB should be left
open. If a TCXO is used, its output signal should be connected to the pin XTA and the pin XTB should be left.
The transceiver can be used with a 39 MHz fundamental mode quartz crystal or with a 3
overtone operation requires an internal resistor to be connected in parallel with the crystal. This resistor can be
connected by programming the register OSCParam_Resxosc(3:0). The required value depends on the crystal
© Semtech 2007
7.4
Programmed frequency
NSS_CONFIG
Actual frequency
Programmed frequency
NSS_CONFIG
Actual frequency
Actual mode
Actual mode
XE1205 switching time using SW(1:0) pins.
SELECTION OF THE REFERENCE FREQUENCY
Figure 24. Switching between two carrier frequencies in transmit mode.
Figure 23. Switching between two carrier frequencies in receive mode.
f1
f1
f1
f1
transmit
receive
38
TS_RFSW
TS_TFSW
f2
f2
f2
f2
rd
overtone crystal. Third
XE1205
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