WE2408 View Datasheet(PDF) - Unspecified
Part Name
Description
MFG CO.
'WE2408' PDF : 36 Pages View PDF
WiNEDGE & WiRELESS
Winceiver WE2408
2.4GHz Single Chip FM Transceiver
FM MODULATION
FM DEVIATION
The transmitter utilizes direct modulation method where the modulation signal is directly applied to the
PLL loop filter.
FM deviation is depending on the a.c. voltage level of the applied modulation signal as well as TVCO
gain. TVCO gain is in term, dependent on the TVCO frequency and TPLL voltage. It is normally
desirable for FM deviation to be consistent for a given modulating voltage level.
For a circuit that is designed to operate at a Tx frequency band, the TVCO frequency is fixed by
Transmit Frequency Register.
However, the locked TPLL voltage may differ from one unit to another. This is mainly due to the
tolerance of external TVCO inductors and the choice of Tx trim bit which set the internal capacitance.
The solution is either to use tight tolerance TVCO inductors or a potential divider to adjust the voltage
level of the modulating signal.
Using tight tolerance inductors, such as PCB printed inductors, FM deviation varies between board to
board can be maintained within +/-20%. For more accurate FM deviation, a pot meter is required to
adjust the modulating signal level.
FM MODULATOR
If there is a change in PLL loop filter, the Tx modulator components have to be changed to get the
desired frequency response and Tx FM deviation.
Values for modulator components can be determined by simulation. How VCO frequency responses
to an input to the modulator circuit (ac or transient) are simulated to obtain the correct modulator RC
combination. Below is the circuit for modulator simulation.
© 2003 WiNEDGE & WiRELESS PTE LTD
Rev Date: 2003 May 23
Page 20
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