TDA5150 Datasheet, PDF (42/106 Pages) Infineon Technologies AG – On-chip, high resolution fractional-N synthesizer and Sigma-Delta modulator with ASK, FSK, GFSK options

TDA 5150
TDA 5150 Functional Description
The Gaussian shaping is defined as a number of fixed frequency steps (transitions)
between the 2 FSK frequencies, corresponding to Low and High, or 0 and 1 on the
modulator input. It is understood that the steps are counted over one edge of the data
chip. Ideally these 16 steps are distributed over the complete data chip length, which
means there are 16 gaussian filter steps per chip or N_GF = 16. Selecting N_GF > 16 will
reduce the shaping effect and selecting N_GF < 16 will cause a reduction of signal
information, with minimal positive effect on the obtained RF spectrum.
.
1
0
Data chip
1
0
1
0
16 steps/chip
= ideal gaussian
25 steps/chip
11 steps/chip
Figure 15 Influence of the Gaussian Divider on Data Shaping
The content of GFDIV is calculated as follows:
GFDIV
=
-------------^f--^X---^O----^S---^C--------------
chiprate × N_GF
–
1
It is recommended to program the GFDIV register in such way, that the GF divider NGF
is 16 times the chip-rate. This allows optimum Gaussian filtering.
Data Sheet
42
V 1.0, July 2009