TDA5225 Datasheet, PDF (26/176 Pages) Infineon Technologies AG – Enhanced Sensitivity Multi-Channel Quad-Configuration Receiver

TDA5225
2.4.6 ASK and FSK Demodulator
Functional Description
AFC track/freeze
AFC RF PLL ctrl
loop filter
B = 50..300kHz
channel filter FM limiter
PPF2
BP
2nd
conversion
RSSI
FSK
Temp
VDDD/2
image suppression /
band limitation (noise)
33 / 46 / 65 / 93 / 132 /
190 / 239 / 282 kHz
(2sided PDF BW)
buffer
Mux ADC
ASK
Div
RSSI Slope Dig. Gain
RSSI Offset Control
Peak Memory
Filter
delog
AGC
FSK/ASK
Rate adapter
Bypass
Rate doubler
Decimation
Demodulated
Data
8 … 16 samples /chip
(data rate dependent )
Analog Gain Control
RSSI
fSystem
RSSI Peak
Detector
register
RSSIPMF
register
RSSIPWU
(internal
signal)
RSSIPWU
register
End of config/
>
channel
WU event
Begin of config /
channel ,
x*WULOT
TH, BL, BH
Figure 10 Functional Block Diagram ASK/FSK Demodulator
The IC comprises two separate demodulators for ASK and FSK.
After combining FSK and ASK data path, a sampling rate adaptation follows to meet an
output oversampling between 8 and 16 samples per chip. Finally, an oversampling of 8
samples per chip can be achieved using a fractional sample rate converter (SRC) with
linear interpolation (for further details see Figure 15).
2.4.6.1 ASK Demodulator
The RSSI generator delivers a DC signal proportional to the applied input power at a
logarithmic scale (dBm) and is also used as an ASK demodulator. Via a programmable
anti-aliasing filter this signal is converted to the digital domain by means of a 10-bit ADC.
For the AM demodulation a signal proportional to the linear power is required. Therefore
a conversion from logarithmic scale to linear scale is necessary. This is done in the digital
domain by a nonlinear filter together with an exponential function. The analog RSSI
signal after the anti-aliasing filter is available at the RSSI pin via a buffer amplifier. To
enable this buffer the SFR control bit RSSIMONEN must be set. The anti-aliasing filter
can be by-passed for visualization on the RSSI pin (see AAFBYP control bit).
Data Sheet
26
V1.0, 2010-02-19