TDA5240 Datasheet, PDF (35/284 Pages) Infineon Technologies AG – Enhanced Sensitivity Multi-Channel Quad-Configuration Receiver

TDA5240
Functional Description
2.4.7 RSSI Peak Detector
The IC possesses several digital RSSI peak level detectors. The RSSI level is averaged
over 4 samples before it is fed to any of the peak detectors. This prevents the evaluated
peak values to be dominated by single noise peaks.
fsys
ADC Sampling
Clock Generation
fA D C
A
from
D
RSSI
Generator
RSSI Slope
RSSI Offset
Divide
by 4
fA D C/4
Integrate
Dump
RSSI
I&D Averaging Filter
to
ASK path
Figure 13 Peak Detector Unit
Compare
Peak Detector
Payload
Update
Peak
Value
Load
Update
Peak Value
Register
Peak
Detector
Track
Control
EOM
RSSIPPL
FSYNC
Bit
position
Compare
Peak Detector
Update
Peak-
Value
Load
&
RSSIPRX
RX_RUN
Read Access to
Register RSSIPRX
from
FSM
from
SPI Controller
RSSIRX
Peak Detector Payload is used to measure the input signal power of a received and
accepted data telegram. It is read via SFR RSSIPPL.
Observation of the RSSI signal starts at the detection of a TSI (FSYNC) and ends with
the detection of EOM. The internal RSSIPPL value is cleared after FSYNC. The
evaluated RSSI peak level RSSIPPL is transferred to the RSSIPPL register at EOM.
Starting the observation of the RSSI level can be delayed by a selectable number of data
bits and is controlled by the register x_PKBITPOS. A latency in the generation of FSYNC
and EOM of approx. 2..3 bits in relation to the contents of the Peak Detector must be
considered. Within the boundaries described, the register RSSIPPL always contains the
peak value of the last completely received data telegram. The register RSSIPPL is reset
to 0 at power up reset only.
Peak Detector is used to measure RSSI independent of a data transfer and to digitally
trim RSSI. It is read via SFR RSSIPRX.
Observation of the RSSI signal is active whenever the RX_RUN signal is high. The
RSSIPRX register is refreshed and the Peak Detector is reset after every read access to
RSSIPRX.
It may be required to read RSSIPRX twice to obtain the required result. This is because,
for example, during a trim procedure in which the input signal power is reduced, after
Data Sheet
35
V4.0, 2010-02-19