ATA5745-EK Atmel, ATA5745-EK Datasheet - Page 18

• Manufacturer Part Number: ATA5745-EK
• Description: BOARD RCVR 433MHZ RKE/TPMS
• Manufacturer: Atmel
• Type: Receiver, ASK/FSKr

Specifications of ATA5745-EK

• Frequency: 433MHz ~ 435MHz
• For Use With/related Products: ATA5745
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

4. Sensitivity Reduction
The output voltage of the RSSI amplifier is internally compared to a threshold voltage V
.
Th_red
V
is determined by the value of the external resistor R
. R
is connected between
Th_red
Sense
Sense
the pins SENSE and VS3V_AVCC (see
Figure 10-1 on page
28). The output of the comparator
is fed into the digital control logic. By this means, it is possible to operate the receiver at a lower
sensitivity.
If the level on input pin SENSE_CTRL is low, the receiver operates at full sensitivity.
If the level on input pin SENSE_CTRL is high, the receiver operates at a lower sensitivity. The
reduced sensitivity is defined by the value of R
, the maximum sensitivity by the sig-
Sense
nal-to-noise ratio of the LNA input. The reduced sensitivity depends on the signal strength at the
output of the RSSI amplifier.
Since different RF input networks may exhibit slightly different values for the LNA gain, the sen-
sitivity values given in the electrical characteristics refer to a specific input matching. This
matching is illustrated in
Figure 2-1 on page 6
and exhibits the best possible sensitivity.
If the sensitivity reduction feature is not used, pin SENSE can be left open, pin SENSE_CTRL
must be set to GND.
To operate with reduced sensitivity, pin SENSE_CTRL must be set to high before the RX signal
path will be enabled by setting pin RX to high (see
Figure 4-1 on page
19). As long as the RSSI
level is lower than V
(defined by the external resistor R
) no data stream is available on
Th_red
Sense
pin DATA_OUT (low level on pin DATA_OUT). An internal RS flip-flop will be set to high the first
time the RSSI voltage crosses V
, and from then on the data stream will be available on pin
Th_red
DATA_OUT. From then on the receiver also works with full sensitivity. This makes sure that a
telegram will not be interrupted if the RSSI level varies during the transmission. The RS flip-flop
can be set back, and thus the receiver switched back to reduced sensitivity, by generating a pos-
itive pulse on pin ASK_NFSK (see
Figure 4-2 on page
19). In FSK mode, operating with reduced
sensitivity follows the same way.
ATA5745/ATA5746 [Preliminary]
18
4596B–RKE–06/07