ATA5760 ATMEL Corporation, ATA5760 Datasheet - Page 6

• Manufacturer Part Number: ATA5760
• Description: Ata5760 Uhf Ask/fsk Receiver
• Manufacturer: ATMEL Corporation

4. Analog Signal Processing
4.1
4.2
6
IF Filter
Limiting RSSI Amplifier
ATA5760/ATA5761
The signals coming from the RF front-end are filtered by the fully integrated 4th-order IF filter.
The IF center frequency is
f
f
f
The nominal bandwidth is B
ATA5760N3.
The subsequent RSSI amplifier enhances the output signal of the IF amplifier before it is fed into
the demodulator. The dynamic range of this amplifier is R
operated within its linear range, the best S/N ratio is maintained in ASK mode. If the dynamic
range is exceeded by the transmitter signal, the S/N ratio is defined by the ratio of the maximum
RSSI output voltage and the RSSI output voltage due to a disturber. The dynamic range of the
RSSI amplifier is exceeded if the RF input signal is about 60 dB higher compared to the RF input
signal at full sensitivity.
In FSK mode the S/N ratio is not affected by the dynamic range of the RSSI amplifier, because
only the hard limited signal from a high gain limiting amplifier is used by the demodulator.
The output voltage of the RSSI amplifier is internally compared to a threshold voltage V
V
SENS and GND or V
means it is possible to operate the receiver at a lower sensitivity.
If R
nect the pin SENS directly to GND to get the maximum sensitivity.
If R
defined by the value of R
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
the same time power matching at RF_IN.
R
full sensitivity to reduced sensitivity or vice versa at any time. In polling mode, the receiver will
not wake up if the RF input signal does not exceed the selected sensitivity. If the receiver is
already active, the data stream at pin DATA will disappear when the input signal is lower than
defined by the reduced sensitivity. Instead of the data stream, the pattern according to
4-1
IF
IF
IF
Th_red
Sens
= 950 kHz for the 868.3 MHz and B
= 989 kHz for the 868.3 MHz and B
= 1 MHz for the 915 MHz version.
Sens
Sens
is issued at pin DATA to indicate that the receiver is still active (see
can be connected to V
is determined by the value of the external resistor R
is connected to V
is connected to GND, the receiver switches to full sensitivity. It is also possible to con-
S
. The output of the comparator is fed into the digital control logic. By this
Figure 14-1 on page 30
S
, the receiver operates at a lower sensitivity. The reduced sensitivity is
Sens
S
, the maximum sensitivity by the signal-to-noise ratio of the LNA
or GND via a microcontroller. The receiver can be switched from
IF
= 600 kHz for ATA5760/ATA5761 and B
IF
IF
= 600 kHz version,
= 300 kHz version and
and exhibits the best possible sensitivity and at
Sens
RSSI
. R
= 60 dB. If the RSSI amplifier is
Sens
is connected between pin
Figure 13-2 on page
IF
= 300 kHz for
4896C–RKE–04/06
Figure
Th_red
28).
.