T5743P3 ATMEL [ATMEL Corporation], T5743P3 Datasheet - Page 7

• Manufacturer Part Number: T5743P3
• Description: UHF ASK/FSK Receiver
• Manufacturer: ATMEL [ATMEL Corporation]

Analog Signal Processing
IF Amplifier
RSSI Amplifier
4569A–RKE–12/02
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
the center frequency.
The T5743 is available with two different IF bandwidths. T5743P3, the version with
B
used. The receiver T5743P6 employs an IF bandwidth of B
can be used together with the U2741B in ASK and FSK mode. If used in ASK applica-
tions, it allows higher tolerances for the receiver and PLL transmitter crystals. SAW
transmitters exhibit much higher transmit freqeuncy tolerances compared to PLL trans-
mitters. Generally, it is necessary to use B
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 DR
RSSI amplifier is 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.
The output voltage of the RSSI amplifier is internally compared to a threshold voltage
V
nected between Pin SENS and GND or V
digital control logic. By this means it is possible to operate the receiver at a lower
sensitivity.
If R
If R
sitivity is defined by the value of R
ratio of the LNA input. The reduced sensitivity depends on the signal strength at the out-
put of the RSSI amplifier.
Since different RF input networks may exhibit slightly different values for the LNA gain,
the sensitivity values given in the electrical characteristics refer to a specific input
matching. This matching is illustrated in Figure 6 and exhibits the best possible
sensitivity.
R
switched from 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 Figure 7 is issued at Pin DATA to indicate that the
receiver is still active (see also figure 34).
Figure 7. Steady L State Limited DATA Output Pattern
RF
IF
Th_red
Sens
= 433.92 MHz is used. For other RF input frequencies refer to Table 1 to determine
Sens
= 300 kHz, is well suited for ASK systems where Atmel’s PLL transmitter U2741B is
Sens
can be connected to V
. V
is connected to V
is connected to GND, the receiver operates at full sensitivity.
Th_red
is determined by the value of the external resistor R
DATA
S
, the receiver operates at a lower sensitivity. The reduced sen-
t
DATA_min
S
or GND via a microcontroller. The receiver can be
IF
Sens
= 1 MHz for applications where f
, the maximum sensitivity by the signal-to-noise
t DATA_L_max
S
IF
. The output of the comparator is fed into the
= 600 kHz together with such transmitters.
IF
= 600 kHz. Both versions
RSSI
Sens
RF
= 60 dB. If the
. R
= 315 MHz or
T5743
Sens
is con-
7