ata5724p3c-tkqy ATMEL Corporation, ata5724p3c-tkqy Datasheet - Page 6

• Manufacturer Part Number: ata5724p3c-tkqy
• Description: Uhf Ask/fsk Receiver
• Manufacturer: ATMEL Corporation

4. Analog Signal Processing
4.1
4.2
6
IF Filter
Limiting RSSI Amplifier
Atmel ATA5723C/ATA5724C/ATA5728C
To determine f
quency is f
tuned by the crystal frequency f
and f
f
f
f
The relationship is designed to achieve the nominal IF frequency of:
f
f
f
The RF input either from an antenna or from an RF generator must be transformed to the RF
input pin LNA_IN. The input impedance of this pin is provided in the electrical parameters. The
parasitic board inductances and capacitances influence the input matching. The RF receiver
Atmel ATA5723C/ATA5724C/ATA5728C exhibits its highest sensitivity if the LNA is power
matched. Because of this, matching to a SAW filter, a 50 or an antenna is easier.
Figure 14-1 on page 32
f
in
characteristics.
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 300kHz for Atmel ATA5723C and Atmel ATA5724C and 600kHz for
Atmel ATA5728C.
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
fier 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 approximately 60dB higher
compared to the RF input signal at full sensitivity.
The S/N ratio is not affected by the dynamic range of the RSSI amplifier in FSK mode because
only the hard limited signal from a high-gain limiting amplifier is used by the demodulator.
IF
IF
IF
IF
IF
IF
RF
IF
IF
IF
Table 14-2 on page 32
= f
= f
= f
= 987kHz for the 315MHz and B
= 987kHz for the 433.92MHz and B
= 947.8kHz for the 868.3MHz and B
= 987kHz for the 315MHz and B
= 987kHz for the 433.92MHz and B
= 947.9kHz for the 868.3MHz and B
= 315MHz, f
LO
LO
LO
LO
.
/318 for the 315MHz band (Atmel
/438 for the 433.92MHz band (Atmel ATA5724C)
/915 for the 868.3MHz band (Atmel ATA5728C)
IF
= 950kHz. To achieve a good accuracy of the filter corner frequencies, the filter is
LO
RF
, the construction of the IF filter must be considered. The nominal IF fre-
= 433.92MHz or f
“Application Circuit” shows a typical input matching network for
is the reference network for the parameters given in the electrical
XTO
IF
IF
. This means that there is a fixed relationship between f
RF
= 300kHz (Atmel ATA5723C)
= 300kHz (Atmel ATA5723C)
IF
IF
= 868.3MHz to 50 . The input matching network shown
IF
IF
= 300kHz (Atmel ATA5724C)
= 300kHz (Atmel ATA5724C)
®
= 600kHz (Atmel ATA5728C)
= 600kHz (Atmel ATA5728C)
ATA5723C)
RSSI
= 60dB. If the RSSI ampli-
9248A–RKE–09/11
IF