ATA3742_07 ATMEL [ATMEL Corporation], ATA3742_07 Datasheet - Page 5

• Manufacturer Part Number: ATA3742_07
• Description: UHF ASK/FSK Receiver
• Manufacturer: ATMEL [ATMEL Corporation]

4900B–RKE–11/07
To determine f
frequency is f
is tuned by the crystal frequency f
f
The relation is designed to achieve the nominal IF frequency of f
tions. For applications where f
f
f
ferent conditions.
The RF input either from an antenna or from a generator must be transformed to the RF input
pin LNA_IN. The input impedance of that pin is provided in the electrical parameters. The para-
sitic board inductances and capacitances also influence the input matching. The RF receiver
ATA3742 exhibits its highest sensitivity at the best signal-to-noise ratio in the LNA. Hence, noise
matching is the best choice for designing the transformation network.
A good practice when designing the network is to start with power matching. From that starting
point, the values of the components can be varied to some extent to achieve the best sensitivity.
If a SAW is implemented into the input network, a mirror frequency suppression of P
can be achieved. There are SAWs available that exhibit a notch at f = 2 MHz. These SAWs
work best for an intermediate frequency of IF = 1 MHz. The selectivity of the receiver is also
improved by using a SAW. In typical automotive applications, a SAW is used.
Figure 3-2 on page 6
f
SAW. The input matching networks shown in
for the parameters given in the
Table 3-1.
MODE
MODE
Conditions
f
f
300 MHz < f
365 MHz < f
LO
RF
IF
RF
RF
RF
is then dependent on the logical level at pin MODE and on f
that depends on the logic level at pin MODE. This is described by the following formulas:
= 433.92 MHz, MODE must be set to “1”. For other RF frequencies, f
= 433.92 MHz using a SAW.
= 315 MHz, MODE = 0
= 433.92 MHz, MODE = 1
=
=
0 (USA) f
1 (Europe) f
RF
RF
IF
< 365 MHz, MODE = 0
< 450 MHz, MODE = 1
LO
Calculation of LO and IF Frequency
= 1 MHz. To achieve a good accuracy of the filter's corner frequencies, the filter
, the construction of the IF filter must be considered at this point. The nominal IF
IF
=
IF
--------- -
314
=
f
LO
shows a typical input matching network for f
----------------- -
432.92
f
LO
“Electrical Characteristics” on page
Figure 3-3 on page 6
RF
XTO
= 315 MHz, MODE must be set to “0”. In the case of
. This means that there is a fixed relation between f
Local Oscillator Frequency
f
f
f
f
LO
LO
LO
LO
= 314 MHz
= 432.92 MHz
=
=
Figure 3-3 on page 6
------------------- -
1
--------------------------- -
1
+
+
f
RF
--------- -
314
----------------- -
432.92
f
RF
1
1
illustrates input matching to 50 without a
RF
.
Table 3-1
IF
26.
are the reference networks
= 1 MHz for most applica-
Intermediate Frequency
f
f
f
f
IF
IF
IF
IF
= 1 MHz
= 1 MHz
IF
=
=
is not equal to 1 MHz.
--------- -
314
----------------- -
432.92
f
RF
LO
summarizes the dif-
f
LO
= 315 MHz and
ATA3742
Ref
= 40 dB
IF
and
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