T5743P3 ATMEL [ATMEL Corporation], T5743P3 Datasheet - Page 5

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

4569A–RKE–12/02
This is described by the following formulas:
The relation is designed to achieve the nominal IF frequency of f
applications. For applications where f
case of f
not equal to 1 MHz. f
Table 1 summarizes the different 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 parame-
ters. The parasitic board inductances and capacitances also influence the input
matching. The RF receiver T5743 exhibits its highest sensitivity at the best signal-to-
noise ratio in the LNA. Hence, noise matching is the best choice for designing the trans-
formation 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
DP
Df = 2 MHz. These SAWs work best for an intermediate frequency of f
selectivity of the receiver is also improved by using a SAW. In typical automotive appli-
cations, a SAW is used.
Figure 5 shows a typical input matching network, for f
433.92 MHz using a SAW. Figure 6 illustrates an according input matching to 50 W
without a SAW. The input matching networks shown in Figure 6 are the reference net-
works for the parameters given in the electrical characteristics.
Table 1. Calculation of LO and IF Frequency
MODE
MODE
Conditions
f
f
300 MHz < f
MODE = 0
365 MHz < f
MODE = 1
RF
RF
Ref
= 315 MHz, MODE = 0
= 433.92 MHz, MODE = 1
= 40 dB can be achieved. There are SAWs available that exhibit a notch at
=
=
RF
0 (USA) : f
1 (Europe) : f
= 433.92 MHz, MODE must be set to ‘1’. For other RF frequencies, f
RF
RF
< 365 MHz,
< 450 MHz,
IF
IF
is then dependent on the logical level at Pin MODE and on f
IF
=
--------- -
314
=
f
LO
----------------- -
432.92
Local Oscillator Frequency
f
f
f
f
f
LO
LO
LO
LO
LO
= 314 MHz
= 432.92 MHz
=
=
-------------------
1
--------------------------- -
1
+
+
f
RF
RF
--------- -
314
f
----------------- -
432.92
RF
1
1
= 315 MHz, MODE must be set to ‘0’. In the
Intermediate Frequency
f
f
IF
IF
f
f
RF
IF
IF
= 1 MHz
= 1 MHz
=
=
= 315 MHz and f
--------- -
314
----------------- -
432.92
f
LO
IF
f
LO
= 1 MHz for most
IF
= 1 MHz. The
T5743
R F
IF
RF
is
=
5
.