T5744 ATMEL [ATMEL Corporation], T5744 Datasheet - Page 4

• Manufacturer Part Number: T5744
• Description: UHF ASK Receiver
• Manufacturer: ATMEL [ATMEL Corporation]

4
T5744
Figure 4. PLL Peripherals
The passive loop filter connected to Pin LF is designed for a loop bandwidth of BLoop =
100 kHz. This value for BLoop exhibits the best possible noise performance of the LO.
Figure 4 shows the appropriate loop filter components to achieve the desired loop
bandwidth
f
ing formula:
To determine f
nominal IF frequency is f
quencies, the filter is tuned by the crystal frequency f
fixed relation between f
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 T5744 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
D P
D 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 appli-
cations, a SAW is used.
LO
Ref
is determined by the RF input frequency f
f
MODE = 0 USA f
MODE = 1 Europe f
= 40 dB can be achieved. There are SAWs available that exhibit a notch at
LO
RF
= f
= 433.92 MHz, MODE must be set to '1'. For other RF frequencies, f
RF
- f
LO
IF
, the construction of the IF filter must be considered at this point. The
IF
IF
is then dependent on the logical level at Pin MODE and on f
IF
IF
= f
IF
= 1 MHz. To achieve a good accuracy of the filter's corner fre-
and f
LFGND
LFVCC
LO
= f
DVCC
XTO
LF
/314
LO
LO
/432.92
that depends on the logic level at pin mode. This is
V
V
S
S
RF
= 315 MHz, MODE must be set to '0'. In the
C9
R1
RF
and the IF frequency f
C10
C
L
C9 = 4.7 nF
C10 = 1 nF
XTO
R1 = 820 W
. This means that there is a
IF
IF
= 1 MHz for most
using the follow-
4521B–RKE–01/03
IF
RF
is
.