U3741BM-M2FLG3 TEMIC [TEMIC Semiconductors], U3741BM-M2FLG3 Datasheet - Page 4

• Manufacturer Part Number: U3741BM-M2FLG3
• Description: UHF ASK/FSK Receiver
• Manufacturer: TEMIC [TEMIC Semiconductors]

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. If the
filter components are changed for any reason please
notify that the maximum capacitive load at Pin LF is
limited. If the capacitive load is exceeded, a bitcheck may
no longer be possible since f
before the bitcheck starts to evaluate the incoming data
stream. Self polling does therefore also not work in that
case.
f
IF frequency f
To determine f
considered at this point. The nominal IF frequency is
f
corner frequencies, the filter is tuned by the crystal
frequency f
between f
logic level at pin mode. This is described by the following
formulas:
Table 1. Calculation of LO and IF frequency
U3741BM
f
f
300 MHz < f
365 MHz < f
4 (25)
LO
IF
RF
RF
= 1 MHz. To achieve a good accuracy of the filter’s
is determined by the RF input frequency f
= 315 MHz, MODE = 0
= 433.92 MHz, MODE = 1
f
LO
IF
LFGND
LFVCC
= f
DVCC
XTO
XTO
and f
LF
RF
RF
RF
IF
LO
. This means that there is a fixed relation
Figure 4. PLL peripherals
using the following formula:
< 365 MHz, MODE = 0
< 450 MHz, MODE = 1
– f
, the construction of the IF filter must be
Conditions
LO
IF
V
V
. This relation is dependent on the
S
S
C9
R1
LO
C10
cannot settle in time
C
Preliminary Information
L
R1 = 820
C9 = 4.7 nF
C10 = 1 nF
RF
f
f
f
f
LO
LO
LO
LO
and the
Local Oscillator Frequency
= 314 MHz
= 432.92 MHz
+
+
W
1
1
)
)
f
RF
f
RF
314
432.92
1
The relation is designed to achieve the nominal IF
frequency of f
applications where f
‘0’. In the case of f
to ‘1’. For other RF frequencies, f
f
on f
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 parasitic board inductances and
capacitances also influence the input matching. The RF
receiver U3741BM 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
There are SAWs available that exhibit a notch at
D
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 5 shows a typical input matching network, for
f
Figure 6 illustrates an according input matching to 50
without a SAW. The input matching networks shown in
figure 6 are the reference networks for the parameters
given in the electrical characteristics.
1
IF
RF
MODE
MODE
f = 2 MHz. These SAWs work best for an intermediate
is then dependent on the logical level at Pin MODE and
RF
= 315 MHz and f
. Table 1 summarizes the different conditions.
+
+
0 (USA) f
1 (Europe) f
IF
= 1 MHz for most applications. For
RF
RF
= 433.92 MHz, MODE must be set
f
f
RF
f
f
IF
IF
= 315 MHz, MODE must be set to
LO
LO
IF
= 1 MHz
= 1 MHz
D
= 433.92 MHz using a SAW.
+
+
+
IF
Intermediate Frequency
P
Ref
+
314
432.92
f
314
f
RF
LO
f
= 40 dB can be achieved.
432.92
RF
IF
f
LO
is not equal to 1 MHz.
Rev. A1, 15-Oct-98
W