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Электронный компонент: U3741BM-M3FLG3

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U3741BM
Preliminary Information
Rev. A1, 15-Oct-98
1 (25)
UHF ASK/FSK Receiver
Description
The U3741BM is a multi-chip PLL receiver device
supplied in an SO20 package. It has been specially
developed for the demands of RF low-cost data
transmission systems with low data rates from 1 kBaud to
10 kBaud (1 kBaud to 3.2 kBaud for FSK) in Manchester
or Bi-phase code. The receiver is well suited to operate
with the TEMIC PLL RF transmitter U2741B. Its main
applications are in the areas of telemetering, security
technology and keyless-entry systems. It can be used in
the frequency receiving range of f
0
= 300 MHz to
450 MHz for ASK or FSK data transmission. All the
statements made below refer to 433.92-MHz and
315-MHz applications.
Features
D Minimal external circuitry requirements, no RF
components on the PC board except adaptation to the
receiver antenna
D High sensitivity, especially at low data rates
D Sensitivity reduction possible even while receiving
D Fully integrated VCO
D Low power consumption due to configurable self
polling with a programmable timeframe check
D Supply voltage 4.5 V to 5.5 V,
operating temperature range 40
C to 105
C
D Single-ended RF input for easy adaptation to
l/4 antenna or printed antenna on PCB
D Low-cost solution due to high integration level
D ESD protection according to MIL-STD. 883
(4KV HBM) except Pin POUT (2KV HBM)
D High image frequency suppression due to 1 MHz IF
in conjunction with a SAW front-end filter. Up to
40 dB is thereby achievable with newer SAWs.
D Programmable output port for sensitivity selection or
for controlling external periphery
D Communication to mC possible via a single,
bi-directional data line
D Power management (polling) is also possible by
means of a separate pin via the
mC
D 2 different IF bandwidth versions are available
(300 kHz and 600 kHz)
System Block Diagram
Demod.
IF Amp
LNA
VCO
PLL
XTO
Control
U3741BM
1...3
14917
mC
Power
amp.
XTO
VCO
PLL
U2741B
Antenna Antenna
UHF ASK/FSK
Remote control transmitter
UHF ASK/FSK
Remote control receiver
Encoder
M44Cx9x
1 Li cell
Keys
Figure 1. System block diagram
U3741BM
Rev. A1, 15-Oct-98
Preliminary Information
2 (25)
Ordering Information
Extended Type Number
Package
Remarks
U3741BM-M2FL
SO20
2: IF bandwidth of 300 kHz, tube
U3741BM-M2FLG3
SO20
2: IF bandwidth of 300 kHz, taped and reeled
U3741BM-M3FL
SO20
3: IF bandwidth of 600 kHz, tube
U3741BM-M3FLG3
SO20
3: IF bandwidth of 600 kHz, taped and reeled
Pin Description
1
2
3
4
5
6
7
8
10
9
19
18
17
16
14
15
13
12
11
20
AVCC
AGND
14844
DGND
MIXVCC
LNAGND
LNA_IN
FSK/ASK
CDEM
POUT
MODE
XTO
LFGND
LF
ENABLE
TEST
n.c.
LFVCC
DATA
DVCC
SENS
Figure 2. Pinning SO20
Pin
Symbol
Function
1
SENS
Sensitivity-control resistor
2
FSK/ASK Selecting FSK/ASK
Low: FSK, High: ASK
3
CDEM
Lower cut-off frequency data filter
4
AVCC
Analog power supply
5
AGND
Analog ground
6
DGND
Digital ground
7
MIXVCC Power supply mixer
8
LNAGND High-frequency ground LNA and
mixer
9
LNA_IN
RF input
10
n.c.
Not connected
11
LFVCC
Power supply VCO
12
LF
Loop filter
13
LFGND
Ground VCO
14
XTO
Crystal oscillator
15
DVCC
Digital power supply
16
MODE
Selecting 433.92 MHz /315 MHz
Low: 4.90625 MHz (USA)
High: 6.76438 (Europe)
17
POUT
Programmable output port
18
TEST
Test pin, during operation at GND
19
ENABLE
Enables the polling mode
Low: polling mode off
(sleep mode)
H:
polling mode on
(active mode)
20
DATA
Data output / configuration input
U3741BM
Preliminary Information
Rev. A1, 15-Oct-98
3 (25)
Block Diagram
15011
FSK/ASK
Demodulator
and data filter
IF Amp
IF Amp
4. Order
LPF
3 MHz
LPF
3 MHz
DEMOD_OUT
Limiter out
RSSI
Sensitivity
reduction
Standby logic
Polling circuit
and
control logic
FE
CLK
VCO
XTO
64
f
50 k
W
V
S
FSK/ASK
CDEM
AVCC
SENS
AGND
DGND
MIXVCC
LNAGND
LNA_IN
DATA
ENABLE
TEST
POUT
MODE
LFGND
LFVCC
XTO
LF
DVCC
LNA
Figure 3. Block diagram
RF Front End
The RF front end of the receiver is a heterodyne
configuration that converts the input signal into a 1-MHz
IF signal. According to figure 3, the front end consists of
an LNA (low noise amplifier) LO (local oscillator), a
mixer and RF amplifier.
The LO generates the carrier frequency for the mixer via
a PLL synthesizer. The XTO (crystal oscillator) generates
the reference frequency f
XTO
. The VCO (voltage-
controlled oscillator) generates the drive voltage
frequency f
LO
for the mixer. f
LO
is dependent on the
voltage at Pin LF. f
LO
is divided by factor 64. The divided
frequency is compared to f
XTO
by the phase frequency
detector. The current output of the phase frequency
detector is connected to a passive loop filter and thereby
generates the control voltage V
LF
for the VCO. By means
of that configuration V
LF
is controlled in a way that
f
LO
/64 is equal to f
XTO
. If f
LO
is determined, f
XTO
can be
calculated using the following formula:
f
XTO
= f
LO
/64
The XTO is a one-pin oscillator that operates at the series
resonance of the quartz crystal. According to figure 4, the
crystal should be connected to GND via a capacitor CL.
The value of that capacitor is recommended by the crystal
supplier. The value of CL should be optimized for the
individual board layout to achieve the exact value of f
XTO
and hereby of f
LO
. When designing the system in terms
of receiving bandwidth, the accuracy of the crystal and
the XTO must be considered.
U3741BM
Rev. A1, 15-Oct-98
Preliminary Information
4 (25)
DVCC
XTO
LF
LFVCC
LFGND
V
C
C10
R1
C9
S
L
V
S
R1 = 820
W
C9 = 4.7 nF
C10 = 1 nF
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. 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
LO
cannot settle in time
before the bitcheck starts to evaluate the incoming data
stream. Self polling does therefore also not work in that
case.
f
LO
is determined by the RF input frequency f
RF
and the
IF frequency f
IF
using the following formula:
f
LO
= f
RF
f
IF
To determine f
LO
, the construction of the IF filter must be
considered at this point. The nominal IF frequency is
f
IF
= 1 MHz. To achieve a good accuracy of the filter's
corner frequencies, the filter is tuned by the crystal
frequency f
XTO
. This means that there is a fixed relation
between f
IF
and f
LO
. This relation is dependent on the
logic level at pin mode. This is described by the following
formulas:
MODE
+ 0 (USA) f
IF
+
f
LO
314
MODE
+ 1 (Europe) f
IF
+
f
LO
432.92
The relation is designed to achieve the nominal IF
frequency of f
IF
= 1 MHz for most applications. For
applications where f
RF
= 315 MHz, MODE must be set to
`0'. In the case of f
RF
= 433.92 MHz, MODE must be set
to `1'. For other RF frequencies, f
IF
is not equal to 1 MHz.
f
IF
is then dependent on the logical level at Pin MODE and
on f
RF
. 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
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
DP
Ref
= 40 dB can be achieved.
There are SAWs available that exhibit a notch at
Df = 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 5 shows a typical input matching network, for
f
RF
= 315 MHz and f
RF
= 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 networks for the parameters
given in the electrical characteristics.
Table 1. Calculation of LO and IF frequency
Conditions
Local Oscillator Frequency
Intermediate Frequency
f
RF
= 315 MHz, MODE = 0
f
LO
= 314 MHz
f
IF
= 1 MHz
f
RF
= 433.92 MHz, MODE = 1
f
LO
= 432.92 MHz
f
IF
= 1 MHz
300 MHz < f
RF
< 365 MHz, MODE = 0
f
LO
+
f
RF
1
)
1
314
f
LO
+
f
RF
314
365 MHz < f
RF
< 450 MHz, MODE = 1
f
LO
+
f
RF
1
)
1
432.92
f
LO
+
f
RF
432.92
U3741BM
Preliminary Information
Rev. A1, 15-Oct-98
5 (25)
IN
IN_GND
OUT
OUT_GND
CASE_GND
B3555
U3741BM
C3
22p
L
25n
C16
100p
C17
8.2p
L3
TOKO LL2012
F27NJ
27n
C2
8.2p
L2
TOKO LL2012
F33NJ
33n
1
2
3,4 7,8
5
6
8
9
RF
IN
f
RF
= 433.92 MHz
14105
LNAGND
LNA_N
IN
IN_GND
OUT
OUT_GND
CASE_GND
B3551
U3741BM
C3
47p
L
25n
C16
100p
C17
22p
L3
TOKO LL2012
F47NJ
47n
C2
10p
L2
TOKO LL2012
F82NJ
82n
1
2
3,4 7,8
5
6
8
9
RF
IN
f
RF
= 315 MHz
14106
LNAGND
LNA_N
Figure 5. Input matching network with SAW filter
U3741BM
15p
25n
100p
3.3p
TOKO LL2012
F22NJ
22n
8
9
RF
IN
f
RF
= 433.92 MHz
14107
LNAGND
LNA_N
U3741BM
33p
25n
100p
3.3p
TOKO LL2012
F39NJ
39n
8
9
RF
IN
f
RF
= 315 MHz
14108
LNAGND
LNA_N
Figure 6. Input matching network without SAW filter
Please notify that for all coupling conditions (see
figures 5 and 6), the bond wire inductivity of the LNA
ground is compensated. C3 forms a series resonance
circuit together with the bond wire. L = 25 nH is a feed
inductor to establish a DC path. Its value is not critical but
must be large enough not to detune the series resonance
circuit. For cost reduction this inductor can be easily
printed on the PCB. This configuration improves the
sensitivity of the receiver by about 1 dB to 2 dB.
Analog Signal Processing
IF Amplifier
The signals coming from the RF front end are filtered by
the fully integrated 4th-order IF filter. The IF center
frequency is f
IF
= 1 MHz for applications where
f
RF
= 315 MHz or f
RF
= 433.92 MHz is used. For other
RF input frequencies refer to table 1 to determine the
center frequency.
The U3741BM is available with 2 different IF
bandwidths. U3741BM-M2, the version with
B
IF
= 300 kHz, is well suited for ASK systems where the
TEMIC PLL transmitter U2741B is used. The receiver
U3741BM
-
M3 employs an IF bandwidth of
f
IF
= 600 kHz. This version can be used together with the
U2741B in FSK and ASK mode. If used in ASK
applications, it allows higher tolerances for the receiver
and PLL transmitter crystals. SAW transmitters exhibit
much higher transmit frequency tolerances compared to
PLL transmitters. Generally, it is necessary to use
B
IF
= 600 kHz together with such transmitters.