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Электронный компонент: T5743P3-TGQ

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1
Features
Two Different IF Receiving Bandwidth Versions Are Available (B
IF
= 300 kHz or 600 kHz)
5 V to 20 V Automotive Compatible Data Interface
IC Condition Indicator, Sleep or Active Mode
Low Power Consumption Due to Configurable Self Polling with a Programmable
Timeframe Check
High Sensitivity, Especially at Low Data Rates
Data Clock Available for Manchester- and Bi-phase-coded Signals
Minimal External Circuitry Requirements, no RF Components on the PC Board Except
Matching to the Receiver Antenna
Sensitivity Reduction Possible Even While Receiving
Fully Integrated VCO
SO20 Package
Supply Voltage 4.5 V to 5.5 V, Operating Temperature Range -40C to +105C
Single-ended RF Input for Easy Adaptation to
/4 Antenna or Printed Antenna on PCB
Low-cost Solution Due to High Integration Level
ESD Protection According to MIL-STD. 883 (4KV HBM)
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 State-of-the-art SAWs.
Communication to Microcontroller Possible Via a Single, Bi-directional Data Line
Power Management (Polling) Is Also Possible by Means of a Separate Pin Via the
Microcontroller
Programmable Digital Noise Suppression
Description
The T5743 is a multi-chip PLL receiver device supplied in an SO20 package. It has
been especially developed for the demands of RF low-cost data transmission systems
with data rates from 1 kBaud to 10 kBaud in Manchester or Bi-phase code. The
receiver is well suited to operate with Atmel's 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.
System Block Diagram
Figure 1. System Block Diagram
Demod.
IF Amp
LNA
VCO
PLL
XTO
Control
T5743
1...5
C
Power
amp.
XTO
VCO
PLL
U2741B
Antenna
Antenna
UHF ASK/FSK
Remote control transmitter
UHF ASK/FSK
Remote control receiver
UHF ASK/FSK
Receiver
T5743
Preliminary
Rev. 4569ARKE12/02
2
T5743
4569ARKE12/02
Pin Configuration
Figure 2. Pinning SO20
1
2
3
4
5
6
7
8
10
9
19
18
17
16
14
15
13
12
11
20
AVCC
TEST
AGND
MIXVCC
LNAGND
LNA_IN
IC_ACTIVE
CDEM
DATA_CLK
MODE
XTO
LFGND
LF
POLLING/_ON
DGND
n.c.
LFVCC
DATA
DVCC
SENS
T5743
Pin Description
Pin
Symbol
Function
1
SENS
Sensitivity-control resistor
2
IC_ACTIVE
IC condition indicator
Low = sleep mode
High = active mode
3
CDEM
Lower cut-off frequency data filter
4
AVCC
Analog power supply
5
TEST
Test pin, during operation at GND
6
AGND
Analog 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
3
T5743
4569ARKE12/02
Figure 3. Block Diagram
15
DVCC
Digital power supply
16
MODE
Selecting 433.92 MHz/315 MHz
Low: f
XT0
= 4.90625 MHz (USA)
High: f
XT0
= 6.76438 MHz (Europe)
17
DATA_CLK
Bit clock of data stream
18
DGND
Digital ground
19
POLLING/_ON
Selects polling or receiving mode
Low: receiving mode
High: polling mode
20
DATA
Data output/configuration input
Pin Description (Continued)
Pin
Symbol
Function
FSK/ASK-
Demodulator
and data filter
IF Amp
IF Amp
4. Order
LPF
3 MHz
LPF
3 MHz
Dem_out
Limiter out
RSSI
Sensitivity
reduction
Standby logic
Polling circuit
and
control logic
FE
CLK
VCO
XTO
64
f
CDEM
AVCC
SENS
AGND
DGND
MIXVCC
LNAGND
LNA_IN
DATA
POLLING/_ON
TEST
DATA_CLK
MODE
LFGND
LFVCC
XTO
LF
DVCC
LNA
IC_ACTIVE
Data
interface
4
T5743
4569ARKE12/02
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 an 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 detec-
tor 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 crys-
tal. 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.
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 bit
check may no longer be possible since f
LO
cannot settle in time before the bit check
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 follow-
ing 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 fre-
quencies, 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.
DVCC
XTO
LF
LFVCC
LFGND
V
C
C10
R1
C9
S
L
V
S
R1 = 820
W
C9 = 4.7 nF
C10 = 1 nF
5
T5743
4569ARKE12/02
This is described by the following formulas:
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 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
D
P
Ref
= 40 dB can be achieved. There are SAWs available that exhibit a notch at
D
f = 2 MHz. These SAWs work best for an intermediate frequency of f
IF
= 1 MHz. The
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
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 net-
works 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
365 MHz < f
RF
< 450 MHz,
MODE = 1
MODE
0 (USA) : f
IF
f
LO
314
----------
=
=
MODE
1 (Europe) : f
IF
f
LO
432.92
------------------
=
=
f
LO
f
RF
1
1
314
----------
+
-------------------
=
f
IF
f
LO
314
----------
=
f
LO
f
RF
1
1
432.92
------------------
+
----------------------------
=
f
IF
f
LO
432.92
------------------
=