Rainbow Electronics T5744 User Manual
Features
• Minimal External Circuitry Requirements, no RF Components on the PC Board Except
Matching to the Receiver Antenna
• High Sensitivity, Especially at Low Data Rates
• SSO20 and SO20 package
• Fully Integrated VCO
• Supply Voltage 4.5 V to 5.5 V, Operating Temperature Range -40°C to 105°C
• Single-ended RF Input for Easy Adaptation to l/4 Antenna or Printed Antenna on PCB
• Low-cost Solution Due to High Integration Level
• Various Types of Protocols Supported (i.e., PWM, Manchester and Biphase)
• Distinguishes the Signal Strength of Several Transmitters via RSSI (Received Signal
Strength Indicator)
• 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 Newer SAWs
• Power Management (Polling) is Possible by Means of a Separate Pin via the
Microcontroller
• Receiving Bandwidth BIF = 600 kHz
UHF ASK
Receiver
T5744
Description
The T5744 is a PLL receiver device for the receiving range of f0= 300 MHz to
450 MHz. It is developed for the demands of RF low-cost data communication systems with low data rates and fits for most types of modulation schemes including
Manchester, Biphase and most PWM protocols. Its main applications are in the areas
of telemetering, security technology and keyless-entry systems.
Figure 1. System Block Diagram
1 Li cell
Keys
Encoder
M44Cx9x
UHF ASK/FSK
Remote control transmitter
U2741B
PLL
XTO
VCO
Power
amp.
T5744
Antenna Antenna
LNA VCO
UHF ASK
Remote control receiver
Demod.
IF Amp
PLL XTO
Data
interface
1...3
µC
Preliminary
Rev. 4521A–RKE–02/02
1
Pin Configuration
Figure 2. Pinning SO20 and SSO20
Pin Description
Pin Symbol Function
1 BR_0 Baud rate select LSB
2 BR_1 Baud rate select MSB
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
9LNA_INRF 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
17 RSSI Output of the RSSI amplifier
18 TEST Test pin, during operation at GND
19 ENABLE
20 DATA Data output
DATA
20
19
2
1
BR_1
BR_0
RSSI
MODE
18
3
CDEM
16
17
4
5
AVCC
AGND
TEST
ENABLE
Selecting 433.92 MHz /315 MHz
Low: 315 MHz (USA)
High: 433.92 MHz (Europe)
Selecting operation mode
Low: sleep mode
High: receiving mode
DVCC
T5744
6
DGND
XTO
141513
7
MIXVCC
LF
LFGND
8
LNAGND
LFVCC
12
11
9
10
n.c.
LNA_IN
2
T5744
4521A–RKE–02/02
Figure 3. Block Diagram
T5744
BR_0 BR_1
CDEM
RSSI
AVCC
AGND
DGND
MIXVCC
LNAGND
LNA_IN
LNA
ASK-
Demodulator
and data filter
RSSI
RSSI IF Amp
4. Order
LPF
3 MHz
IF Amp
LPF
3 MHz
Dem_out
Data interface
Test
Standby logic
VCO XTO
f
64
DATA
TEST
MODE
DVCC
ENABLE
LFGND
LFVCC
XTO
LF
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
. The VCO (Voltage-Controlled
XTO
for the mixer. fLO is dependent on
LO
LO
XTO
/64 is
and
4521A–RKE–02/02
(crystal oscillator) generates the reference frequency f
Oscillator) generates the drive voltage frequency f
the voltage at Pin LF. f
by the phase frequency detector. The current output of the phase frequency detec-
f
XTO
is divided by factor 64. The divided frequency is compared to
LO
tor is connected to a passive loop filter and thereby generates the control voltage VLF
for the VCO. By means of that configuration, VLF is controlled in a way that f
equal to f
f
XTO
. If fLO is determined, f
XTO
= fLO/64
can be calculated using the following formula:
XTO
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
hereby of f
. When designing the system in terms of receiving bandwidth, the accuracy
LO
of the crystal and the XTO must be considered.
3
Figure 4. PLL Peripherals
DVCC
XTO
V
S
C
L
LFGND
R1 = 820 Ω
C9 = 4.7 nF
LF
LFVCC
R1
V
S
C9
C10 = 1 nF
C10
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
is determined by the RF input frequency fRF and the IF frequency fIF using the follow-
f
LO
ing formula:
= fRF - f
f
LO
IF
To determine fLO, the construction of the IF filter must be considered at this point. The
nominal IF frequency is f
quencies, the filter is tuned by the crystal frequency f
fixed relation between f
= 1 MHz. To achieve a good accuracy of the filter’s corner fre-
IF
and fLO that depends on the logic level at pin mode. This is
IF
. This means that there is a
XTO
described by the following formulas:
MODE = 0 USA f
MODE = 1 Europe f
The relation is designed to achieve the nominal IF frequency of f
applications. For applications where f
case of f
= 433.92 MHz, MODE must be set to ’1’. For other RF frequencies, fIF is
RF
not equal to 1 MHz. f
= fLO/314
IF
= fLO/432.92
IF
= 1 MHz for most
= 315 MHz, MODE must be set to ’0’. In the
RF
is then dependent on the logical level at Pin MODE and on fRF.
IF
IF
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 T5744 exhibits its highest sensitivity at the best signal-tonoise 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
∆P
= 40 dB can be achieved. There are SAWs available that exhibit a notch at
Ref
∆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 applications, a SAW is used.
4
T5744
4521A–RKE–02/02
Figure 5 shows a typical input matching network for fRF = 315 MHz and fRF =
433.92 MHz using a SAW. Figure 6 illustrates the input matching to 50
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
= 315 MHz, MODE = 0 fLO = 314 MHz fIF = 1 MHz
f
RF
f
= 433.92 MHz, MODE = 1 fLO = 432.92 MHz fIF = 1 MHz
RF
T5744
Ω without a
300 MHz < f
365 MHz < f
< 365 MHz, MODE = 0
RF
< 450 MHz, MODE = 1
RF
f
LO
f
LO
Figure 5. Input Matching Network with SAW Filter
8
LNAGND
T5744
C3
22p
fRF = 433.92 MHz
L
25n
9
C16
100p
LNA_IN
L3
27n
C17
8.2p
TOKO LL2012
F27NJ
f
RF
-------------------= f
1
1
--------- -+
314
f
RF
--------------------------- -= f
1
1
----------------- -+
432.92
C3
47p
L
25n
fRF = 315 MHz
f
RF
--------- -=
IF
314
f
RF
----------------- -=
IF
432.92
8
LNAGND
T5744
9
LNA_IN
C16
100p
L3
47n
C17
22p
TOKO LL2012
F47NJ
RF
IN
4521A–RKE–02/02
C2
8.2p
L2
TOKO LL2012
F33NJ
33n
1
2
IN
IN_GND
B3555
CASE_GND
3,4 7,8
OUT
OUT_GND
L2
C2
10p
TOKO LL2012
F82NJ
82n
1
2
IN
IN_GND
B3551
CASE_GND
3,4 7,8
OUT
OUT_GND
5
6
RF
5
6
IN
5
Figure 6. Input Matching Network without SAW Filter
fRF = 433.92 MHz
C3
15p
RF
IN
3.3p
22n
25n
100p
TOKO LL2012
F22NJ
8
9
Please note that for all coupling conditions (see Figure 5 and Figure 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
LNAGND
T5744
LNA_IN
fRF = 315 MHz
C3
33p
RF
IN
3.3p
39n
25n
100p
TOKO LL2012
F39NJ
8
9
LNAGND
T5744
LNA_IN
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
= 433.92 MHz is used. For other RF input frequencies, refer to Table 1 to determine
f
RF
the center frequency.
The receiver T5744 employs an IF bandwidth of B
together with the U2741B in ASK mode.
= 1 MHz for applications where fRF = 315 MHz or
IF
= 600 kHz and can be used
IF
RSSI Amplifier The subsequent RSSI amplifier enhances the output signal of the IF amplifier before it is
fed into the demodulator. The dynamic range of this amplifier is DRRSSI = 60 dB. If the
RSSI amplifier is operated within its linear range, the best S/N ratio is maintained. If the
dynamic range is exceeded by the transmitter signal, the S/N ratio is defined by the ratio
of the maximum RSSI output voltage and the RSSI output voltage due to a disturber.
The dynamic range of the RSSI amplifier is exceeded if the RF input signal is about
60 dB higher compared to the RF input signal at full sensitivity.
Pin RSSI The output voltage of the RSSI amplifier (VRSSI) is available at Pin RSSI. Using the
RSSI output signal, the signal strength of different transmitters can be distinguished.
The usable input power range P
Since different RF input networks may exhibit slightly different values for the LNA gain,
the sensitivity values given in the electrical characteristics refer to a specific input
matching. This matching is illustrated in Figure 6 and exhibits the best possible
sensitivity.
is -100 dBm to -55 dBm.
Ref
6
T5744
4521A–RKE–02/02
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