T5744 ATMEL [ATMEL Corporation], T5744 Datasheet - Page 3

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

Figure 3. Block Diagram
RF Front End
4521B–RKE–01/03
LNAGND
MIXVCC
LNA_IN
CDEM
AVCC
AGND
DGND
RSSI
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
Oscillator) generates the drive voltage frequency f
the voltage at Pin LF. f
f
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
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
hereby of f
of the crystal and the XTO must be considered.
XTO
LNA
by the phase frequency detector. The current output of the phase frequency detec-
f
XTO
XTO
BR_0
and data filter
= f
LO
Demodulator
RSSI IF Amp
4. Order
. If f
IF Amp
. When designing the system in terms of receiving bandwidth, the accuracy
ASK-
3 MHz
3 MHz
LO
LPF
LPF
/64
BR_1
RSSI
LO
is determined, f
Dem_out
LO
is divided by factor 64. The divided frequency is compared to
f
VCO
64
XTO
Data interface
Standby logic
can be calculated using the following formula:
Test
XTO
LO
for the mixer. f
XTO
DATA
TEST
MODE
DVCC
ENABLE
LFGND
LFVCC
XTO
LF
. The VCO (Voltage-Controlled
LO
is dependent on
T5744
LO
XTO
/64 is
and
3