u3742bm ATMEL Corporation, u3742bm Datasheet - Page 4

• Manufacturer Part Number: u3742bm
• Description: Uhf Ask/fsk Receiver
• Manufacturer: ATMEL Corporation

Pin Description (Continued)
RF Front End
4
Pin
16
17
18
19
20
U3742BM
ENABLE
Symbol
MODE
TEST
DATA
RSSI
Function
Selecting 433.92 MHz/315 MHz
Low: 4.90625 MHz (USA)
High: 6.76438 (Europe)
Output of the RSSI amplifier
Test pin, during operation at GND
Enables the polling mode
Low: polling mode off (sleep mode)
High: polling mode on (active mode)
Data output/configuration input
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 2 on page 2, 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
oscillator) generates the drive voltage frequency f
the voltage at pin LF. f
to f
detector is connected to a passive loop filter and thereby generates the control voltage
V
equal to f
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 the 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.
Figure 4. PLL Peripherals
XTO
LF
XTO
for the VCO. By means of that configuration, V
= f
LO
by the phase frequency detector. The current output of the phase frequency
/64
XTO
LO
. If f
. When designing the system in terms of receiving bandwidth, the accuracy
LO
is determined, f
LO
is divided by a factor of 64. The divided frequency is compared
LFGND
LFVCC
DVCC
XTO
LF
XTO
V
V
S
S
can be calculated using the following formula:
C
R
9
1
C
C
10
LO
LF
L
is controlled in a way that f
for the mixer. f
XTO
R
C
C
1
10
9
. The VCO (voltage-controlled
= 820 Ω
= 4.7 nF
= 1 nF
LO
is dependent on
4735A–RKE–11/03
LO
XTO
/64 is
and