MAX1471_11 Datasheet, PDF (12/26 Pages) Maxim Integrated Products – 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver

315MHz/434MHz Low-Power, 3V/5V
ASK/FSK Superheterodyne Receiver
3.0V ^VDD
ASK DATA OUT
SCLK
DIO
C26
*
V_DD
CS
C5
R3
C4
C3
32 31 30 29 28 27 26 25
1
DSA-
2
DSA+
3
OPA+
4
DFA
C14
5
XTAL2
MAX1471
FSK DATA OUT
V_DD
24
DVDD
C23
23
DGND
22
DFF
21
OPF+
C22
C21
Y1
V_DD
C6
RF INPUT
C15
6
XTAL1
7
AVDD
L1
8
LNAIN
EXPOSED PAD
20
R8
DSF+
19
DSF-
C27
18
PDMAXF
17
*
PDMINF
C7
9 10 11
12
13 14 15 16
C11
C8
C9
C12
L3
V_DD
L2
C10
IN GND
OUT
Y2
*SEE LAST PARAGRAPH OF
PEAK DETECTORS SECTION
Figure 2. Typical Application Circuit
Data Filters
The data filters for the ASK and FSK data are imple-
mented as a 2nd-order lowpass Sallen-Key filter. The
pole locations are set by the combination of two on-
chip resistors and two external capacitors. Adjusting
the value of the external capacitors changes the corner
frequency to optimize for different data rates. The cor-
ner frequency in kHz should be set to approximately
1.5 times the fastest expected Manchester data rate in
kbps from the transmitter. Keeping the corner frequen-
cy near the data rate rejects any noise at higher fre-
quencies, resulting in an increase in receiver sensitivity.
The configuration shown in Figure 3 can create a
Butterworth or Bessel response. The Butterworth filter
offers a very flat amplitude response in the passband
and a rolloff rate of 40dB/decade for the two-pole filter.
The Bessel filter has a linear phase response, which
works well for filtering digital data. To calculate the
value of the capacitors, use the following equations,
along with the coefficients in Table 2:
C_F1
=
b
a₍100k₎₍π₎₍f_C)
C_F2
=
a
4₍100k₎₍π₎₍f_C)
where f_C is the desired 3dB corner frequency.
For example, choose a Butterworth filter response with
a corner frequency of 5kHz:
12 ______________________________________________________________________________________