Rainbow Electronics MAX1471 - Manual (Page 13)

Choosing standard capacitor values changes C F1 to
470pF and C F2 to 220pF. In the Typical Application
Circuit, C F1 and C F2 are named C4 and C3, respective-
ly, for ASK data, and C21 and C22 for FSK data.
Data Slicers
The purpose of a data slicer is to take the analog output
of a data filter and convert it to a digital signal. This is
achieved by using a comparator and comparing the ana-
log input to a threshold voltage. The threshold voltage is
set by the voltage on the DSA- pin for the ASK receive
chain (DSF- for the FSK receive chain), which is connect-
ed to the negative input of the data slicer comparator.
Numerous configurations can be used to generate the
data-slicer threshold. For example, the circuit in Figure
4 shows a simple method using only one resistor and
one capacitor. This configuration averages the analog
output of the filter and sets the threshold to approxi-
mately 50% of that amplitude. With this configuration,
the threshold automatically adjusts as the analog signal
varies, minimizing the possibility for errors in the digital
data. The sizes of R and C affect how fast the threshold
tracks to the analog amplitude. Be sure to keep the cor-
ner frequency of the RC circuit much lower than the
lowest expected data rate.
C
k kHz
pF
C
k kHz
pF
F1
F2
=
( )( )( )( )
≈
=
( )( )( )( )
≈
1 000
1 414 100 3 14 5
450
1 414
4 100 3 14 5
225
.
. .
.
.
Ω
Ω
MAX1471
315MHz/434MHz Low-Power, 3V/5V
ASK/FSK Superheterodyne Receiver
______________________________________________________________________________________ 13
Table 1. Component Values for Typical Application Circuit
COMPONENT VALUE FOR 433.92MHz RF VALUE FOR 315MHz RF DESCRIPTION (%)
C3 220pF 220pF 10
C4 470pF 470pF 5
C5 0.047µF 0.047µF 10
C6 0.1µF 0.1µF 10
C7 100pF 100pF 5
C8 100pF 100pF 5
C9 1.0pF 2.2pF ±0.1pF
C10 220pF 220pF 10
C11 100pF 100pF 5
C12 1500pF 1500pF 10
C14 15pF 15pF 5
C15 15pF 15pF 5
C21 220pF 220pF 10
C22 470pF 470pF 5
C23 0.01µF 0.01µF 10
C26 0.1µF 0.1µF 10
C27 0.047µF 0.047µF 10
L1 56nH 100nH Coilcraft 0603CS
L2 16nH 30nH Coilcraft 0603CS
L3 10nH 15nH 5
R3 25k Ω 25k Ω 5
R8 25k Ω 25k Ω 5
Y1 13.2256MHz 9.509MHz Crystal
Y2 10.7MHz ceramic filter 10.7MHz ceramic filter Murata SFECV10.7 series
Note: Component values vary depending on PC board layout.