XR2211 Exar Corporation, XR2211 Datasheet - Page 10

• Manufacturer Part Number: XR2211
• Description: FSK Demodulator/ Tone Decoder
• Manufacturer: Exar Corporation

APPLICATIONS INFORMATION
FSK Decoding
Figure 10 shows the basic circuit connection for FSK decoding. With reference to Figure 3 and Figure 10 , the functions
of external components are defined as follows: R
and C
the FSK data output. The resistor R
facilitate rapid transition between output logic states.
Design Instructions:
The circuit of Figure 10 can be tailored for any FSK decoding application by the choice of five key circuit components: R
R
follows:
(All resistance in
a) Calculate PLL center frequency, f
b) Choose value of timing resistor R
c) Calculate value of C0 from design equation (1) or from Figure 7 :
d) Calculate R1 to give the desired tracking bandwidth (See design equation 5).
e) Calculate C1 to set loop damping. (See design equation 4):
XR-2211
1
, C
value is R
Normally, = 0.5 is recommended.
Rev. 3.01
0
1
, C
sets the loop filter time constant and the loop damping factor. C
1
f
R
C
R
C
and C
O
O
O
1
1
0
= 20K . The final value of R
F
( f
1250· C
F
R
R
R
. For a given set of FSK mark and space frequencies, f
R
1
1
O
0
0
–f
· F
1
1
’s, all frequency in Hz and all capacitance in farads, unless otherwise specified)
· f
· f
·
2
0
2
)
0
R
2
2
·2
0
X
B
0
, to be in the range of 10K to 100K . This choice is arbitrary. The recommended
O
from pin 7 to pin 8 introduces positive feedback across the FSK comparator to
:
0
is normally fine-tuned with the series potentiometer, R
0
and C
0
set the PLL center frequency, R
10
F
O
and R
and f
1
F
, these parameters can be calculated as
form a one-pole post-detection filter for
1
sets the system bandwidth,
X
.
0
,