XR2211 Exar Corporation, XR2211 Datasheet - Page 15

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

FSK Decoding with Carrier Detect
The lock detect section of XR-2211 can be used as a
carrier detect option for FSK decoding.
recommended circuit connection for this application is
shown in Figure 11. The open collector lock detect output,
pin 6, is shorted to data output (pin 7). Thus, data output
will be disabled at “low” state, until there is a carrier within
the detection band of the PLL and the pin 6 output goes
“high” to enable the data output.
Note: Data Output is “Low” When No Carrier is Present.
The minimum value of the lock detect filter capacitance
C
This is the range of incoming frequencies over which the
loop can acquire lock and is always less than the tracking
range. It is further limited by C
> f/2. For R
of C
With values of C
observed on the lock detect output as an incoming signal
D
is inversely proportional to the capture range, + fc.
D
C in F and f in Hz.
Rev. 3.01
can be determined by:
Tone
Input
C
D
D
0.1 F
= 470K , the approximate minimum value
16
D
f
2
that are too small, chatter can be
C in F and f in Hz.
1
. For most applications, fc
Detect
Phase
Detect
Phase
Quad
Loop
Figure 12. Circuit Connection for Tone Detection
14
VCO
50nF
11
C
0
13
470K
5%
R
C
220pF
5%
12
D
1
The
3
20K
R
200K
1%
R
1%
Rx
5K
1
0
15
V
0.1 F
CC
80nF
C
frequency
Excessively large values of C
of the lock detect output. For Caller I.D. applications
choose C
Tone Detection
Figure 12 shows the generalized circuit connection for
tone detection. The logic outputs, LDOQN and LDOQ at
pins 5 and 6 are normally at “high” and “low” logic states,
respectively. When a tone is present within the detection
band of the PLL, the logic state at these outputs become
reversed for the duration of the input tone. Each logic
output can sink 5mA of load current.
Both outputs at pins 5 and 6 are open collector type
stages, and require external pull-up resistors R
R
With reference to Figure 3 and Figure 12 , the functions of
the external circuit components can be explained as
follows: R
detection bandwidth; C
constant and the loop damping factor.
VCO
Fine
Tune
D
L3
, as shown in Figure 12.
10
8
D
0
Detect
Comp.
+
+
Lock
and C
= 0.1 F.
approaches
Reference
Comp.
Internal
FSK
6 LDOQ
5 LDOQN
7
0
set VCO center frequency; R
1
V
sets the low pass-loop filter time
CC
5.1K
RL2
the
D
will slow the response time
Logic Output
XR-2211
5.1K
RL3
capture
bandwidth.
1
sets the
L2
and