XR2211 Exar Corporation, XR2211 Datasheet - Page 18

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

Linear FM Detection
XR-2211 can be used as a linear FM detector for a wide
range
applications. The recommended circuit connection for
this application is shown in Figure 13. The demodulated
output is taken from the loop phase detector output (pin
11), through a post-detection filter made up of R
and an external buffer amplifier. This buffer amplifier is
necessary because of the high impedance output at pin
11. Normally, a non-inverting unity gain op amp can be
used as a buffer amplifier, as shown in Figure 13.
XR-2211
Ground
V
+
1
Rev. 3.01
4
of
20K
20K
analog
2K
A
Internal Voltage
Reference
Voltage Controlled
R
Oscillator
0
communications
13
Capacitor
B
Timing
Resistor
Timing
C 0 14
B’
12
Voltage
Output
REF
10
8K
2K
A’
Input
2
10K
Input Preamplifier
Figure 14. Equivalent Schematic Diagram
and Limiter
and
10K
From
VCO
telemetry
A
A’
F
and C
Loop Phase Detector
F
From
VCO
,
B
B’
18
The FM detector gain, i.e., the output voltage change per
unit of FM deviation can be given as:
where VR is the internal reference voltage (V
- 650mV). For the choice of external components R
C
D
, C
1
and C
Phase Detector
Quadrature
F
, see the section on design equations.
V
11
OUT
Loop
Output
Detector
R
100· R
Lock
Comparator
Input
Filter
FSK
1
Detect
· V
FSK Comparator
REF
3
0
8
Lock Detect
Comparator
REF
FSK
Data
Output
7
= V
Lock Detect
Outputs
1
CC
, R
6
5
/2
0
,