XR-2211 Datasheet, PDF (17/24 Pages) Exar Corporation – FSK Demodulator/ Tone Decoder

XR-2211
c) Calculate R₁ to set the bandwidth +Df (See design equation 5):
R₁
+
R₀·f_O·2
Df
+
20,
000·1,
100
000·2
+
400K
Note: The total detection bandwidth covers the frequency range of f_O +Df
d) Calculate value of C₀ for a given loop damping factor:
Normally, j = 0.5 is recommended.
C₁
+
1250·C₀
R₁·j²
+
1250·50·10^–9
400, 000·0.5²
+
6.25pF
Increasing C₁ improves the out-of-band signal rejection, but increases the PLL capture time.
e) Calculate value of the filter capacitor C_D . To avoid chatter at the logic output, with R_D = 470KW, C_D must be:
C_D
+
16
Df
w
16
200
w
80nF
Increasing C_D slows down the logic output response time.
f) Fine tune center frequency with 5KW potentiometer, R_X.
2
FM ^0.1µF
Input
Loop 11
Phase
Detect
C₁
VCO
12
14
Quad
Phase
Detect
13
C₀
V_CC
8
R₁
10
0.1µF
R₀
V_CC
R_F
100K
+
7
FSK
Comp
.
Internal
Reference
0.1µF
4
3+
C_{F 2}
1
11 LM324
Demodulated
Output
6
+
Lock ⁵
Detect
Comp.
LDOQ
LDOQN
Figure 13. Linear FM Detector Using XR-2211 and an External Op Amp.
(See Section on Design Equation for Component Values.)
Rev. 3.01
17