XR-2211 Datasheet, PDF (11/24 Pages) Exar Corporation – FSK Demodulator/ Tone Decoder

XR-2211
f) The input to the XR-2211 may sometimes be too sensitive to noise conditions on the input line. Figure 4 illustrates
a method of de-sensitizing the XR-2211 from such noisy line conditions by the use of a resistor, Rx, connected
from pin 2 to ground. The value of Rx is chosen by the equation and the desired minimum signal threshold level.
ǒ Ǔ V_IN
minimum
(peak) +
V_a–V_b + DV " 2.8mV
offset
+
V_REF
20, 000
(20, 000 )
R_X)
or
R_X + 20, 000
V_REF
DV
–1
V_IN minimum (peak) input voltage must exceed this value to be detected (equivalent to adjusting V threshold)
V_CC
Input
ÎÎ Va
2
Rx
20K
ÎÎÎÎ _{VREF 10}
To Phase
Detector
Vb
20K
Figure 4. Desensitizing Input Stage
g) Calculate Data Filter Capacitance, C_F:
R_sum
+
(R_F ) R₁)·R_B
(R₁ ) R_F ) R_B)
C_F
+
0.25
(R_sum·Baud
Rate)
Baud
rate
in
1
seconds
Note: All values except R₀ can be rounded to nearest standard value.
Rev. 3.01
11