Tone Detector
9
MX105A PRELIMINARY INFORMATION
5.9 Calculate Maximum De-response Time
V
TH
T
OFF
≈ −
3
×
ln
V
IN
MAX
R3
×
C3
A
where: V
TH
is the detect filter sensitivity.
For improved de-response time, a diode (1N914 or similar) can be placed between pins 5 and 6, as shown in Figure 3.
The formula and figure below show the approximate time the MX105A will take to turn off after an in-band signal has been
removed. The effect of this diode is to greatly reduce the turn-off time with signal input amplitudes greater than 300
mV
RMS
. This graph is for V
DD
= 5V; for lower V
DD
KDT increases.
T
OFF
≈
K
DT
×
R3
×
C3
A
3.8
K
DT
= Number of RC Time Constants for
De-response with Diode
3.6
3.4
3.2
3.0
2.8
2.6
2.4
2.2
0
80
160
240
320
400
480
560
640
720
Input Signal Level (mV
RMS
)
Figure 4: K
DT
Factor for T
OFF
vs. Signal Input Amplitude
© 1997 MX•COM, INC.
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Doc.# 20480133.003
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