Tone Detector
9
MX105A PRELIMINARY INFORMATION
5.9 Calculate Maximum De-response Time
TOFF
≈
−3
×
ln
VTH
VINMAX
R3 × C3 A
where: VTH 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
mVRMS. This graph is for VDD = 5V; for lower VDD KDT increases.
TOFF ≈ KDT × R3 × C3A
3.8
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 (mVRMS)
Figure 4: KDT Factor for TOFF vs. Signal Input Amplitude
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