Preliminary W91030B
DD
SS
DD
SS
capacitor charging from V to V (the ALGRC pin charges from V to V through a resistor). The
capacitor will charge rapidly via a charge switch after ALGO returns low. To obtain unequal present
and absent guard times, a diode can be connected as shown in Figure 7-6, to give the unequal
resistance required during capacitor charging and discharging.
W91030B
VDD
VDD
Dual tone detected
Discharge
Switch
Capacitor
Charge/Discharge
Control Circuit
C
ALGRC
+
-
CPth
V
Comparator
R
Charge
Switch
ALGR
ALGO
Figure 7-4. Guard Time Circuit of Dual Tone Alert Signal Detection
Tip/Ring
ALGR
Alerting Signal
t DA
tDP
tGP
tGA
ALGRC
ALGO
VCPth
VCPth
tREC
tABS
Discharge
Switch
ON
Charge
Switch
ON
ON
Figure 7-5. Guard Time Waveform of ALGR, ALGRC and ALGO pins
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