SM8223A Datasheet, PDF (10/15 Pages) Nippon Precision Circuits Inc – FSK Decoder and DTMF Receiver IC

SM8223A
VRIG
VDD
0.7VDD
VSS
0.3VDD
Point a Signal
VRIG
VDD
0.7VDD
VSS
0.3VDD
Point b Signal
VDD
0.7VDD
VSS
0.3VDD
Point c Signal
VDD
0.7VDD
VSS
0.3VDD
Point d Signal
Figure 2. Ring signal detector circuit waveform transitions
The voltage divider level and RC time constant are
given by the following equations, respectively.
0.7V _DD
=
--------------^R---¹---------------
R₁ + R₂ + R₃
⋅
V
RIG
C₁R₄=
------------------^t-------------------
I

n

V^-----_D^--V--_D^{---D--–--D---}V^----_T^--_{}
where t is the guard time, and the trigger level satis-
fies the expression 0.3V_DD ≤ V_T ≤ 0.7V_DD.
NIPPON PRECISION CIRCUITS—10