cf8223a Nippon Precision Circuits Inc, (NPC), cf8223a Datasheet - Page 8

• Manufacturer Part Number: cf8223a
• Description: Fsk Decoder And Dtmf Receiver Ic
• Manufacturer: Nippon Precision Circuits Inc, (NPC)

FUNCTIONAL DESCRIPTION
Ring Signal Detector
The telephone tip and ring signals pass through a
protection circuit and are input to a resistor, capaci-
tor and diode bridge network, shown in figure 1.
The diode bridge full-wave rectified output signal
(point a) is reduced in level by a resistor voltage
divider comprising R
input on RDIN. When the ring signal input on RDIN
exceeds the Schmitt buffer trigger voltage (0.7V
the output switches the open-drain RDRC pin. The
signal at RDRC (point c) drives a time-constant cir-
RING
TIP
1
and R
C2
C2
2
(point b), and then
R3
R3
Figure 1. Ring signal detector circuit
Db
c
a
DD
CF8223A
),
R4
C1
R2
D1
cuit comprised by resistor R
nected to the input of a second Schmitt buffer to
generate the detector signal output on RDET (point
d). Thus, RDET goes LOW when the ring or tip sig-
nal exceeds the level set by the resistor voltage
divider.
R1
d
RDRC
RDET
RDIN
b
NIPPON PRECISION CIRCUITS INC.—8
4
and capacitor C
1
con-