CPC5604 Datasheet, PDF (17/33 Pages) Clare, Inc. – Optical Data Access Arrangement I.C.

CPC5604
Ring Signal Detection
The snoop circuit actively monitors the telephone line
for 2 conditions:
1. Incoming ring signal
2. Caller ID information
Figure 2D Connection To Host Single Ended
(Transmit)
HOST DATA PUMP/CODEC
CPC5604A LITELINK^TM
TXA1
TXA2
0.1uf _TX-
-
+
TX+
0.1uf
SINGLE ENDED CONNECTION TO CPC5604A
The Snoop circuit “snoops” the line continuously while
the LiteLink^TM is in the on-hook mode. Current taken
from the telephone line in the on-hook condition by the
LITELINK^TM is maintained at a low 2uA maximum thus
meeting regulatory requirements for minimum on-hook
impedance limitation. When the central office places
the ring signal on the telephone line, that signal is cou-
pled through a pair of RC circuits to a differential ampli-
fier in the LiteLink^TM.
Referring to Block Diagram, snoop capacitors connect-
ed to the SNP1/SNP2 pins provide a high voltage isola-
tion barrier between the host and the telephone line
while coupling the AC signals to the snoop amplifier.
The ring signal is digitized and brought out to the RING
pin where the host can qualify it as a valid ring signal.
The ring detection threshold is dependent on the values
of 3 external components: RRXF (R3), RSNOOP (R5 or
R6), and CS (C6 or C7). The default values in the typi-
cal bill of materials reflects the parameters in the data
sheet for typical operation. If it is desired to change the
threshold, the values can be selected by using the
equation:
V_RING(PEAK) = 330E-3
5R_RXF
(R_SNOOP)² + 1
(2πf C_S)²
Care should be taken when using this equation since
RRXF (R3), CS (C6 or C7), and RSNOOP (R5 or R6)
affect receive gain and Caller ID gain. It is recom-
mended that RRXF (R3) be set to the typical value and
then after adjusting the ring detect threshold, check that
CID gain is acceptable.
Caller ID Detection
Caller ID (CID) is a service offered by the telephone
company to provide caller information (i.e. caller’s tele-
phone number) to the called party. CID service is
optional and signals only appear on the telephone lines
of subscribers that pay for this feature. The CID infor-
mation appears on the telephone line after the first ring
burst is sent from the central office (CO).
Some of the characteristics of the CID signal are sum-
marized below:
Parameter
Signal Level
Link Type
Transmission Scheme
Logical 1 (mark)
Logical 0 (Space)
Transmission Rate
Data
BER
Bit Duration
Value
-13dBm
Simplex, 2W
Phase-coherent, FSK
1200±12Hz
2200± 22Hz
1200bps
serial binary async
< 10E -5
833±50uS (same for start/stop as
well)
Full details about the CID signal can be found in Bellcore
document TR-TSY-000030, issue 1/1988.
Figure 2.7.A shows the CID timing diagram. Waveform
#1 represents the Analog signals on the telephone line
(amplitude not drawn to scale), waveform #2 is the dig-
ital RING detect output from the LiteLink^TM, waveform
#3 is the CID input to the LiteLink^TM from the Host. After
the first ring burst is detected by the host, the host
enables the CID line which automatically couples the
snoop circuit to the RX outputs on the LiteLink^TM.
Where f = ring frequency typically 20Hz.
XXX
www.clare.com
17