MT8841
Functional Description
IN+
The MT8841 Calling Number Identification Circuit
(CNIC) is a device compatible with the Bellcore
proposal (TR-NWT-000030) on generic requirements
for transmitting asynchronous voiceband data to
Customer Premises Equipment (CPE) from a serving
Stored Program Controlled Switching System
(SPCS) or a Central Office (CO). This data
transmission technique is applicable in a variety of
services like Calling Number Delivery (CND), Calling
Name Delivery (CNAM) or Calling Identity Delivery
on Call Waiting (CIDCW) as specified in Custom
Local Area Signalling Service (CLASS
SM
) calling
information delivery features by Bellcore.
With CND, CNAM and CIDCW service, the called
subscriber has the capability to display or to store
the information on the calling party which is sent by
the CO and received by the CNIC.
In the CND service, information about a calling party
is embedded in the silent interval between the first
and second ring. During this period, the CNIC
receives and demodulates the 1200 baud FSK signal
(compatible with Bell-202 specification) and outputs
data into a 3-wire serial interface.
In the CIDCW service, information about a second
calling party is sent to the subscriber, while they are
engaged in another call. During this period, the CNIC
receives and demodulates the FSK signal as in the
CND case.
The CNIC is designed to provide the data
transmission interface required for the above service
C
R
IN
IN-
R
F
GS
VOLTAGE GAIN
(A
V
) = R
F
/ R
IN
V
Ref
MT8841
Figure 4 - Single-Ended Input Configuration
at the called subscriber location either in the on-hook
case as in CND, or the off-hook case, as in
CIDCW. The functional block diagram of the CNIC
is shown in Figure 1. Note however, for CIDCW
applications, a separate CAS (CPE Alerting Signal)
detector is required.
In Europe, Caller ID and CIDCW services are being
proposed. These schemes may be different from
their North American counterparts. In most cases,
1200 baud CCITT V.23 FSK is used instead of Bell
202. Because the CNIC can also demodulate 1200
baud CCITT V.23 with the same performance, it is
suitable for these applications.
Although the main application of the CNIC is to
support CND and CIDCW service, it may also be
used in any application where 1200 baud Bell 202
and/or CCITT V.23 FSK data reception is required.
Input Configuration
The input arrangement of the MT8841 provides an
operational amplifier, as well as a bias source (V
Ref
)
which is used to bias the inputs at V
DD/2
. Provision is
made for connection of a feedback resistor to the op-
amp output (GS) for adjustment of gain. In a single-
ended configuration, the input pins are connected as
shown in Figure 4.
Figure 3 shows the necessary connections for a
differential input configuration.
C1
R1
IN+
IN-
C2
R4
R5
GS
R3
R2
V
Ref
DIFFERENTIAL INPUT AMPLIFIER
C1 = C2 = 10 nF
R1 = R4 = R5 = 100 kΩ
R2 = 60kΩ, R3 = 37.5 kΩ
R3 = (R2R5) / (R2 + R5)
VOLTAGE GAIN
(A
V
diff) = R5/R1
INPUT IMPEDANCE
(Z
IN
diff) = 2
R1
2
+ (1/ωC)
2
MT8841
User Interface
The CNIC provides a powerful 3-pin interface which
can reduce the external hardware and software
requirements. The CNIC receives the FSK signal,
demodulates it, and outputs the extracted data to the
DATA pin. For each received stop bit start bit
sequence, the CNIC outputs a fixed frequency clock
string of 8 pulses at the DCLK pin. Each clock rising
5-13
Figure 3 - Differential Input Configuration
MITEL [ MITEL NETWORKS CORPORATION ]
