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參數(shù)資料
| 型號： | MC33121P |
| 廠商： | MOTOROLA INC |
| 元件分類： | 模擬傳輸電路 |
| 英文描述： | LOW VOLTAGE SUBSCRIBER LOOP INTERFACE CIRCUIT |
| 中文描述： | TELECOM-SLIC, PDIP20 |
| 封裝： | PLASTIC, DIP-20 |
| 文件頁數(shù)： | 30/32頁 |
| 文件大小： | 570K |
| 代理商： | MC33121P |
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MC33121
30
MOTOROLA
HALF DUPLEX
— A transmission system which permits
communication in one direction at a time. CB radios, with
“push–to–talk” switches, and voice activated speaker-
phones, are half duplex.
HOOKSWITCH
— A switch, within the telephone, which con-
nects the telephone circuit to the subscriber loop. The name
derives from old telephones where the switch was activated
by lifting the receiver off and onto a hook on the side of the
phone.
HYBRID
— Another name for a two–to–four wire converter.
IDLE CHANNEL NOISE
— Residual background noise
when transmit and receive signals are absent.
LINE CARD
— The PC board and circuitry in the CO or PBX
which connects to the subscriber’s phone line. A line card
may hold circuitry for one subscriber, or a number of sub-
scribers.
LONGITUDINAL BALANCE
— The ability of the SLIC to
reject longitudinal signals on Tip and Ring.
LONGITUDINAL SIGNALS
— Common mode signals.
LOOP
— The loop formed by the two subscriber wires (Tip
and Ring) connected to the telephone at one end, and the
central office (or PBX) at the other end. Generally, it is a float-
ing system not referred to ground, or AC power.
LOOP CURRENT
— The DC current which flows through
the subscriber loop. It is typically provided by the central
office or PBX, and ranges from 20 to 120 mA.
OFF–HOOK
— The condition when the telephone is con-
nected to the phone system, permitting the loop current to
flow. The central office detects the DC current as an indica-
tion that the phone is busy.
ON–HOOK
— The condition when the telephone is discon-
nected from the phone system, and no DC loop current
flows. The central office regards an on–hook phone as avail-
able for ringing.
PABX
— Private Automatic Branch Exchange. In effect, a
miniature central office, it is a customer owned switching sys-
tem servicing the phones within a facility, such as an office
building. A portion of the PABX connects to the Bell (or other
local) telephone system.
PROTECTION, PRIMARY
— Usually consisting of carbon
blocks or gas discharge tubes, it absorbs the bulk of a light-
ning induced transient by clamping the voltages to less than
±
1500 V.
PROTECTION, SECONDARY
— Usually located on the line
card, it protects the SLIC and associated circuits from tran-
sient surges. Typically, it must be capable of clamping a
±
1.5 kV surge of 1.0 ms duration.
PULSE DIALING
— A dialing system whereby the loop cur-
rent is interrupted a number of times in quick succession.
The number of interruptions corresponds to the number
dialed, and the interruption rate is typically 10 per second.
The old rotary phones, and many new pushbutton phones,
use pulse dialing.
RECEIVE PATH
— Within the CO or PBX it is the speech
path from the internal switching system towards the phone
line (Tip & Ring).
REN
— Ringer Equivalence Number. An indication of the im-
pedance or loading factor of a telephone bell or ringer circuit.
An REN of 1.0 equals
8.0 k
. The Bell system typically
permits a maximum of 5.0 REN (1.6 k
) on an individual
subscriber line. A minimum REN of 0.2 (40 k
) is required by
the Bell system.
RETURN LOSS
—
Expressed in dB, it is a measure of how
well the SLIC’s AC impedance matches the line’s AC charac-
teristic impedance. With a perfect match, there is no re-
flected signal, and therefore infinite return loss. It is
calculated from:
(ZLine
(ZLine– ZCKT)
RL
20
log
ZCKT)
RING
—
One of the two wires connecting the central office to
a telephone. The name derives from the ring portion of the
plugs used by operators (in older equipment) to make the
connection. Ring is traditionally negative with respect to Tip.
SLIC
— Subscriber Line Interface Circuit. It is the circuitry
within the CO or PBX which connects to the user’s phone
line.
SUBSCRIBER
— The customer at the telephone end of the
line.
SUBSCRIBER LINE
— The system consisting of the user’s
telephone, the interconnecting wires, and the central office
equipment dedicated to that subscriber (also referred to as a
loop).
TIP
— One of the two wires connecting the central office to a
telephone. The name derives from the tip of the plugs used
by operators (in older equipment) to make the connection.
Tip is traditionally positive with respect to Ring.
TRANSHYBRID REJECTION
— The rejection (in dB) of the
reflected signal in the transmit path resulting from a receive
signal applied to the SLIC.
TRANSMIT PATH
— Within the CO or PBX it is the speech
path from the phone line (Tip & Ring) towards the internal
switching system.
TWO WIRE CIRCUIT
— Refers to the two wires connecting
the central office to the subscriber’s telephone. Commonly
referred to as Tip and Ring, the two wires carry both transmit
and receive signals in a differential manner.
TWO–TO–FOUR WIRE CONVERTER
— A circuit which
has four wires (on one side) — two (signal & ground) for the
outgoing signal, and two for the incoming signal. The out-
going signal is sent out differentially on the two wire side (the
other side), and incoming differential signals received on the
two wire side are directed to the four wire side. Additional cir-
cuit within cancels the reflected outgoing signal to keep it
separate from the incoming signal.
VOICEBAND
— That portion of the audio frequency range
used for transmission across the telephone system. Typi-
cally, it is 300 to 3400 Hz.
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