MH88625
Longitudinal Balance
The longitudinal balance specifies the degree of
common mode rejection in the 2 to 4 wire direction.
Precision laser trimming of internal resistors in the
hybrid ensures good overall longitudinal balance.
The interface circuitry can operate in the presence of
induced longitudinal currents of up to 40mA at 60Hz.
Preliminary Information
Dial pulse can be detected by monitoring the
interruption rate at the SHK pin. These dial pulses
would be debounced by the system’s software.
Ring Trip Detection
The interface permits detection of an Off-Hook
condition during the ringing. If the subscriber set
goes Off-Hook when the ringing signal has been
applied, the DC loop current flow will be detected
within approximately 100msecs and the SHK output
will go low. The ring relay is automatically disabled
by the internal hardware.
Off-Hook and Dial Pulse Detection
The SHK pin goes low when the DC-loop current
exceeds a specified level. The threshold level is
internally set by the bias voltage of the switch-hook
detect circuitry.
MH88625
Z
TRANSMIT GAIN
:
(Tip-Ring to Tx)
5kΩ
-
AV
= – 20 log
0.5 + ----------
RTX
TX
25
5kΩ
RTX
= ---------------------------------
–
AV
GTX1
10kΩ
GTX0
10
Example:
RTX = 38kΩ; AV = +4dB
-
----------
20
Z
10kΩ
-
+
28
27
RTX
– 0.5
Z
RECEIVE GAIN
:
(RX to Tip-Ring)
-
+
Z
10kΩ
RX
26
RRX
5kΩ
-
AV
= – 20log
0.5 + ----------
RRX
5kΩ
RTX
= ---------------------------------
–
AV
10
Example:
RRX = 4.6kΩ; AV = -4dB
-
----------
20
GRX1
30
GRX0
10kΩ
29
– 0.5
Figure 3 - Gain Programming with External Components
2-190
MITEL [ MITEL NETWORKS CORPORATION ]
