MH88634B
Network Balance Impedance
The
MH88634BV-2/BT-2’s
Impedance is fixed at 600Ω.
Network
Balance
Advance Information
Ringing Voltage Detect Output (RV)
The RV output provides a logic 0 when ringing
voltage is detected across Tip and Ring. This
detector includes a filter which ensures that the
output toggles at the ringing cadence and not at the
ringing frequency. Typically this output switches to a
logic 0 after 50ms of applied ringing voltage and
remains at a logic 0 for 50ms after ringing voltage is
removed.
The threshold is different on the two variants. The
900R part has been designed to meet the ring
sensitivity requirements of TR57, 30 not detecting
ringin below 35Vrms.
Forward Loop and Reverse Loop Detect Outputs
(FL & RL)
The FL output provides a logic 0 when either forward
loop battery or forward loop current is detected, that
is the Ring pin voltage is more negative than the Tip
pin voltage.
The RL output provides a logic 0 when either reverse
loop battery or reverse loop current is detected, that
is the Tip pin voltage is more negative than the Ring
pin voltage.
Switch Hook (SHK)
The SHK output is active if either forward loop or
reverse loop current is detected, or if forward or
reverse battery voltage is detected.
The MH88634BV-4 Network Balance Impedance is
fixed at 900R.
2-4 Wire Conversion
The device converts the balanced 2-Wire input,
presented by the line at Tip and Ring, to a ground
referenced signal at TX. This circuit operates with or
without loop current; signal reception with no loop
current is required for on-hook reception enabling the
detection of Caller Line Identification (CLI) signals.
Conversely the device converts the ground
referenced signal input at RX, to a balanced 2-Wire
signal across Tip and Ring.
The 4-Wire side (TX and RX) can be interfaced to a
filter/codec, such as the Mitel MT896X, for use in
digital voice switched systems
During full duplex transmission, the signal at Tip and
Ring consists of both the signal from the device to
the line and the signal from the line to the device.
The signal input at RX, being sent to the line, must
not appear at the output TX. In order to prevent this,
the device has an internal cancellation circuit. The
measure of attenuation is Transhybrid Loss (THL).
Transmit and Receive Gain
The Transmit Gain of the device is the gain from the
balanced signal across Tip and Ring to the ground
referenced signal at TX. It is set at 0dB.
The Receive Gain of the device is the gain from the
ground referenced signal at RX to the balanced
signal across Tip and Ring. It is set at -2dB.
The MH88634 accepts a control signal from the
system controller at the Loop Relay Control input
(LRC). This energises the relay drive output Loop
Relay Drive (LRD). The output is active low and has
an internal clamp diode to VRLY.
The intended use of this relay driver is to add and
remove the Line Termination from across Tip and
Ring, as shown in Figure 3.
If this Control input and the Supervisory Features are
used as indicated in Figure 3, Loop-Start Signalling
can be implemented.
Control Input
Supervision Features
Line Status Detection Outputs
The MH88634 supervisory circuitry provides the
signalling status outputs which are monitored by the
system controller. The supervisory circuitry is
capable of detecting: Ringing Voltage; Forward and
Reverse loop battery; Forward and Reverse loop
current; and Switch Hook.
Mechanical Data
See Figure 9
specification.
for
details
of
the
mechanical
2-268
MITEL [ MITEL NETWORKS CORPORATION ]
