MH88620BR
340Ω between Z1 and Z2. The design uses a 0.1
times impedance amplifier so the 340Ω actually adds
34Ω of additional impedance to the 850Ω (16 + 34 +
850 = 900). For complex impedance setting, a
capacitor and/or resistor can be connected between
Z1 and Z2. For example, if Return Loss is to be
maximised for a Zin of 900 +2.2µF, a 0.22µF cap can
be connected between Z1 and Z2.
Preliminary Information
DTMF
The DTMF tones are transmitted and received at the
4-wire port.
High voltage Capability
Inherent in the thick-film process is the ability of the
substrate to handle high voltage. The standard Mitel
thick-film process provides dielectric strengths of
greater than 1000 VAC or 1500 VDC. The thick-film
process allows easy integration of surface mount
components such as the high voltage bipolar power
transistor line drivers. This allows for simpler, less
elaborate and less expensive protection circuitry
required to handle high voltage transcients and fault
conditions caused by lightning, induced voltages and
power line crossings.
Network Balance
Transhybrid loss is maximised when the line
termination impedance and SLIC network balance
are matched. The MH88620BR’s network balance
impedance can be set to Zin, or to a user selectable
value. Thus, the network balance impedance can be
set to any Brazilian or other international
requirement.
An external Network Balance
impedance is selected which 0.1 times the
impedance between N1 and AGND. N2 to GND
balances to 900Ω.
On-Hook Transmission
The MH88620BR provides for on-hook transmission
which supports features such as Automatic number
identification (ANI). The ANI information is a FSK or
DTMF signal originating from and sent by the C.O.
during the off period of the ringing voltage being sent
to the subscriber’s set. The signal is present during
the off period between the first and second ring. The
subscriber’s set decodes the identification signal and
displays the calling party’s number.
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.
Dial pulses can be detected by monitoring the
interruption rate at the SHK pin. These dial pulses
would be debounced by the system software.
Loop Length
The MH88620BR can accommodate loop lengths of
up to 2000 ohms minimum (including the subscriber
equipment). This corresponds to approximately
8kmusing #26 AWG twisted pair or 15km using #24
AWG twisted pair.
Ring Trip Detection
The interface permits detection of an Off-Hook
condition during 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.
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 40 mA RMS at
60 Hz.
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MITEL [ MITEL NETWORKS CORPORATION ]
