Preliminary Information
MH88632B
User defined Input Impedances can be used to
satisfy most national requirements. See Table 1.
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.
All connections should be kept as short as possible.
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).
Network Balance Impedance
The MH88632B’s Network Balance Impedance can
be selected to mirror the Input Impedance, to be
AT&T compromise or set to a user defined value.
Thus, the Network Balance Impedance can comply
with most national requirements.
Programmable Transmit and Receive Gain
With NS at logic 0, the Network Balance Impedance
is selected to mirror the Input Impedance of the
device. No connection should be made to NATT, N1
and N2.
The Transmit Gain (GTX) of the MH88632B is the
gain from the balanced signal across Tip and Ring to
the ground referenced signal at TX.
It is
programmed by making a connection to GTX1. A
direct connection from GTX1 to GTX0 selects a gain
of 0dB. A direct connection from GTX1 to AGND
To select a Network Balance Impedance equal to
AT&T Compromise (i.e. 350Ω+(1kΩ//210nF) ), NS
should be set to a logic 1 and a direct connection
made between NATT and N1. No connection should
be made to N2.
selects a gain of +6dB.
Other gains can be
programmed by connecting a resistor (R ) between
TX
GTX1 and AGND. The value of resistor is selected
using the following formulae.
To set a user defined Network Balance Impedance
NS is set to a logic 1. An impedance network which
is 10 times the required Network Balance Impedance
must be placed between N1 and AGND. Another
impedance network must be placed between N1 and
N2 which is 10 times the selected input impedance
of the device.
R
=
5000
TX
(-GTX/20)
10
- 0.5
GTX = - 20 log(0.5+5000)
R
TX
The Receive Gain (GRX) of the MH88632B is the
gain from the ground referenced signal at RX to the
For example, to implement a Network Balance
Impedance of 220Ω+(820Ω//115nF), an impedance
network of 2200Ω+(8200Ω//11.5nF) must be
connected between N1 and AGND. An impedance
network equal to 10 times the selected Input
Impedance must be connected between N1 and N2.
See Table 2.
balanced signal across Tip and Ring.
It is
programmed by making a connection to GRX1. A
direct connection from GRX1 to GRX0 selects a gain
of 0dB. A direct connection from GRX1 to AGND
selects a gain of +6dB.
Other gains can be
programmed by connecting a resistor (R ) between
RX
GRX1 and AGND. The value of resistor is selected
using the following formulae.
All connections should be kept as short as possible.
R
=
5000
(-GRX/20)
RX
2-4 Wire Conversion
10
- 0.5
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 signals.
GRX = -20 log(0.5+5000)
R
RX
For the correct programming of Transmit and
Receive Gains the selected Input Impedance must
match the specified telephone line characteristic
impedance.
Conversely the device converts the ground
referenced signal input at RX, to a balanced 2-Wire
signal across Tip and Ring.
2-243
MITEL [ MITEL NETWORKS CORPORATION ]
