MT89726 Просмотр технического описания (PDF) - Mitel Networks
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MT89726 Datasheet PDF : 6 Pages
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Advance Information
MH89726/728
Functional Description
The MH89726/728 are 10 pin SIL thick film hybrid
circuits that may be used to extend the loop range
capability of the MT8972 (DNIC). For a detailed
description of the DNIC, refer to the MT8972 data
sheet.
Figure 1 shows a block diagram of the Loop
Extender Circuit (LEC). The LEC takes the line
signal which is transmitted by the DNIC on LOUT, pre-
equalizes, and amplifies it before sending it to the
termination network. The gain of the TX amplifier is
adjustable by using an external resistor between
pins 1 and 2. If no external resistor is added, TXGAIN
and TXOUT must be shorted together, and the default
gain condition exists. This gain results in a transmit
signal power level of +10 dBm.
On the receive side, the LEC receives the differential
line signal from the transformer, and performs first-
order pre-cancellation as well as gain and phase
adjustment of the receive signal. The signal is then
output on RXOUT which is connected to LIN of the
MT8972.
Tables 1 and 2 show typical results obtained by
using the LEC with the MT8972. Actual distance
achieved may vary depending on the characteristics
of the transmission cable being used. Most
important factors include cable attenuation (dB/km),
bridged taps, and crosstalk interference.
The LEC is powered typically from ±15 Volts if dual
power supplies are available. Alternately 0 to +30
Volts, or -30 to 0 Volts can be used if only a single
power supply is available.
Applications
Figure 3 shows a typical connection diagram of the
MT8972 and MH89726/728. RXOUT and TXIN of the
LEC are connected to LOUT and LIN of the DNIC
respectively. Pins 5, 6 and 7 are the power supply
pins, with the voltages being supplied as indicated in
the table . An external resistor, REXT, may be used
to increase the gain of the transmitter. Without REXT,
TXGAIN and TXOUT are shorted together resulting in
a transmit power level of +10 dBm.
RLL, RL, and CL comprise the termination network
and are used to match the characteristic impedance
of the transmission line. This provides the 4 wire to 2
wire hybrid conversion necessary for twisted pair
transmission.
Figure 4 shows a typical application of the LEC. On
short loops, jumpers (or switches) could be used to
remove the LEC from the circuit. For longer loops,
the jumpers could be changed to include the LEC in
the signal path.
+ 5V
MH89726
or
MH89728
10 9 8 7 6 5 4 3 2 1
22
1
MT8972
(DNIC)
D1
To Power Supplies
Rext
RLL
RL CL
21
11
D2
Power
Supply
Pin 7
(V +)
Pin 6
(VBias)
DUAL + 15V
SINGLE GND
SINGLE + 30V
GND
GND*
GND*
*Use 0.33µF capacitor to GND
Pin 5
(V-)
- 15V
- 30V
GND
D1, D2 IN5817
Rext Set for different gain requirements
MH89726
160 kbit/s
MH89728
80 kbit/s
RLL 3.9kΩ, 5%
RL 430Ω, 2%
CL 15nF, 5%
3kΩ, 5%
430Ω, 2%
12nF, 5%
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
0.33µF
1.0µF
100kΩ
Figure 3 - Typical Connection Diagram for MT8972 and MH89726/728
9-129
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