9-127

Features

Operates from single or dual power supply

MH89726 extends transmission performance
for the MT8972 (DNIC) at 160kbit/s line rate

MH89728 extends transmission performance
for the MT8972 (DNIC) at 80kbit/s line rate

MH89726 and MH89728 are pin for pin
compatible with each other

Compact SIL package

Over 6km loop range on 24 AWG

Applications

Digital subscriber lines

Digital PABX line cards and telephone sets

High speed, limited distance modem

ISDN U - Interface

Description

The MH89728 and MH89726 are thick film hybrid
devices which may be used to extend the operating
range of the MT8972 (DNIC). The hybrids combine
signal equalization and amplification for the receive
and transmit paths on each device.

The small size of these hybrids makes them suitable
for line card or terminal use with the MT8972. The
gain of the transmit signal may be adjusted through
the use of an external resistor.

Figure 1 - Functional Block Diagram

OUT

Bias

TEST

V+

V-

OUT

GAIN

Pre-

Equalizer

Phase

Compensator

Pre-

Canceller

Amplifier

Ordering Information

MH89726/728 10 Pin SIL Package

0°C to 70°C

ISSUE 2

November 1990

MH89726/728

MT8972 Loop Extender Circuits

Advance Information

9-128

MH89726/728

Advance Information

Figure 2 - Pin Connections

Pin Description

Pin #

Pin Name

Description

GAIN

Transmit Gain. To be connected to Pin 2. An increase in gain can be achieved by
connecting an external resistor R

EXT

between Pin 1 and Pin 2. The resultant gain is

calculated using; A= (R/24) + 2.8, where A=Gain and R= R

EXT

OUT

Transmit Output. Connect to the termination network.

IN-

Negative Receive Signal. Connect to TX

OUT

, Pin 2.

IN+

Positive Receive Signal. Connected to line transformer.

V-

Negative power supply.

Bias

Internal Bias Voltage. Connect to GND through 0.33 µF for single power supplies.
Connect to GND directly for split power supplies.

V+

Positive power supply.

TEST

Test. Used for production testing. Leave unconnected.

OUT

Receive Output. Connect to L

(Pin 21) of MT8972.

Transmit Input. Connect to L

OUT

(Pin 1) of MT8972.

TXGAIN

TXOUT

RXIN +

RXIN -

V -

VBias

V +

TEST

RXOUT

TXIN

9-129

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 L

OUT

, 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, TX

GAIN

and TX

OUT

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 RX

OUT

which is connected to L

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. RX

OUT

and T

XIN

of the

LEC are connected to L

OUT

and L

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, R

EXT

, may be used

to increase the gain of the transmitter. Without R

EXT

GAIN

and TX

OUT

are shorted together resulting in

a transmit power level of +10 dBm.

, R

, and C

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.

Figure 3 - Typical Connection Diagram for MT8972 and MH89726/728

MT8972

(DNIC)

MH89726

MH89728

+ 5V

To Power Supplies

ext

0.33

1.0

100k

D1, D2 IN5817
R

ext

Set for different gain requirements

MH89726
160 kbit/s

MH89728
80 kbit/s

3.9k

, 5%

430

, 2%

15nF, 5%

, 5%

430

, 2%

12nF, 5%

Power
Supply

DUAL
SINGLE
SINGLE

Pin 7
(V +)

+ 15V
GND
+ 30V

Pin 6
(V

Bias

)

GND
GND*
GND*

Pin 5
(V-)

- 15V
- 30V
GND

*Use 0.33

F capacitor to GND

9-130

MH89726/728

Advance Information

Table 1 - Typical Transmission Performance at 160 kbit/s

Table 2 - Typical Transmission Performance at 80 kbit/s

Note 1: The attenuation of the cable as specified by Bell System Technical Reference PUB 62411.

Figure 4 - Typical Application of the Loop Extender

MH89726 (160 kbit/s)

CABLE

CONFIGURATION

24 AWG

(8.0 dB/km at 120 kHz)

26 AWG

(11.5 dB/km at 120 kHz)

DNIC to DNIC

0.0 to 4.1 km

0.0 to 3.0 km

DNIC with LEC to DNIC with LEC

0.65 to 5.1 km

0.5 to 3.6 km

MH89728 (80 kbit/s)

CABLE

CONFIGURATION

24 AWG

(6.9 dB/km at 60 kHz (Note 1)

26 AWG

(10.0 dB/km at 60 kHz)

DNIC to DNIC

0.0 to 5.2 km

0.0 to 3.4 km

DNIC with LEC to DNIC and LEC

0.9 to 6.5 km

0.65 to 4.1 km

OUT

+5V

OUT1

LOOP

EXTENDER

and

Network

Termination

MT8972

OUT2

0.33

1.0

2:1

Twisted Pair
Copper 24-26
Gauge

NOTES:
-D1, D2 IN5817 (Schottky)
-Solid jumpers used to connect the loop extender
-Dotted jumpers connect MT8972 without loop extender

80 kbit/s RA = 390

CA = 22nF CB = 3.3nF

160 kbit/s RA = 390

CA = 22nF CB = 1.5nF

9-131

Advance Information

MH89726/728

Note 1: A single voltage supply of +30V±10% can be used on VDD with VBias grounded through a 0.33 µF capacitor and VSS

grounded.

Note 2: A single voltage supply of -30V±10% can be used on VSS with VBias grounded through a 0.33 µF capacitor and VDD

grounded.

Recommended Operating Conditions

Characteristics

Sym

Min

Typ

Max

Units

Test Conditions

+ 15 V Supply

13.5

15.0

16.5

Note 1

- 15 V Supply

-16.5

-15.0

-13.5

Note 2

Standby Current

3.0

A.C. Electrical Characteristics

Characteristics

Sym

Min

Typ

Max

Units

Test Conditions

Active Current

7.0

@ 60 kHz for 80 kbit/s
@120 kHz for 160 kbit/s

TX Gain

9.0

@ 60 kHz for 80 kbit/s
@120 kHz for160 kbit/s

TX Phase Angle

-170.0

@ 60 kHz for 80 kbit/s
@120 kHz for 160 kbit/s

RX Gain

0.0

@ 60 kHz for 80 kbit/s
@120 kHz for160 kbit/s

RX Phase Angle

12.0

@ 60 kHz for 80 kbit/s
@120 kHz for160 kbit/s

Line Power

10.0

dBm

With 2:1 transformer

Ð­Ð»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: MH89728

ÐÐ»ÐµÐºÑ‚Ñ€Ð¾Ð½Ð½Ñ‹Ð¹ ÐºÐ¾Ð¼Ð¿Ð¾Ð½ÐµÐ½Ñ‚: MH89728