Page 1
MH89726/728
MT8972 Loop Extender Circuits
Advance In formation
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
ISSUE 2 November 1990
Ordering Information
MH89726/728 10 Pin SIL Package
0°C to 70°C
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 t ransmit signal ma y be adjusted th rough
the use of a n ex te rn al r e s ist or.
RX
TX
OUT
TX
GAIN
IN
Phase
Compensator
V
Bias
Pre-
Equalizer
Pre-
Canceller
Amplifier
RX
Amplifier
TEST V+V
TX
TX
OUT
RX
-
IN
RX
+
IN
-
Figure 1 - Functional Bloc k Diagram
9-127
Page 2
MH89726/728 Advance Information
TXGAIN
TXOUT
RXIN +
RXIN -
V -
VBias
V +
TEST
RXOUT
TXIN
1
2
3
4
5
6
7
8
9
10
Figure 2 - Pin Conn ectio ns
Pin Description
Pin # Pin Name Description
1TX
2TX
3RX
4RX
GAIN
OUT
ININ+
5V-Negative power supply.
Transmit Gain. To be connected to Pin 2. An increase in gain can be achieved by
connecting an external resistor R
between Pin 1 and Pin 2. The resultant gain is
EXT
calculated using; A= (R/24) + 2.8, where A=Gain and R= R
Transmit Output. Connect to the termination network.
Negative Receive Signal. Connect to TX
OUT
, Pin 2.
Positive Receive Signal. Connected to line transformer.
EXT
(kΩ).
6V
Bias
Internal Bias Voltage. Connect to GND through 0.33 µF for single power supplies.
Connect to GND directly for split power supplies.
7V+Positive power supply.
8TESTTest. Used for production testing. Leave unconnected.
9RX
10 TX
OUT
IN
Receive Output. Connect to LIN (Pin 21) of MT8972.
Transmit Input. Connect to L
(Pin 1) of MT8972.
OUT
9-128
Page 3
Advance Informat ion 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
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
and TX
must be shorted tog e th er, and the defaul t
OUT
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 firstorder pre-cancellation as well as gain and phase
adjustment of the receive signal. The signal is then
output on RX
which is connected to LIN of the
OUT
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, an d cros st alk int erf erenc e.
OUT
, pre-
GAIN
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 u sed if only a single
power supply is available.
Applications
Figure 3 show s a typical connectio n diagram of the
MT8972 and MH 8972 6/72 8. R X
LEC are connected to L
and LIN of the DNIC
OUT
OUT
and T
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
, may be use d
EXT
to increase the ga i n of the tran smi tt er. Without R
TX
GAIN
and TX
are shorted to gether resulting i n
OUT
a transmit power level of +10 dBm.
, RL, and CL comprise the termination network
R
LL
and are used to match the characteristic impedance
of the transmiss ion lin e. T his provides the 4 wi r e t o 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.
XIN
of the
EXT
,
+ 5V
22
MT8972
(DNIC)
11
D1, D2 IN5817
R
Set for different gain requirements
ext
MH89726
or
MH89728
10987654321
R
ext
R
1
D1
21
D2
To Power Supplies
Power
Supply
DUAL
SINGLE
SINGLE
*Use 0.33µF capacitor to GND
Pin 7
(V +)
+ 15V
GND
+ 30V
Pin 6
(V
Bias
GND
GND*
GND*
Pin 5
(V-)
)
- 15V
- 30V
GND
LL
RLC
L
R
R
C
LL
L
L
0.33µF
MH89726
160 kbit/s
3.9kΩ, 5%
430Ω, 2%
15nF, 5%
Figure 3 - Typical Connection Diagram for MT8972 and MH89726/728
1.0µF
100kΩ
MH89728
80 kbit/s
3kΩ, 5%
430Ω, 2%
12nF, 5%
9-129
Page 4
MH89726/728 Advance Information
MH89726 (160 kbit/s)
CONFIGURATION
CABLE
(8.0 dB/km at 120 kHz)
24 AWG
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
Table 1 - Typical Transmission Performance at 160 kbit/s
MH89728 (80 kbit/s)
CONFIGURATION
CABLE
(6.9 dB/km at 60 kHz (Note 1)
24 AWG
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
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.
80 kbit/s RA = 390Ω CA = 22nF CB = 3.3nF
160 kbit/s RA = 390Ω CA = 22nF CB = 1.5nF
CA
MT8972
L
OUT
CB
1
RA
(11.5 dB/km at 120 kHz)
26 AWG
26 AWG
(10.0 dB/km at 60 kHz)
+5V
D1
21
L
IN
D2
LE
NOTES:
-D1, D2 IN5817 (Schottky)
-Solid jumpers used to connect the loop extender
-Dotted jumpers connect MT8972 without loop extender
Figure 4 - Typical Application of th e L oop E xten der
LE
OUT2
IN
LOOP
EXTENDER
and
Network
Termination
LE
OUT1
2:1
0.33µF
1.0µF
Twisted Pair
Copper 24-26
Gauge
9-130
Page 5
Advance Informat ion MH89726/728
Recommended Operating Conditions
Characteristics Sym Min Typ Max Units Test Conditions
1 + 15 V Supply V
2 - 15 V Supply V
3 Standby Current I
Note 1: A single voltage supply of +30V±10% can be used on VDD with V
Note 2: A single voltage supply of -30V±10% can be used on VSS with V
grounded.
grounded.
DD
SS
S
13.5 15.0 16.5 V Note 1
-16.5 -15.0 -13.5 V Note 2
3.0 mA
grounded through a 0.33 µF capacitor and VSS
Bias
grounded through a 0.33 µF capacitor and VDD
Bias
A.C. Electrical Characteristics
Characteristics Sym Min Typ Max Units Test Conditions
1 Active Current I
2TX Gain A
3 TX Phase Angle Φ
4 RX Gain A
5 RX Phase Angle Φ
A
TX
TX
RX
RX
6 Line Power 10.0 dBm With 2:1 transformer
7.0 mA @ 60 kHz for 80 kbit/s
@120 kHz for 160 kbit/s
9.0 dB @ 60 kHz for 80 kbit/s
@120 kHz for160 kbit/s
-170.0 ° @ 60 kHz for 80 kbit/s
@120 kHz for 160 kbit/s
0.0 dB @ 60 kHz for 80 kbit/s
@120 kHz for160 kbit/s
12.0 ° @ 60 kHz for 80 kbit/s
@120 kHz for160 kbit/s
9-131
Page 6
MH89726/728 Advance Information
1.020 - 0.980 (2.590 - 2.490)
0.405 -
0.345
(1.029 -0.876)
0.105 - 0.095
(0.241 - 0.267)
All dimensions are in inches (centimeters).
0.025 - 0.015
(0.064 - 0.038)
Figure 4 - Mechanical Data
0.190 - 0.180
(0.483 - 0.457)
0.140 (0.356)
0.01 (0.025)
9-132
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