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MH89726/728
MT8972 Loop Extender Circuits Advance Information
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
ISSUE 2
November 1990
Ordering Information MH89726/728 10 Pin SIL Package 0C to 70C
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.
Applications
* * * * Digital subscriber lines Digital PABX line cards and telephone sets High speed, limited distance modem ISDN U - Interface
TXGAIN
TXIN
PreEqualizer
TX Amplifier
TXOUT
Phase Compensator
RXOUT
PreCanceller
RX Amplifier
RXIN RXIN +
VBias
TEST
V+
V-
Figure 1 - Functional Block Diagram
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MH89726/728
Advance Information
TXGAIN TXOUT RXIN + RXIN VVBias V+ TEST RXOUT TXIN
1 2 3 4 5 6 7 8 9 10
Figure 2 - Pin Connections
Pin Description
Pin # 1 Pin Name TXGAIN Description Transmit Gain. To be connected to Pin 2. An increase in gain can be achieved by connecting an external resistor REXT between Pin 1 and Pin 2. The resultant gain is calculated using; A= (R/24) + 2.8, where A=Gain and R= REXT (k). Transmit Output. Connect to the termination network. Negative Receive Signal. Connect to TXOUT, Pin 2. Positive Receive Signal. Connected to line transformer. Negative power supply. Internal Bias Voltage. Connect to GND through 0.33 F for single power supplies. Connect to GND directly for split power supplies. Positive power supply. Test. Used for production testing. Leave unconnected. Receive Output. Connect to LIN (Pin 21) of MT8972. Transmit Input. Connect to LOUT (Pin 1) of MT8972.
2 3 4 5 6 7 8 9 10
TXOUT RXINRXIN+ VVBias V+ TEST RXOUT TXIN
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Advance Information
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 firstorder 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.
MH89726/728
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.
D1, D2 IN5817 Rext Set for different gain requirements MH89726 or MH89728 + 5V 10 22 1 To Power Supplies MT8972 (DNIC) 9 8 7 6 5 4 3 2 1 Rext RLL RLL RL CL MH89726 160 kbit/s 3.9k, 5% 430, 2% 15nF, 5% MH89728 80 kbit/s 3k, 5% 430, 2% 12nF, 5%
D1 21
RL
CL 1.0F 100k
11
D2
Power Supply
Pin 7 (V +)
Pin 6 (VBias)
Pin 5 (V-) - 15V - 30V GND 0.33F
DUAL + 15V GND SINGLE GND GND* SINGLE + 30V GND* *Use 0.33F capacitor to GND
Figure 3 - Typical Connection Diagram for MT8972 and MH89726/728
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MH89726/728
MH89726 (160 kbit/s) CABLE CONFIGURATION DNIC to DNIC DNIC with LEC to DNIC with LEC 24 AWG (8.0 dB/km at 120 kHz) 0.0 to 4.1 km 0.65 to 5.1 km
Advance Information
26 AWG (11.5 dB/km at 120 kHz) 0.0 to 3.0 km 0.5 to 3.6 km
Table 1 - Typical Transmission Performance at 160 kbit/s
MH89728 (80 kbit/s) CABLE CONFIGURATION DNIC to DNIC DNIC with LEC to DNIC and LEC 24 AWG (6.9 dB/km at 60 kHz (Note 1) 0.0 to 5.2 km 0.9 to 6.5 km 26 AWG (10.0 dB/km at 60 kHz) 0.0 to 3.4 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.
CB MT8972 1 LOUT RA +5V
80 kbit/s RA = 390 CA = 22nF CB = 3.3nF 160 kbit/s RA = 390 CA = 22nF CB = 1.5nF
CA
2:1 D1 LIN 21 D2 LEIN LOOP EXTENDER and Network Termination 1.0F LEOUT1 Twisted Pair Copper 24-26 Gauge
LEOUT2 0.33F 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 the Loop Extender
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Advance Information
Recommended Operating Conditions
Characteristics 1 2 3 + 15 V Supply - 15 V Supply Standby Current Sym VDD VSS IS Min 13.5 -16.5 Typ 15.0 -15.0 3.0 Max 16.5 -13.5 Units V V mA
MH89726/728
Test Conditions Note 1 Note 2
Note 1: A single voltage supply of +30V10% can be used on V DD with VBias grounded through a 0.33 F capacitor and V SS grounded. Note 2: A single voltage supply of -30V10% can be used on VSS with VBias grounded through a 0.33 F capacitor and V DD grounded.
A.C. Electrical Characteristics
Characteristics 1 2 3 4 5 6 Active Current TX Gain TX Phase Angle RX Gain RX Phase Angle Line Power Sym IA ATX TX ARX RX Min Typ 7.0 9.0 -170.0 0.0 12.0 10.0 Max Units mA dB dB dBm Test Conditions @ 60 kHz for 80 kbit/s @120 kHz for 160 kbit/s @ 60 kHz for 80 kbit/s @120 kHz for160 kbit/s @ 60 kHz for 80 kbit/s @120 kHz for 160 kbit/s @ 60 kHz for 80 kbit/s @120 kHz for160 kbit/s @ 60 kHz for 80 kbit/s @120 kHz for160 kbit/s With 2:1 transformer
9-111
MH89726/728
Advance Information
1.020 - 0.980 (2.590 - 2.490)
0.140 (0.356)
0.405 - 0.345 (1.029 -0.876)
0.190 - 0.180 (0.483 - 0.457) 0.01 (0.025) 0.105 - 0.095 (0.241 - 0.267) 0.025 - 0.015 (0.064 - 0.038)
All dimensions are in inches (centimeters).
Figure 4 - Mechanical Data
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