MITEL MT89761 Datasheet
4-93
Features
• Compatible with th e MH8 9760B
• Transmit equal izer an d 6d B loop ar oun d circ uit
• 6dB pad for easier loopback testing
• Programmable for varying degrees of
equalizat io n
Description
The MH89761 is a programmable transmit equalizer
for use with a T1 line interface, specifically the
MH89760B. The MH89761 contains a three setting
transmit equalizer, and a 6 dB pad for external loop
around. The input and output impedance of the
circuit is 100Ω. The device is fabricated in thick film
hybrid technology and is 2 inches high by 0.5 inches
wide. The MH89761 is designed to drive 22 gauge
twisted pair from the multiplex equipment to the
crossconnect point. Figure 1 shows how the
MH89761 is connected to the transmit side of a T1
interface.
Figure 1 - Connection Diagram
MH89761
TR1
MH89760B
OUTA
OUTB
RxT
RxR
+12V
L2
C2
•
TR2
1:
1:
1:
:0.5
R1
L1
C1
••
•
•
•
•
S1
S2
S3
S4
S5
S6
S7
EIT
EIR
EA
EB
EC
SW
RCLT
RCHT
RCLR
RCHR
Ti
Ri
TxT
TxR
TL
RL
R1 = 150Ω
C1 = .01µF
C2 = .47µF
L1 = 33µH
L2 = 33µH
1:
1:
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Ordering Information -40°C to 85°C
MH89761 20 Pin SIP Hybrid
TL
TL
TI
Ri
RL
RL
TxT
EIT
EA
L1
EB
EC
L2
RCHT
RCLT
TxR
EIR
SW
RCHR
RCLR
Pin Connections
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
ISSUE 4 May 1995
MH89761
T1 Transmit Equalizer
Advance Information
4-94
MH89761 Advance Information
Applications
The MH89761 can be connected to the MH89760B
as illustrated in Figure 1. All pins on the MH89761
not shown connected in Figure 1 should be left open.
The internal circuit of the equalizer is shown in
Figure 2. The MH89761 has two separate circuits; a
6dB pad and an equalizer.
Ti and Ri are inputs to the 6dB pad on the device.
The outputs of the pad are brought out on TL and
RL. The 6dB pad is provided to loopback the
transmit signal back to the receive without altering
the equalizer settings. The 4 pole double throw relay
shown in Figure 1 per m its connection of the output of
the transformer TR1 to either the equalizer or the
fixed 6dB pad. For normal operation and
transmission out to the line, the transformer should
be connected to the equalizer inputs EIT and EIR.
Enabling the relay will switch the connection through
the 6dB pad for loopback diagnostics.
The MH89761 is designed to accept output from the
secondary of the T1 transmit transformer and
condition it for transmission over twisted pair. The
seven switche s (S1 to S7) permit con fi gura tion o f the
equalizer for different line lengths. The pulse
amplitude at the secondary of TR1 is approximately
6V. Passing this signal through the equalizer with
zero line length setting on the switches will result in
attenuation of the pulse by 6dB. This will ensure that
the pulse fits in the tem plate shown in Figure 3 a nd
meets DSX-1
➀
requirements. By switching in
different C and L components, the frequency and
phase response of the equalizer can be altered as
shown in Figures 4 and 5. Note that the circuit
attenuates lower frequencies more than higher
frequencies. Consequently, when a pulse is passed
through the equalizer, lower frequency componen ts in
the signal are a tte nu ated m or e tha n higher fre quency
components. The intention is to compensate for the
attenuation properties of twisted pair cable, which
tends to attenuate higher frequencies more than
lower frequencies. The net result is that a preequalized pulse will meet DSX pulse requirements
after traversing a specific length of cable.
The cable length indicated along withthe equalizer
switch settings in Figure 4 are specific to 22 awg
ABAM cable interfaced to an MH89760B equipped
with a Filtran➁ TFS2573 transformer. Different
equalizer settings may be more appropriate for other
cable and transformer types. Figure 6 shows the
generic switch settings for different levels of
equalization.
➀
Reference: ANSI T1.102 - 1987, Section 2.2
➁
Manufacturer: Filtran Ltd.
(613) 226-1626
Figure 2 - 6dB Pad and Equalizer Pin
Ti
50Ω
6dB Pad
S5
S4
4870pF
2150pF
TxT
EiT
EQUALIZER
TL
Ri
RL
50Ω 50Ω
50Ω 50Ω
100Ω
50Ω
200Ω
50Ω
50Ω 50Ω
100Ω
12Ω
S1
S2
S3
10µH
22µH
50Ω
50Ω
50Ω
200Ω
EiR
TxR
2150pF
S6
S7
4870pF
27Ω
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390Ω
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