MH89760B
Preliminary Information
detailed transformer specification is presented in the
applications section of this data sheet.
of the receiver circuit is set at approximately 1.5V.
There is no equalization of the received signal. The
receiver circuit is designed to accurately decode a
signal attenuated by a maximum of 3 dB from the
digital crossconnect point. The MH89760B is not
designed to directly accept a signal from the last
network repeater. Interface to the public network
generally requires a Channel Service Unit (CSU).
The receiver decodes the bipolar signal into a split
phase unipolar return to zero format. The two
resulting unipolar signals are used for bipolar
violation detection within the device and are also
output at RxA and RxB. The input jitter tolerance of
the MH89760B is shown in Figure 7.
To complete the interfaces to the transmit line, a pre-
equalizer and line impedance matching network is
required. The pulse output at the transformer
secondary must be pre-equalized to drive different
lengths of cable. Mitel‘s MH89761 T1 Equalizer is
configurable to provide pre-emphasis for 0-150, 150-
450 and 450-655 foot lengths of 22 AWG
transmission line. A separate 6dB pad is also
provided on the MH89761 for use in implementing
external looparound. Both circuits have input and
output impedance of 100Ω. Figure 6 shows how the
equalizer is connected in a typical application. (Refer
to the MH89761 data sheet for more details.)
Elastic Buffer
Line Receiver
The MH89760B has a two frame elastic buffer which
absorbs jitter in the received DS1 signal. The buffer
is also used in the rate conversion between the
1.544 Mbit/s DS1 rate and the 2.048 Mbit/s ST-BUS
data rate.
The bipolar receiver inputs on the device, RxT and
RxR, are intended to be coupled to the line through a
center tapped pulse transformer as shown in Figure
6. The device presents a 400Ω impedance to the
receive transformer to permit matching to 100Ω
twisted pair cable. The signal detect threshold level
20
➀
J
I
10
➁
T
T
E
R
5
A
M
P
L
I
T
U
D
E
1.3
1
(UI)PP
0.5
0.1
120
100
40k
6k
10
1k
10k
100k
JITTER FREQUENCY (Hz)
➀
➁
Typical input jitter tolerance of MH89760B receiver.
Minimum jitter tolerance specified by CCITT in Recommendation I.431.
Figure 7 - Input Jitter Tolerance of the MH89760B
4-68
MITEL [ MITEL NETWORKS CORPORATION ]
