Preliminary Information
Pin Description (Continued)
Pin #
16
17
18
19
20
21
22
23
Name
TXB
NC
NC
NC
VDD
E2o
RXB
RXA
Description
MH89793
Transmit B (Input).
A unipolar signal from the framer device used in conjunction with TXA
is used to generate the bipolar output signal.
No Connection.
This pin is used for internal connection.
No Connection.
This pin is used for internal connection.
No Connection.
This pin is used for internal connection.
D.C. Power (Input).
+5V supply.
2048kHz Extraction Clock (Output).
This clock is extracted by the device from the
received signal. It is used internally to clock in data received from RLA and RLB.
Receive B (Output).
This pin is connected to the negative receive pin of the framer and
provides a signal of the same format as RXA.
Receiver A (Output).
The bipolar CEPT signal received by the device at RLA and RLB
input is converted to a unipolar format and output at this pin. This pin is connected to the
positive receive pin of the framer.
Ground (Input).
D.C. power return path.
Loss of Signal (Output).
This pin goes low when 128 contiguous zeros are received on
the RLA and RLB inputs. LOS is reset when 64 ones are received in dual E1 frame periods.
No Connection.
This pin is used for internal connection.
Receive Impedance Select.
This pin is connected to pin 17 RZB to select 75Ω input
impedance. For 120Ω operation this pin is left open circuit.
Receive Impedance Select.
This pin is connected to pin 16 RZA to select 75Ω input
impedance. For 120Ω operation this pin is left open circuit.
24
25
26
27
28
VSS
LOS
NC
RZA
RZB
Functional Description
The MH89793 is an E1 digital trunk interface which
when used with an approved framer will conform to
CCITT recommendation G.703 for PCM30 and I.431
for the ISDN. The functions provided include line
driver and receiver circuitry, inductorless clock
recovery, and loss of signal indication.
Bipolar Line Transmitter
The MH89793 transmitter interfaces to the
transmission line through an internal pulse
transformer which combines the TxA and TxB data
into an AMI line coded signal. This is then passed
through the 6dB pad prior to being applied to the
line.
Bipolar Line Receiver
The MH89793 receiver interfaces to the transmission
line through an internal pulse transformer which
splits the received AMI lines signal into RxA and
RxB. The line impedance is selected by linking
appropriate option pins.
Attenuation of the transmission line shall not exceed
6dB (at 1024kHz) and attenuation characteristics
shall be close to the “square root of f”.
Af (dB) = AF
ref
(dB)*
√f
f
ref
Clock Extractor
The MH89793 contains a clock extraction circuit that
generates the E2o clock from the received data
without the use of external crystals or a tunable
inductor.
The edge of the E2o extracted clock approximately
aligns with the centre of the received data pulse.
Where:
AF - attenuation at frequency f in dB
AF
ref
- attenuation at frequency f
ref
in dB (in kHz)
f
ref
- reference frequency (in this case 1024) kHz
f - frequency in kHz
4-231
MITEL [ MITEL NETWORKS CORPORATION ]
