Preliminary Information
MT9075A
Tx
Manufacturer
Filtran
Pulse Engineering
For Tx
5721-1
PE-65351
50027
For Rx
5721-2
PE-64934
50026
0.68uF 2.4Ω*
TTIP
TRING
2.4Ω*
1:2
Midcom
* 2.4
Ω
resistors are only
required with 75
Ω
coax
MT9075A
OSEC
02934/A
02935/A
Table 1 - Transformer Manufacturers and Part
Numbers
Timing Source
The MT9075A can use either a clock or crystal,
connecting to pins OSC1 and OSC2, as the
reference timing source.
Figure 6 shows a 20MHz clock oscillator, with 50ppm
tolerance, directly connected to the OSC1 pin of the
MT9075A.
1:1
RTIP
RRING
120Ω/
75Ω
Rx
Figure 4 - Analog Line Interface
The template for the transmitted pulse, as specified in
G703, is shown in Figure 5. The nominal peak voltage
of a mark is 3 volts for 120
Ω
twisted pair applications
and 2.37 volts for 75
Ω
coax applications. The ratio of
the amplitude of the transmit pulses generated by TTP
and TRING is between 0.95 and 1.05.
+
5V
MT9075A
OSC1
20MHz
OUT
Vdd
GND
.1µF
Percentage of
Nominal Peak
120
110
100
90
80
269nS
244nS
194nS
OSC2
(
open
)
Figure 6 - Clock Oscillator Circuit
50
10
0
-10
-20
219nS
488nS
Alternatively, a crystal oscillator may be used. A
complete oscillator circuit made up of a crystal,
resistors and capacitors is shown in Figure 7. The
crystal specification is as follows.
Nominal Pulse
Figure 5 - Pulse Template (G.703)
Frequency:
Tolerance:
Oscillation Mode:
Resonance Mode:
Load Capacitance:
Maximum Series Resistance:
Approximate Drive Level:
20MHz
50ppm
Fundamental
Parallel
32pF
35
Ω
1mW
Transformer Recommendation
Table 1 shows a list of recommended transformers
for the MT9075A line interface.
4-137