CMX654 Ver la hoja de datos (PDF) - CML Microcircuits
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CMX654 Datasheet PDF : 13 Pages
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V.23 Transmit Modulator
CMX654
1.6 Application Notes
1.6.1 Line Interface
The signals on the telephone line are not suitable for direct connection to the CMX654. A Line Interface circuit
is necessary to:
• Provide high voltage and dc isolation
• Provide the low impedance drive necessary for the line
• Filter the Tx and Rx signals
R3
See below
R6
100kΩ
C5
22µF (±20%)
C7
330pF
Resistors ±1%, capacitors ±10% unless otherwise stated.
Figure 4 Line Interface Circuit
Notes:
•
•
•
The component(s) 'Z' between points B and C should match the line impedance.
Device A1 must be able to drive 'Z' and the line.
R3: The levels in dB (relative to a 775mV rms signal) at 'A', 'B' and 'C' in the line interface circuit are:
'A' = 20Log(VDD/5)
'B' = 'A' + 20Log(100kΩ/R3)
'C' = 'B' - 6
VDD
3.3V
5.0V
'A'
-3.6dB
0dB
R3
100kΩ
150kΩ
'B'
-3.6dB
-3.5dB
'C'
-9.6dB
-9.5dB
© 1998 Consumer Microcircuits Limited
8
D/654/3
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