CMX654D4 データシートの表示（PDF） - MX-COM Inc
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CMX654D4 Datasheet PDF : 12 Pages
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V.23 Transmit Modulator
8
CMX654 PRELIMINARY INFORMATION
5 Application Notes
5.1 Line Interface
The signals on the telephone line are not suitable for direct connection to the CMX654. A Line Interface
circuit is necessary to:
x Provide high voltage and DC isolation
x Provide the low impedance drive necessary for the line
x Filter the Tx and Rx signals
C
C5+
LINE
1:1
0V
B
POSSIBLE
Z RECEIVE - HYBRID
CIRCUITRY
C7
R6
A1
Figure 5: Line Interface Circuit
A
R3
TXOUT
VBIAS
R3
Note 3
R6
100k:
C5
22PF (r20%)
C7
330pF
Resistors r1%, capacitors r10% unless otherwise stated.
Notes:
1. The component(s) 'Z' between points B and C should match the line impedance.
2. Device A1 must be able to drive 'Z' and the line.
3. R3: The levels in dB (relative to a 775mVRMS signal) at 'A', 'B' and 'C' in the line interface circuit are:
‘A' = 20Log(VDD/5)
'B' = 'A' + 20Log(100k:/R3)
'C' = 'B' - 6
VDD
3.3V
5.0V
'A'
-3.6dB
0dB
R3
100k:
150k:
'B'
-3.6dB
-3.5dB
'C'
-9.6dB
-9.5dB
¤1998 MX-COM, Inc.
www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054
Doc. # 20480186.001
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All Trademarks and Service marks are held by their respective companies.
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