CMX624P4 CMLMICRO [CML Microcircuits], CMX624P4 Datasheet - Page 16

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CMX624P4

Manufacturer Part Number
CMX624P4
Description
V.23 / Bell 202 Modem
Manufacturer
CMLMICRO [CML Microcircuits]
Datasheet

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Part Number
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Part Number:
CMX624P4
Manufacturer:
CML
Quantity:
20 000
V23 / Bell 202 Modem
In the transmit direction, the level on the 4-wire line is determined by the level at the TOP pin, the gain
of the Output Buffer Amplifier, a loss of nominally 6dB due to the line termination resistor R15, and the loss
in the transformer.
The TOP pin signal level is proportional to V
control bit (bit 2) of the FSK Mode Register.
Assuming that the Tx o/p level control bit is set to ‘1’ (giving a FSK signal level of -3dB wrt 775mVrms at
the TOP pin when V
For example, to generate a nominal Tx FSK line level of -9dBm, R13 should be 180k
falling to 120k
2-Wire Line Interface
Figure 8b shows an interface circuit suitable for connection to a 600
how a relay may be driven from the RLYDRV pin. Note that when the CMX624 is powered from less than
5.0V, buffer circuitry will be required to drive a 5V relay.
This circuit includes a 2-wire to 4-wire hybrid circuit, formed by R11, R15, R16, R17, C13 and the
impedance of the line itself, which ensures that the modem receive input and transmit output paths are
both coupled efficiently to the line, while minimising coupling from the modem’s transmit signal into the
receive input.
The values of R11 and R13 should be calculated in the same way as for the 4-wire interface circuit of
Figure 8a.
 2003 CML Microsystems Plc
Tx FSK 4-wire line level = -(3 +6 +1) + 20 x LOG
R11
R12
R13
R14
at 3.3V.
DD
Note ac and dc loads and line protection not shown for clarity.
See text
100k
See text
100k
= 5.0V) and that there is 1dB loss in the transformer, then:
Figure 8b 2-Wire Line Interface Circuit
Resistors 1%, capacitors 20%
DD
R15
R16
R17
10
and is also affected by the setting of the Tx o/p level
16
(2 x R14 / R13) + 20 x LOG
600
120k
100k
2-wire line. The circuit also shows
10
(V
C11
C12
C13
C14
DD
/ 5.0) dBm
when V
220pF
330pF
10nF
100nF
DD
CMX624
= 5.0V,
D/624/7

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