CMX868 查看數據表（PDF） - MX-COM Inc
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CMX868 Datasheet PDF : 43 Pages
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Low Power V.22bis Modem
8
CMX868 Advance Information
Allowing for 1dB loss in the transformer, then with the Tx Mode Register set for a Tx Level Control gain of 0dB
the nominal transmit line levels will be:
QAM, DPSK and FSK Tx modes (no guard tone)
Single tone transmit mode
DTMF transmit mode
VDD = 3.0V
-10dBm
-10dBm
-6 and -8 dBm
VDD = 5.0V
-5.5dBm
-5.5dBm
-1.5 and -3.5 dBm
For a line impedance of 600:, 0dBm = 775mVRMS. See also Section 6.1.3.
In the receive direction, the signal detection thresholds within the CMX868 are proportional to VDD and are
affected by the Rx Gain Control gain setting in the Rx Mode Register. The signal level into the CMX868 is
affected by the line coupling transformer loss and the values of R11 and R12 of Figure 4.
Assuming 1dB transformer loss, the Rx Gain Control programmed to 0dB and R12 = 100k:, then for correct
operation (see Section 6.1.3) the value of R11 should be equal to 500 / VDD k: i.e. 160k: at 3.0V, falling to
100k: at 5.0V
3.2.2 4-Wire Line Interface
Figure 5 shows an interface for use with a 600: 4-wire line. The line terminations are provided by R10 and
R13, high frequency noise is attenuated by C11 while R11 and R12 set the receive signal level into the
modem.
Transmit and receive line level settings and the value of R11 are as for the 2-wire circuit.
1:1
Rx
4-Wire
Line
Tx
C12
R10
RXAFB
R12
R11
C11
RXA
RXA
C3
R13
VBIAS
TXA
-
+
CMX868
TXA
Figure 5: 4-Wireline Interface Circuit
R10, 13 600: 1 C3
R11
See text
C11
R12
100k:
C12
Resistors r5%, capacitors r20%
See Figure 2
100pF
33nF
Table 5: 4-Wireline Interface Circuit External Components
¤2001 MX-COM, Inc.
www.mxcom.com tel: 800 638 5577 336 744 5050 fax: 336 744 5054
Doc. # 20480205.007
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
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