CMX868E2 View Datasheet(PDF) - MX-COM Inc
Part Name
Description
MFG CO.
'CMX868E2' PDF : 43 Pages View PDF
Low Power V.22bis Modem
13
CMX868 Advance Information
4.7 Rx Modem Filtering and Demodulation
When the receive part of the CMX868 is operating as a modem, the received signal is fed to a bandpass filter
to attenuate unwanted signals and to provide fixed compromise line equalization for 600, 1200 and 2400bps
FSK, DPSK and QAM modes. The characteristics of the bandpass filter and equalizer are determined by the
chosen receive modem type and frequency band. The line equalizer may be enabled or disabled by bit 10 of
the General Control Register and compensates for one quarter of the relative amplitude and delay distortion
of ETS Test Line 1.
The responses of these filters, including the line equalizer and the effect of external components used in
Figure 4 and Figure 5, are shown in Figure 10, Figure 11, Figure 12, and Figure 13:
10
0
-10
-20
-30
dB
-40
-50
-60
0
0.5
1
1.5
2
2.5
3
3.5
4
kHz
10
0
-10
-20
dB -30
-40
-50
-60
0
0.5
1
1.5
2
2.5
3
3.5
4
kHz
Figure 10: QAM/DPSK Rx Filters
Figure 11: V.21 Rx Filters
10
0
-10
-20
-30
dB
-40
-50
-60
0
0.5
1
1.5
2
2.5
3
3.5
4
kHz
Figure 12: Bell 103 Rx Filters
10
0
-10
-20
dB -30
-40
-50
-60
0
0.5
1
1.5
2
2.5
3
3.5
4
kHz
Figure 13: Bell 202 / V.23 Rx Filters
The signal level at the output of the Receive Modem Filter and Equalizer is measured in the Modem Energy
Detector block, compared to a threshold value, and the result controls bit 10 of the Status Register.
The output of the Receive Modem Filter and Equalizer is also fed to the FSK or QAM/DPSK demodulator
depending on the selected modem type.
¤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
All trademarks and service marks are held by their respective companies.
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