CMX867D2 CML Microcircuits, CMX867D2 Datasheet - Page 14

• Manufacturer Part Number: CMX867D2
• Description: Low power V.22 modem
• Manufacturer: CML Microcircuits

Low Power V.22 Modem
1.5.7
When the receive part of the CMX867 is operating as a modem, the received signal is fed to a bandpass
filter to attenuate unwanted signals and to provide fixed compromise line equalisation for 600 and
1200bps FSK and DPSK modes. The characteristics of the bandpass filter and equaliser are determined
by the chosen receive modem type and frequency band. The line equaliser 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 equaliser and the effect of external components used in
Figures 4a and 4b, are shown in Figures 6b-e:
The signal level at the output of the Receive Modem Filter and Equaliser 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 Equaliser is also fed to the FSK or DPSK demodulator
depending on the selected modem type.
dB
dB
2001 Consumer Microcircuits Limited
-10
-20
-30
-40
-50
-60
-10
-20
-30
-40
-50
-60
10
10
0
0
0
0
Rx Modem Filterering and Demodulation
Figure 6b DPSK Rx Filters
Figure 6d Bell 103 Rx Filters
0.5
0.5
1
1
1.5
1.5
kHz
kHz
2
2
2.5
2.5
3
3
3.5
3.5
4
4
14
dB
dB
-10
-20
-30
-40
-50
-60
10
-10
-20
-30
-40
-50
-60
10
0
0
0
0
Figure 6e V.23/Bell 202 Rx Filters
0.5
0.5
Figure 6c V.21 Rx Filters
1
1
1.5
1.5
kHz
kHz
2
2
2.5
2.5
3
3
3.5
3.5
CMX867
D/867/2
4
4