CMX867D2 CML Microcircuits, CMX867D2 Datasheet - Page 8

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

Low Power V.22 Modem
The transmit line signal level is determined by the voltage swing between the TXA and TXAN pins, less
6dB due to the line termination resistor R13, and less the loss in the line coupling transformer.
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:
For a line impedance of 600 , 0dBm = 775mVrms. See also section 1.7.1.3
In the receive direction, the signal detection thresholds within the CMX867 are proportional to V
are affected by the Rx Gain Control gain setting in the Rx Mode Register. The signal level into the
CMX867 is affected by the line coupling transformer loss and the values of R11 and R12 of Figure 4a.
Assuming 1dB transformer loss, the Rx Gain Control programmed to 0dB and R12 = 100k , then for
correct operation (see section 1.7.1.3) the value of R11 should be equal to 500 / V
3.0V, falling to 100k
4-Wire Line Interface
Figure 4b shows an interface for use with a 600
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.
2001 Consumer Microcircuits Limited
DPSK and FSK Tx modes (no guard tone)
Single tone transmit mode
DTMF transmit mode
R10, 13
R11
R12
at 5.0V
600
See text
100k
Figure 4b 4-Wire Line Interface Circuit
Resistors 5%, capacitors 20%
4-wire line. The line terminations are provided by R10
8
C3
C11
C12
-6 and -8 dBm
V
DD
-10dBm
-10dBm
= 3.0V
See Figure 2
100pF
33nF
DD
-1.5 and -3.5 dBm
k
V
-5.5dBm
-5.5dBm
DD
i.e. 160k
= 5.0V
DD
CMX867
and
D/867/2
at