Low Power V.22 Modem
CMX867A
5.3
Tx Filter and Equaliser
The FSK or DPSK modulator output signal is fed through the Transmit Filter and Equaliser block which
limits the out-of-band signal energy to acceptable limits. In 600 and 1200 bps FSK and DPSK modes this
block includes a fixed compromise line equaliser which is automatically set for the particular modulation
type and frequency band being employed. This fixed compromise line equaliser may be enabled or
disabled by bit 10 of the General Control Register. The amount of Tx equalisation provided compensates
for one quarter of the relative amplitude and delay distortion of ETS Test Line 1 over the frequency band
used.
5.4
DTMF/Tone Generator
In DTMF/Tones mode this block generates DTMF signals or single or dual frequency tones. In DPSK
modem modes it is used to generate the optional 550 or 1800Hz guard tone.
5.5
Tx Level Control and Output Buffer
The outputs (if present) of the Transmit Filter and DTMF/Tone Generator are summed then passed
through the programmable Tx Level Control and Tx Output Buffer to the pins TXA and TXAN. The Tx
Output Buffer has symmetrical outputs to provide sufficient line voltage swing at low values of VDD and to
reduce harmonic distortion of the signal.
© 2008 CML Microsystems Plc
13
D/867A/3
CMLMICRO [ CML MICROCIRCUITS ]
