Telephone Signalling Transceiver / Least Cost Router
CMX860
1.5.2 FSK Modulator
Serial data from the USART is fed to the FSK modulator. One of two frequencies is generated according
to the current transmit data bit.
1.5.3 Tx Filter and Equaliser
The FSK modulator output signal is fed through the Transmit Filter and Equaliser block which limits the
out-of-band signal energy to acceptable limits. When transmitting 1200bps FSK, this block includes a
fixed compromise line equaliser which 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.
1.5.4 DTMF/Tones Generator
In DTMF/Tones mode this block generates DTMF signals or single or dual frequency tones.
1.5.5 Tx Level Control and Output Drivers
The CMX860 generated signal (if present) from the FSK/DTMF/Tones Generator is passed through the
programmable Tx Level Control before being passed to the switched paths controlled by the Analogue
Signal Path Register. The Tx Output Drivers have symmetrical outputs to provide sufficient line voltage
swing at low values of AVDD and to reduce harmonic distortion of the signal. The Drivers can also
transmit the signal from the other port (e.g. Phone Input to Line Driver) or can be independently set to
Bias or Powersaved – see Analogue Signal Path Register.
ã 2002 Consumer Microcircuits Limited
14
D/860/5
CMLMICRO [ CML MICROCIRCUITS ]
