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Product category: Communications ICs (Wired)
News Release from: CML Microcircuits | Subject: CMX981
Edited by the Electronicstalk Editorial Team on 19 March 2004

Enhanced baseband codec
for modern digital radio

The CMX981 is an extremely-low-power advanced digital-radio baseband processor, combined on-chip with a voice codec/processor and an audio PA

The CMX981 interfaces the analogue and digital sections of a digital radio system and performs many of the radio's critical DSP-intensive functions. The overall functionality of this product within a digital radio application relieves the host processor of a significant amount of processing, therefore allowing for an overall reduction in power consumption.

Additionally, less powerful DSPs can be considered.

The CMX981 supports digital fixed, portable and mobile Tetra, Apco 25, Tetrapol and the Japanese RCR and ARIB system applications, and is sufficiently flexible for use in other demanding digital radio systems.

With this latest two-way radio product from CML, integrated functions, smaller processor requirement, less PCB area and components and minimised power consumption all lead to much reduced design times and much lower project and operational costs.

In its transmit path the CMX981 offers all the functions required to convert digital 'symbol' data into suitably filtered analogue I and Q signals for external up-conversion and transmission.

Also available to the Tx function is digital control of output amplitudes and offsets; all in-path digital filters are fully programmable.

The product's default coefficients provide the root raised cosine (RRC) path responses required for Tetra operation; flexible clock and sample rates allow many different voice codec and signal codec rates to be accommodated.

The CMX981 receive path accepts differential analogue baseband I/Q signals, samples them and performs digital channel select filtering to simplify host processing and data extraction.

Internal digital offset correction and the digital filters are fully programmable.

Auxiliary DAC and ADC functions are included for the control and measurement of the radio and other operations.

These functions could be used for AFC, AGC, RSSI, forward and reverse power monitoring and control or as part of the control system for a Cartesian loop.

The on-chip voice codec can be configured to apply a digital voice filter as required, including the operation to the G.712 specification.

Its encode path accepts a differential analogue audio input signal, converts it to digital form and applies digital voice filtering to produce a processed digital stream.

The decode path accepts a digital stream written to the serial interface, applies digital voice filtering, converts the result to an analogue signal and presents the signal at the speaker or single-ended earphone analogue driver outputs.

The Rx path also includes a side-tone function and an audio-tone generator.

CML is working with both Fjord-e-design and Etherstack, respectively, in the availability of protocol stacks for the Tetra and Apco 25 environments.

With a very low operating power requirement in the 2.25 to 2.75V range, the CMX981 is available in a compact 64-lead VQFN package.

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