13 Jan 2012

CML CMX994 Direct Conversion Receiver

Low power semiconductor company, CML Microcircuits has added a new Direct Conversion Receiver IC or DcRx to its family of RF Integrated Circuits.

This new DcRx integrated circuit is designated the CMX994. It is aimed at the next generation of multi-mode Software Defined Radios, SDR market for wireless data and two-way radio applications. Using the SDR approach, most of the functionality can be contained within the software, making the receiver considerably more flexible and upgradeable. In this way, the design provides the optimum route for on-board integration. It allows a small RF receiver to be realised with a minimum of external components in both zero IF and low IF systems, while also providing for significant levels of functionality within the digital signal processing areas of the receiver.

Until recently, most radios have used the superheterodyne or superhet receiver principle. Here signals on the incoming frequency were converted down to a normally fixed intermediate frequency where it could be filtered and amplified more easily. In some applications a dual conversion superhet may be used. Using a double conversion process reduces issues of image rejection by having a higher first intermediate frequency, while having a low second intermediate frequency stage to provide the required level of filtering without very expensive high frequency filters.

Now enhancements in semiconductor technology have enabled the integration of the direct conversion receiver, allowing it to become the technology of choice for radio receivers in many applications.

A direct conversion receiver mixes the wanted RF signal down to 0Hz in a single quadrature mixing process using a local oscillator, LO tuned to the wanted RF channel frequency.

Selectivity filtering and gain are then undertaken at baseband with practical, low power, analogue and digital circuits. A direct conversion receiver also eliminates the need for an image-reject filter.

Key features of the CMX994 include on-chip VCO for VHF applications, an operating range of 100MHz to 600MHz, precision baseband filtering with selectable bandwidths and the smallest PCB area, typically less than 50% of a dual superhet.

Another important feature is the single ended RF connections meaning no baluns are required. The small size and flexibility of Direct Conversion make it a key element for the next generation of multi-mode software defined radios (SDR) for wireless data and digital two-way radio applications.

The CMX994 is available now, operates at 3.0 - 3.6 V, and comes in a Q4 40-pin VQFN package.

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