Kaben Wireless Silicon

Software defined radios promise to provide one transceiver capable of handling multiple wireless standards, ranging from Bluetooth, to GSM, to WiMax. Although most of the functionality of modulation / demodulation, synchronization, channel equalization, etc. can be performed in the software back-end, certain functions such as up / down-conversion, amplification and channel filtering must be performed in an RF front-end. With at least a minimal RF front-end being required, performance for each of the standards to be supported can be enhanced by designing-in appropriate reconfigurability.

There are two critical RF circuits necessary for the realization of a reconfigurable, integrated RF front-end: a frequency tunable, bandwidth selectable, on-chip IF filter (to minimize interference); and a wide band frequency synthesizer having low phase-noise and spur level (to minimize its effect on the signal EVM - Error Vector Magnitude). In addition, a digital-to-IF converter replacing the traditional DAC, can simplify the transmitter architecture by removing the need for complex (I and Q) analog up-converters and their amplitude and phase balance control circuits.

The Kaben transceiver front-end, based on three of its key technologies; the Sampling IF fliter (SIF), the Synthesizer, and the Digital-to-IF converter (DIF), is truly versatile. It is capable of performing with radio standards from Bluetooth (narrow band and low dynamic range) through WiMax and Wireless USB (wide band and high dynamic range).

The Kaben on-die tunable filter has a tunable center frequency up to 1 GHz, a selectable bandwidth up to 40 MHz, and an adjacent channel rejection down to 60 dB. The Kaben synthesizer achieves a phase-noise level of -224 BFM and a spurious response of -90 dBc, at center frequencies up to 6 GHz. Additionally, Kaben's digital-to-IF converter provides a real IF output up to 100 MHz with a bandwidth up to 40 MHz.

In a truly reconfigurable transceiver, adjustable analog filtering in the receiver minimizes the dynamic range and bandwidth required by the A/D's. Further, if this IF filtering can be achieved on-die, at an appropriate, selectable IF frequency and bandwidth, then the classical, robust, super-heterodyne architecture can be implemented. The heterodyne architecture eliminates the difficulties of IP2, DC offsets, and 1/f noise associated with a low IF or a zero IF architecture, while allowing good frequency planning to avoid inter-modulation products.

In a similar manner, a direct digital-to-IF converter in the transmitter of a reconfigurable transceiver can eliminate the need for I & Q amplitude and phase tracking loops. Further, a direct digital-to-IF converter can easily incorporate the "look-up table" coefficients needed to invoke adaptive pre-distortion correction for the transmitter power amplifier. These coefficients, in turn, can be obtained from a second Sampling IF filter connected to the power amplifier output in a linearization "sense" path.