Building a FM/AM Tuner with Kaben’s Products and Technology
Until a few years ago, FM tuners were essentially analog designs. However, with the advent of mixed signal integrated circuits, and with the introduction of new FM features such as RDS (Radio Data System) which provides associated text annotation to the music being currently played, FM Tuner technology has undergone a major transformation. Many of the functions in a modern FM tuner are now performed digitally. However, existing product offerings still require external SAW (Surface Acoustic Wave) RF filters. In addition, the digital functions of these FM tuners are realized in dedicated digital hardware, and are not able to reconfigure their parameters to optimize their reception in a congested or strongly fading channel.
Kaben has invented a wholly new type of RF filter based on RF sampling techniques. This SIF (Sampled IF Filter) can be integrated with the other blocks of the FM tuner onto a single silicon die, thereby removing the need for, and extra cost of, external components. This filter not only achieves excellent (SAW like) filtering performance, it is exceedingly robust to semiconductor process variations, and temperature changes. Further, the filter is programmable in bandwidth and center frequency, enabling adaptive reception to different FM channels. Inclusion of this novel RF filter into an FM tuner significantly reduces the cost of the BOM (Bill of Materials). Further, for the first time, it enables an FM tuner to be integrated as a secondary function onto a CMOS die, with the host function being, for example, an MP3 player.
Kaben’s end-to-end system design of an all digital FM tuner has culminated in the design of the programmable Sampled IF Filter (dependent on the deviation measured), an equalizer (to compensate for the sin x / x roll-off of the filter), a digital AGC (Automatic Gain Control), a digital Hilbert Transformer, a complex phase-locked loop demodulator (and deviation measurer), a pilot tone phase-locked loop (and lock indicator), the L-R (Left minus Right) down-converter, the RDS (Radio Data System) demodulator, the MPX (soft mute / fast mute / stereo blending), the post-detection deemphasis, and the after stereo blending and filtering.
All key RF blocks, including the RF filters, are implemented in CMOS technology, and all key back-end blocks are implemented in real-time code running on a commercial CMOS processor. This yields an FM tuner with a reduced product cost (due to the integrated RF filter) and an increase in performance (through its flexible response to channel congestion or fading).
The digital portion of the design can be delivered as C code for a software digital back-end or as Verilog as a custom digital back-end. The software back-end can be integrated with an existing microprocessor.
