A filter compiler under pressure: unusual approximations and realisations

The demands upon filter compilers continue to increase. Mixed-mode signal processing systems extend over an enormous frequency range and generate filter specifications which range from the sublime to the ridiculous (almost). Some specifications can be met by traditional approximation and filter realisation; others need the application of very powerful approximators and efficient circuit realisations to produce solutions that are viable as integrated circuits without impossible demands for chip area and power consumption or degradation in circuit performance due to accuracy problems or noise behaviour. The XFILT software provides a comprehensive active filter compiler which is finding application in areas where signal filtering and delay equalisation is required. It has been used in the real design world over a wide range of frequencies and it is hoped that further extensions will enlarge the field of application