4.9 Conclusions

Log domain filtering is a very new area of active filter design. As a result, there are no generally accepted design procedures. The discussion in this chapter has therefore centred on familiarising the reader with the basic ideas and concepts related to this new idea. An attempt has been made to summarise several perspectives on the design of these filters, with the intent to give the reader an ability to not only appreciate how to go about designing log domain filters, but also access the literature for more information and perspective.

Hopefully, the discussion has also highlighted the main advantages and disadvantages of log domain filters. The main advantages of log domain filters involve their potential for new solutions to the hard problems associated with low voltage wide bandwidth filter design and in the new perspective the concept itself offers. Clearly, to the extent that log domain filters add 10 20 dB of dynamic range to active filters, they are of great interest. On the other hand, this increase in dynamic range is applicable only to a special class of transistor filters with already limited dynamic range compared to more classic voltage mode designs. Nevertheless, in cases where supply voltage, tunability or bandwidth necessitate a deviation from the old solutions, log domain filters are a very interesting alternative. From the perspective of pure science, the log domain concept is one of the most revolutionary ideas to be proposed in recent history. It is quite intriguing to suppose that nonlinearity...