Amplifier Design for Specified Frequency Response Profiles Using Nullors–Hearing Aids, a Case Study

Applications of nullors and fixator-norator pairs (FNP) for designing amplifiers with certain frequency profiles are discussed. The paper is focused on the design of front-end or stand-alone analog amplifiers that are used in hearing aids. For a given hearing profile (audiogram), a circuit called an audiogram generator circuit (AGC) is initially constructed to produce a frequency response similar to that of an actual audiogram. The hearing aid amplifier is then designed next. As demonstrated, the amplifier is constructed by a combination of an FNP with an AGC. This causes the frequency response of the amplifier to be the inverse of that of the AGC. Hence, the voice received is amplified in such a manner that the patient hears and comprehends a flat and uniform voice for the entire dynamic range. In the second part of this paper, a more advanced design procedure is discussed. The amplifier so designed is capable of producing a specified (non-flat) final hearing profile. Finally, an alternative methodology using feedback theory is discussed in the Appendix. It is shown that with proper buffering this design can also produce a flat hearing profile, as well.