Improved accuracy and low-sensitivity design of digital allpass based hilbert transformers

In this paper, a very efficient approach to extend the frequency range over which the allpass-based digital Hilbert transformers phase difference is kept near constant and to reduce the deviation of the phase from 90° in a limited wordlength environment is proposed. This approach is based on minimization of the phase sensitivity of each individual allpass section in the cascade realization of the two branches of the parallel allpass structure, depending on their transfer function pole positions. The new results are verified by examples and experiments.