Accuracy improvement of real-poles allpass-based digital Hilbert transformers

In this work a very efficient approach to extend the frequency range over which the real-poles allpass-based digital Hilbert transformers (HT) phase difference is kept near constant and to reduce the deviation of the phase from 90o in a limited word-length environment is proposed. This approach is based on minimisation of the phase sensitivity of each individual first- and second-order allpass section in the cascade realisation of the two branches of the structure used, depending on their transfer function pole positions, including replacements of second-order-sections by two first-order low-sensitivity allpass sections. The effectiveness of the proposed design is experimentally verified and the HTs so obtained are very suitable for different telecommunication applications.