An adaptive phase equalizer for minimum phase SAW filters

Standing acoustic wave (SAW) filters are used in many types of digital receivers, a majority of which are wireless telephones. Most of these filters are designed to have a linear-phase response so that the transmitted pulse can pass through undisturbed while out-of-band noise and adjacent channels are rejected. If the linear-phase specification is removed, the potential exists for smaller and less expensive filters to replace their linear-phase counterparts. This paper describes one particular minimum-phase SAW filter which is suitable for use as the intermediate-frequency filter (IF) in a wideband spread-spectrum receiver. In order to correct for the phase nonlinearity of the SAW filter, a digital adaptive phase equalizer algorithm is proposed. The decision-directed algorithm (DDA) and constant modulus algorithm (CMA) are considered for automatic adjustment of the phase equalizer.