RC Allpass Delay Filter

This technical report presents the development of a simple envelope, or group, delay filter whose magnitude response emulates allpass characteristics for relatively broad frequency passbands. Unlike traditional allpass delay networks, the filter presented herewith exploits no inductances and maintains a common ground between its input and output ports. The absence of circuit inductances simplifies the monolithic realization of the filter, while its three-terminal common ground architecture maximizes its utility in a ubiquity of communication and other electronic system applications. The report offers definitive circuit analyses that culminate in detailed electrical models for the filter input and output ports, design criteria for ensuring an acceptable emulation of allpass magnitude responses, and clear design strategies aimed toward achieving stipulated input/output (I/O) group delays over maximally broad signal frequency ranges.