On the theoretical design of a fractional feedback active NGD circuit

This work deals with a design theory of fractional feedback active (FFA) topology of low-pass (LP) type Negative-Group-Delay (NGD) circuit. The considered FFA topology operates with attenuation from a plant LP-NGD passive cell compensated by a direct chain amplifier. The design concept uses the FFA structure, including an LP-NGD passive cell acting as the plant circuit, a tunable direct gain stage and a resistive passive L-shape cell representing the negative feedback path. The feedback stage enables to overcome several design challenges, including the tunability via the plant cell, amplifier block or also the feedback passive cell by using off-the-shelf circuit components. To verify the theoretical concept’s feasibility, a proof-of-concept (POC) is designed and simulated. Results showing an LP-NGD value of about −2.5 μs having 24-kHz cut-off frequency with 0-dB gain confirm an excellent agreement between theory and simulation. The LP-NGD signature is verified by up to −1.9 μs time-advances of Gaussian and arbitrary waveform signals with transient analysis. As a result of parametric simulation analysis, the LP-NGD characteristics can be adjusted by the tunable gain stage and feedback stage without any alteration of the plant circuit parameters. The LP-NGD figure-of-merit of the circuit is improved by using the FFA topology.