Measurements of Self-Loop Functions in High-Order Passive and Active Low-Pass Filters

This paper discusses the practical measurements of self-loop functions in second-order low-pass filters based on an alternating current conservation technique. From the view point of transfer function of a network, the measurement of phase margin at unity gain of the self-loop function can verify the operating region of a high-order transfer function which can be over-damping, or critically damping, or under-damping. The overshoot and undershoot voltages will occur in both passive and active linear systems when they work on the under-damping region. Therefore, measurements of self-loop function have been useful not only in passive networks but also in feedback systems.