Single-amplifier active filters realize a general second-order (biquadratic) transfer function — characterized by pole frequency, pole selectivity (Q), zero frequency, zero selectivity, and gain constant — through positive-feedback (Sallen-Key), negative-feedback (multiple-feedback), and enhanced-negative-feedback (negative feedback with added positive feedback) RC-network topologies around a single op-amp, yielding low-pass, high-pass, band-pass, band-reject, or all-pass responses depending on which transfer-function coefficients are nonzero. This belongs to active-filter design theory in analog signal-conditioning circuits, applying feedback and pole-zero analysis plus sensitivity theory to realize frequency-selective networks cheaply, at the cost of high element sensitivity and lack of independent (orthogonal) tunability of filter parameters.
Single-amplifier active filters realize a general second-order (biquadratic) transfer function — characterized by pole frequency, pole selectivity (Q), zero frequency, zero selectivity, and gain cons…