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This lecture covers ideal operational amplifier circuits, including voltage adding circuits, integrators, differentiators, phase shifters, negative impedance converters, gyrators, and the Mason signal flow graph.
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CIRCUITS and SYSTEMS – part II Prof. dr hab. Stanisław Osowski Electrical Engineering (B.Sc.) Projekt współfinansowany przez Unię Europejską w ramach Europejskiego Funduszu Społecznego. Publikacja dystrybuowana jest bezpłatnie
Lecture 14 Operational amplifier circuits
Ideal operational amplifier • Infinite gain A • Zero output impedance • Infinite input impedance • These features valid for frequency from 0 to infinity.
2-port model of ideal op-amp Hybrid description
Voltage adding circuit - equations Kirchhoff’s equations After simplification we get
Integrator Transfer function
Differentiator Transfer function
Phase shifter Kirchhoff’s equations
Phase shifter (cont.) The currents Output voltage Transfer function
Negative impedance converter (NIC) Kirchhoff’s equations Chain matrix description
Gyrator Kirchhoff’s equations Admittance matrix description
Mason signal flow graph (SFG) Basic notions: • Node – the point of graph associated with variable x • Branch – the directed arch joining 2 nodes • Gain – the transfer function describing branch • Loop – the sequence of identically directed branches forming closed loop • Gain of the loop – the product of gains of branches of the loop • Source node – the node from which the branches can only start • Cascade – the sequence of identically directed branches from the source node to the output node.
Example of SFG Set of linear equations Transformation to Mason form Mason SFG
Mason gain formula Transfer function Δ - main determinant of SFG Gains of all loops Gains of non-touching loops Tk – gain of kth cascade from source to output node Δk - determinant of graph after eliminating kth cascade from SFG
Example Graph Transfer function
Direct construction of SFG for passive elements connection Circuit Its SFG
Direct construction of SFG for op-amp Op-amp Its SFG
SFG of the circuit After simplification at we finally get