The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Apr. 03, 1979
Filed:
Jun. 20, 1977
Alan J Greaves, Needham Market, GB;
The Post Office, London, GB;
Abstract
A construction of an active filter having the same characteristics as a predetermined passive filter is described in which the capacitors of the passive filters are replaced by a topologically equivalent first network of resistors and the inductors of the passive network are replaced by a topologically equivalent second network of resistors, the two networks of the resistors being interconnected in a manner corresponding to the connections in the passive filter and connected to points corresponding to interconnection points of the passive filter by means of negative impedance converters, the converters connected to the first network having conversion ratios effective to convert resistance into negative capacitance and the converters connected to the second network having conversion ratios effective to convert resistance into negative inductance. The input and output to the active filter may be through similar negative impedance converters or may be directly to points in one or other resistive networks. An additional resistor connected between points of the active filter which correspond to terminals of a resonance circuit in the passive filter can provide Q-factor enhancement. A suitable design of negative impedance converter uses an operational amplifier the two inputs of which respectively form the input and output terminals of the converter with impedances connected from the output of the amplifier to its inputs.