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US 6,366,161 B1Granted
Active filter circuit
AssigneeNEC Corporation
InventorShinichi Koazechi
Life of this patent
Estimating the term…
Abstract
An active filter has a least an operational amplifier, a plurality of resistances and a plurality of capacitances, at least one of the resistances and the consequences is variable by controlling a controller connected to an output side of the active filter for receiving an output signal so that the controller counts a frequency of the output signal to generate a counted value so as to control the variable resistances and capacitances on the basis of the counted value.
Claims9
An active circuit comprising:
- a filter output terminal;
- an operational amplifier having an output connected to said output terminal;
- a first circuit being connected to input terminals and an output terminal of said operational amplifier, said first circuit including plural resistive elements and plural capacitive elements;
- and
- plural switching elements incorporated in said first circuit for configuring said active circuit as a selected one of a filter circuit and an oscillation circuit,
- wherein at least one of said resistive elements and capacitive elements comprises a variable element with a variable value, and
- said variable element is arranged to be variably controlled by a control circuit to re-set the variable value close to a predetermined value on a basis of a frequency of an oscillation output signal from said oscillation circuit when said oscillation circuit is configured by said switching elements.
4 more elements
Dependencies are inferred from the claim text.