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US 6,680,645 B2Granted
Active filter circuit with operational amplifier
AssigneeMicronas GmbH
InventorsNorbert Greitschus, Stefan Noe
Life of this patent
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Abstract
An at least second-order active filter circuit includes an operational amplifier (Op) whose frequency response, in conjunction with an RC network (R1, R2, C1, C2), serves to set a predetermined low-pass characteristic. The frequency response of the operational amplifier (Op) forms an integral part of this low-pass characteristic.
Claims2
An active filter circuit having a signal input (L1), said active filter circuit comprising:
- an operational amplifier (Op) that includes a transconductance amplifier having a transconductance (gm) controlled by a bias circuit to be inversely proportional to a value of a transconductance determining resistor Rb within said bias circuit, wherein said operational amplifier (OP) has a frequency response that has a low-pass characteristic controlled by said transconductance (gm);
- an RC network that includes
- a first resistor (R1) connected between the signal input (L1) of said filter circuit and an inverting input of said operational amplifier (Op), and a first capacitor (C1) connected between said inverting input and a fixed reference potential;
- a second resistor (R2) and a second capacitor (C2) connected between said inverting input and an output of said operational amplifier (Op), which output also forms the signal output of said filter circuit;
- and
- a noninverting input of the operational amplifier (Op) is connected to the fixed reference potential.
3 more elements
Dependencies are inferred from the claim text.