US PATENT SUBCLASS 327 / 552
.~.~ Active filter

Current as of: June, 1999
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327 /   HD   MISCELLANEOUS ACTIVE ELECTRICAL NONLINEAR DEVICES, CIRCUITS, AND SYSTEMS

524  DF  SPECIFIC IDENTIFIABLE DEVICE, CIRCUIT, OR SYSTEM {22}
551  DF  .~ Unwanted signal suppression {1}
552.~.~ Active filter {5}
553  DF  .~.~.~> Adjustable {2}
556  DF  .~.~.~> Notch or bandreject
557  DF  .~.~.~> Bandpass
558  DF  .~.~.~> Lowpass
559  DF  .~.~.~> Highpass

DEFINITION

Classification: 327/552

Active filter:

(under subclass 551) Subject matter wherein a specified frequency or a range of frequencies of an input signal is passed or blocked by the use of an active device.

(1) Note. Filter circuits that do not include any active element, such as a transistor, an amplifier, etc., and are constituted by distributed parameters, lumped parameters, long line elements, or passive elements (resistors, capacitors, or inductors) are excluded from this subclass and are classified primarily in Class 333, Wave Transmission Lines and Networks.

(2) Note. Filter circuits involving a systematic operation on data which results in a significant change in data are classified elsewhere.

SEE OR SEARCH THIS CLASS, SUBCLASS:

311, for transient or signal noise reduction in a filtered limiting, clipping, or clamping circuit.

379, for a gating circuit with spurious noise override.

SEE OR SEARCH CLASS

181, Acoustics, 175+, for sound filters.

307, Electrical Transmission or Interconnection Systems,

105, for a class appropriate harmonic filter or neutralizer.

333, Wave Transmission Lines and Networks,

28, for equalizers, subclasses 165, 166, and 167+ for frequency or time domain filters, subclass 202+ for wave filters including long line elements.

340, Communications: Electrical,

825.71+, for selective communication systems which are frequency responsive.

363, Electric Power Conversion Systems,

39+, for conversion systems in combination with a filter.

375, Pulse or Digital Communications,

103, for noise filtering in a digital receiver. 708, Electrical Computers: Arithmetic Processing and Calculating,

300+, for filtering of data by a digital calculating computer and subclass 819 for analog computer filtering.