NONLINEAR MULTIPLE BANDSTOP FILTER

Publishing Venue

Motorola

Related People

Abstract

ADVANTAGE OF USING A NONLINEAR MULTIPLE BANDSTOP FILTER CIRCUIT: Electronic low-frequency signal paths often are affected by unwanted periodic noise as i.e. created by power-supply rectifier harmonics, dimmer circuits or by low-frequency (PL) control-tone harmonics.

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Technical Developments Volume 22 June 1994

NONLINEAR MULTIPLE BANDSTOP FILTER

by Stefan Lichtetfeld

ADVANTAGE OF USING A NONLINEAR MULTIPLE BANDSTOP FILTER CIRCUIT:

PROBLEM DESCRIPTION

  Electronic low-frequency signal paths often are affected by unwanted periodic noise as i.e. created by power-supply rectifier harmonics, dimmer circuits or by low-frequency (PL) control-tone harmonics.

  Here a solution is described to blank periodic noise, while not significantly influencing the signal information.

  Prior methods to reduce the noise content on signal paths are to reduce the bandwidth by adding highpass or lowpass filters or set a bandstop filter on the most critical noise Frequency to damp this range. These solutions affect the waited signal and limit the possible improvement.

  The best performance is achieved by creating several bandstops on all critical noise-frequencies in the signal-frequency band. These bandstops should only suppress small signal levels as the expected noise content. In practice this may be done by choosing a suitable design and running the bandstop filter just below its amplifier limitation and using an active filter approach with high AC-gain: Figure 2.

  A phase inverting active bandpass for each unwanted frequency may add its output signal to the linear input signal at a summing node.

FIGURE 2-CASCADABLE NONLINEAR ACTIVE BANDSTOP FlLTER CIRCUIT

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