Akerberg-Mossberg Biquad

The Akerberg-Mossberg biquad exceeds the performance of the Thomas biquads for opamp imperfections and matches the Thomas 2 biquad notch performance in the presence of element value errors. This increased performance is obtained by replacing the positive integrator in the Thomas 2 biquad second and third opamps with a Miller integrator. The Miller integrator uses two matched opamps in a configuration that tends to cancel errors due to opamp imperfections.

The output of the Akerberg-Mossberg biquad may be from any of the three opamps.

Akerberg-Mossberg Biquad

 

Miller Integrator

The opposing second and third opamps in the Akerberg-Mossberg biquad shown above constitute the Miller integrator. The outputs of the two opamps are equal and opposite. If matched opamps are used in the Miller integrator, this opposing arrangement tends to cause errors due to opamp imperfections to cancel, and thereby create a high quality output signal for the biquad as a whole.

Biquad Advantages Disadvantages

Akerberg-Mossberg

  • Highest tolerance to opamp imperfections of all biquads available in FilterSolutions.

  • Notch quality is immune to element value error just as in the Thomas 2 biquad.

  • Low pass sign change capability.

  • Sometimes three capacitors are required as opposed to only two for the Thomas 1 biquad.

  • Three opamps are required as opposed to the one and two opamp biquad designs.

  • Sign is fixed for high pass, band pass, notch, and all pass stages.