Differential-current derived feedback in error-correcting audio amplifier applications

A dominant distortion mechanism in audio power amplifiers results from nonlinearity in the voltage and current transfer functions within the power output stage. A technique is presented that uses a magnetic differential sensor to sense this distortion and to apply a supplementary error-correcting feedback path within the amplifier, in addition to overall negative feedback. Differential-current derived feedback is explored and the technique is shown to be applicable to both voltage and current transfer errors. Analysis reveals the system alignment for obtaining a distortion null and these results are confirmed using nonlinear transient analysis. Basic system topologies are presented using voltage transfer and transconductance gain cells as an aid to complete amplifier synthesis. Comparisons are made with feedforward-feedback error correction where the current-dumping amplifier is reconfigured using differential-current feedback. Generalisations are made to a multi-loop nest of amplifiers using individually aligned error correcting paths to achieve corresponding improvements in distortion reduction