Apparatus and method for compensating output signals of magnetic encoder using digital phase-locked loop

An apparatus for compensating output signals of a magnetic encoder, comprising:

• a pre-calibration unit configured to obtain two phase-compensated waveforms having an identical phase through trigonometric function operations of normalized waveforms of digitally converted sine and cosine waves, which are converted from ME (magnetic encoder) output sine and cosine waves output from a magnetic encoder, and configured to adjust amplitudes of the two phase-compensated waveforms to an identical value, thereby generating input sine and cosine waves having the same phase and the same amplitude;
• an advanced phase detector configured to generate an error output signal having information about a phase error between a phase of the input sine and cosine waves and an estimated phase of the compensated sine and cosine waves;
• a loop filter configured to filter the error output signal using an active lead-lag filter having a filter transfer function set based on a natural frequency and a damping factor;
• a VCO configured to generate the compensated sine and cosine waves having the estimated phase based on the filtered error output signal;
• and
• a pulse generator configured to generate two output pulses so as to have predetermined pulse levels and a phase difference of 90 degrees, corresponding to a current phase index, selected among multiple fractionized phase indices obtained from fractionizing a full range of phase within a single period of the compensated sine or cosine wave.

A method of compensating output signals of a magnetic encoder, comprising:

• obtaining two phase-compensated waveforms having an identical phase through trigonometric function operations of normalized waveforms of digitally converted sine and cosine waves which are converted from ME (magnetic encoder) output sine and cosine waves output from a magnetic encoder, and adjusting amplitudes of the two phase-compensated waveforms to an identical value, thereby generating input sine and cosine waves having the same phase and the same amplitude;
• generating an error output signal through trigonometric function operations of the input sine wave, the input cosine wave, and a compensated sine wave and a compensated cosine wave having an estimated phase, so that the error output signal has a sine term, as a multiplying term, of a phase error between a phase, of the input sine wave and the input cosine wave, and the estimated phase, of the compensated sine wave and the compensated cosine wave;
• setting a filter transfer function of an active lead-lag filter based on a natural frequency and a damping factor determined based on the error output signal and overshoot, and filtering the error output signal using the active lead-lag filter;
• generating a compensated signal including the compensated sine and cosine waves having the estimated phase based on a signal obtained by passing the filtered error output signal through an integrator having a predetermined gain;
• and
• outputting a phase index, corresponding to a current phase of the compensated sine and cosine waves, selected among multiple fractionized phase indices obtained from fractionizing a full range of phase within a single period of the compensated sine and cosine waves, and generating two output pulses having a phase difference of 90 degrees in accordance with a pulse generation rule found in a look-up table, based on the phase index of the current phases, the look-up table storing pairs of size values of frequency-multiplied sin and cosine waves assigned to each of the phase indices.