SLYA085 December   2023 TMAG6180-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2AMR Angle Sensing
  6. 3Calibrating AMR
    1. 3.1 Input Related Errors
    2. 3.2 Sensor Related Errors
    3. 3.3 Offset
    4. 3.4 Amplitude Mismatch
    5. 3.5 Orthogonality Error
    6. 3.6 Noise
  7. 4Summary
  8. 5References

3.4 Amplitude Mismatch

Amplitude mismatch occurs with variations in channel sensitivity gain resulting in minor variations in the output amplitude of either the sine or cosine outputs. These variations skew the correct circular response shown in plot b of Figure 3-8.

The automatic gain control in TMAG6180-Q1 and TMAG6181-Q1 attempts to adjust channel sensitivity gain so the total magnitude is constant. However, some amount of mismatch can persist. Normalizing the two signals to the same amplitude removes this amplitude mismatch and minimizes this error source. This normalizing step occurs in post-processing using Equation 7 through Equation 9.

Equation 7. A s i n _ d i f f = sin d i f f ( m a x )   -   sin d i f f ( m i n )   2
Equation 8. A c o s _ d i f f = cos d i f f ( m a x )   -   cos d i f f ( m i n )   2
Equation 9. k = 1 -   ( A c o s _ d i f f   A s i n _ d i f f )