Circuits and methods for removing a gain offset in a magnetic field sensor

摘要

A magnetic field sensor and a method include a modulator coupled in a feedback arrangement and operable to modulate a calibration feedback signal with a modulator clock signal having a selected frequency and a selected relative phase operable to remove a gain error in the magnetic field sensor and in the method.

主权项

1. A magnetic field sensor, comprising:
two or more Hall effect elements coupled together for generating a Hall effect element signal having a magnetic field component and an offset component, the magnetic field component responsive to an external magnetic field; a switching circuit coupled to the Hall effect element and configured to generate a chopped signal representative of a four phase current spinning of the Hall effect element, the four phase current spinning having four phases including a first phase, a second phase following the first phase, a third phase following the second phase, and a fourth phase following the third phase, the four phases periodically repeating, wherein changes between the four phases occur at a phase rate; a first modulator coupled to the chopped signal and configured to modulate a signal related to the chopped signal with a first modulator clock signal, wherein the first modulator clock signal has a first frequency for which changes of states of the first modulator clock signal occur at the phase rate; a channel amplifier coupled to the first modulated signal, coupled to a gain adjustment signal, and configured to generate an amplified signal having a gain responsive to the gain adjustment signal, wherein the gain of the channel amplifier has a gain average component and a gain offset component; a second modulator coupled to the amplified signal and configured to modulate a signal related to the amplified signal with a second modulator clock signal having the same first frequency to generate a second modulated signal; an error amplifier coupled to a calibration signal, the calibration signal representative of a measured sensitivity of at least a portion of the magnetic field sensor in response to a calibration magnetic field, the error amplifier operable to compare the calibration signal to a reference signal to generate a comparison signal; a third modulator coupled to the comparison signal and configured to modulate a signal related to the comparison signal with a third modulator clock signal having a second different frequency equal to the first frequency divided by two to generate a third modulated signal, wherein a first state of the third modulator clock signal occurs during the second and third phase of the four phases and a second state of the third modulator clock signal occurs during the first and fourth phases of the four phases, wherein the gain adjustment signal received by the channel amplifier comprises the third modulated signal; and a filter coupled to the second modulator signal and operable to generate a magnetic field sensor signal responsive to the external magnetic field, the magnetic field sensor signal responsive the external magnetic field, the magnetic field sensor signal having an amplitude more responsive to the gain average component than to the gain offset component.