Signal Extraction
Synchronous extraction of double-frequency excitation signals yields precise magnetic flux measurements in saturation sensors. Executing second harmonic demodulation involves driving a soft magnetic core into positive and negative saturation with an AC excitation field of frequency f, then filtering the pickup voltage to extract the 2f harmonic frequency component. The amplitude of the second harmonic component is directly proportional to the external DC magnetic field strength.
Phase-sensitive detectors multiply pickup signals by a double-frequency reference clock to produce a DC output voltage. Phase alignment errors between reference signals and pickup harmonics degrade measurement linearity and sensitivity. Calibration protocols align reference phases inside zero-field magnetic shields.
Phase Detection
Phase-locked loops generate coherent double-frequency reference clocks aligned with excitation drivers. Quadrature phase alignment maximizes demodulated DC voltage output while rejecting odd-harmonic interference. Calibration adjusts reference phase delays to achieve maximum sensor sensitivity.
Synchronous detection isolates low-amplitude magnetic signals from background electrical noise.
Carrier Rejection
Bandpass filters remove fundamental excitation frequencies and odd harmonics prior to signal demodulation. Suppressing fundamental excitation carrier signals prevents amplifier saturation in high-gain output stages. High filter attenuation improves signal-to-noise ratios in weak magnetic field detection circuits.
Bandpass verification tests measure rejection ratios at fundamental frequencies.
Calibration Accuracy
Precision reference magnetic fields generated by Helmholtz coils calibrate demodulator output voltages. Linearity testing verifies proportional voltage response across target magnetic field ranges. Demodulation performance limits set maximum detectable field bandwidths.
