Multi Coil Quadrature Demodulation Signal Chains for Proximity Measurement
Multi coil quadrature demodulation isolates amplitude and phase in inductive proximity chains, resolving sub-micron targets while rejecting thermal noise.
I/Q Signal Processing
Vector Signal Decoding
Demodulation of complex waveforms into two orthogonal components allows for the simultaneous measurement of magnitude and phase. Hardware or software using i/q signal processing splits an incoming carrier into an in phase part and a quadrature part shifted by ninety degrees. This technique is fundamental to modern communication systems.
It provides a complete description of how a target interacts with a magnetic field.
Mixer Topology
Two separate multipliers receive the raw input signal alongside reference signals from a local oscillator. One branch uses a sine wave while the other uses a cosine wave. Then i/q signal processing filters the outputs to remove the high frequency sum products, leaving only the low frequency difference terms.
This process preserves the vector information required to distinguish between different material properties.
Data Extraction
Calculating the square root of the sum of the squares of the two components yields the signal amplitude. The inverse tangent of the ratio between the parts provides the phase angle. Because i/q signal processing handles these as vectors, it can identify the specific signature of a flaw or a distance change.
Digitizing the components separately allows for advanced filtering in the digital domain.
Error Source
Mismatches between the two channels lead to errors in the calculated phase and magnitude. If the gain of the in phase branch is higher than the quadrature branch, the resulting vector plots as an ellipse instead of a circle. Periodic calibration compensates for these hardware offsets.