Demodulation Technique
Signal processing techniques that split a modulated sinusoidal carrier into two orthogonal components allow for the simultaneous measurement of amplitude and phase shift. This procedure, termed IQ demodulation, multiplies the incoming signal by both an in-phase reference and a quadrature reference shifted by ninety degrees. The resulting low-pass filtered outputs represent the real and imaginary parts of the sensor signal.
Phase Extraction
The phase angle is calculated by taking the arctangent of the ratio between the quadrature and in-phase components. This provides an unambiguous angle over a full circle.
Calibration Procedure
Gain differences or phase offsets between the two signal paths will cause measurement errors. During the calibration phase of the instrument, a test signal of known phase is applied to the receiver to map and correct these internal imbalances. This correction ensures that the IQ demodulation process maintains high linearity across the full dynamic range of the system.
Metrological Error
Analog components introduce amplitude imbalance and phase errors that limit the precision of the measurement. These errors are minimized by implementing the demodulator digitally inside a processor or gate array. A digital demodulator can achieve a phase accuracy better than zero point zero five degrees.
