Active Guarding Architecture for Capacitive Target Measurement under Moisture Shifts
Active guard architectures require closed loop phase alignment below 0.05 degrees to eliminate moisture induced stray capacitive leakage currents.
IQ Carrier Extraction
Demodulation Technique
Coherent signal recovery processes use phase-sensitive detection to separate complex modulated waveforms into orthogonal components. In precision sensing, IQ carrier extraction isolates the in-phase and quadrature components of the carrier signal. This process allows the system to measure both the amplitude and the phase shift simultaneously.
Signal Extraction
An analog or digital multiplier mixes the received sensor signal with a local reference carrier and a ninety-degree phase-shifted version of that carrier. Low-pass filters then remove the high-frequency mixing products, leaving only the slow-varying in-phase and quadrature outputs. These outputs correspond to the real and imaginary parts of the sensor impedance.
By analyzing these components, the processor can calculate the exact displacement while ignoring resistive losses.
Reference Calibration
System alignment procedures establish the correct phase relationship between the transmitter drive and the extraction receiver. This calibration involves using a reference standard with a known impedance to adjust the phase delay of the local carrier. This step must be performed under stable temperature conditions to prevent thermal phase shift in the routing traces from introducing calibration errors.
Ongoing verification compares the extracted phase against the calibrated reference value.
Operating Constraint
Frequency drift in the master oscillator can degrade the accuracy of the extraction process by introducing phase errors. If the transmit carrier frequency deviates from the local demodulator frequency, a continuous phase rotation occurs, which mixes the in-phase and quadrature channels. This channel crosstalk makes it impossible to distinguish between capacitive changes and resistive losses.
To prevent this, both the transmitter and the extraction receiver must be locked to the same high-stability clock source, and any changes in routing path delay must be compensated by dynamic tracking firmware.