Amplitude Stability Detection of Sinusoidal Excitation Signal for High Precision Sensors

This article presents a high-precision detection method based on biased operational rectifier (BOR) and tracking analog-to-digital converter (ADC) for real-time monitoring of the amplitude drift of sinusoidal excitation signals, which significantly reduces the requirement for ADC's measurement accuracy and improves the signal-to-noise ratio (SNR). BOR modules are proposed innovatively to make the amplitude drift can be detected easily by an ADC with poor precision. Combining with the tracking ADC, the proposed detector could suppress the noise near the cut-off frequency and, thus, improve SNR. An amplitude drift detector and a lock-in amplifier are designed and tested experimentally. The results show that the voltage resolution of the proposed detector could reach 0.12 ppm for a sinusoidal source with an amplitude of 2.5 V. The SNR is measured 88 dB, which is 8 dB higher than that of the lock-in amplifier. The proposed detector is also applied in a precision capacitive displacement sensor. With the amplitude drift detector, the drift of the capacitive sensor caused by the signal source's amplitude drift could be significantly reduced from 16 to 2 nm/°C. Furthermore, this method is also applicable to other amplitude-modulated types of high-precision sensors.