| Delta-Sigma converters used in synchronous demodulation sensing applications contain zeroes in the Noise Transfer Function (NTF) for aggressive noise shaping; however, analog component errors typically result in misplacement of the notch frequency resulting in lower SNDR and reduced sensor sensitivity. The error detection technique proposed here corrects for the analog errors in the digital domain by injecting a single tone directly at the input of the quantizer inside the loop of the Delta Sigma Modulator (DSM) and monitoring the RMS output in the digital domain. A closed loop least mean squares (LMS) algorithm adjusts the sampling frequency of the modulator until the tone strength is reduced to a minimum, which corresponds to the accurate placement of the notch. Simulation results have demonstrated an improvement of 20 dB for a Single-Loop, Third-Order CIFB (Cascade of Integrators, Feedback Form), single-bit quantizer, delta sigma modulator with an oversampling ratio (OSR) of 128 and a notch filter coefficient error of 50%. The technique is highly suitable for applications where high-Q resonators are employed, such as in tuning fork gyroscopes. |
