Patent attributes
A phase-measuring delta-sigma modulator calibration method and apparatus provides for adjustment of the modulator noise transfer function (NTF) of the modulator in operational environments. A signal is injected into the feedback loop of the delta-sigma modulator either before or after the quantizer and the phase of the noise transfer function is measured by phase comparing the injected signal and quantizer output, which is first filtered with a narrow-band filter to remove other quantization noise or signal components. The delta-sigma modulator has adjustable coefficients that are adjusted in conformity with the phase-measurement to achieve a more desirable noise transfer function. Quadrature detection may be employed, with filtering provided by digital filters already present in an ADC converter for output filtering, or accumulators may be included to perform the phase accumulation. The signal generation and phase measurement may be at the zero of the NTF.
