Abstract: The invention relates to digital signal processing and specifically to level control of a pulse density modulated (PDM) signal generated by a sigma-delta modulator. A single-bit pulse density modulated PDM signal is generated by a first sigma-delta modulator being an analog modulator, for instance. Level control is performed by multiplying the single-bit pulse density modulated PDM signal by a multibit multiplier to obtain a multibit number stream, which is reconverted into a single-bit PDM signal by a second digital sigma-delta modulator, as to the signal-to-noise ratio. Thus the most significant factor in the total signal-to-noise is the noise level of the first sigma-delta modulator, by which the PDM signal was originally generated. In the subsequent second sigma-delta modulator, the PDM signal can then be attenuated as much as is the difference between SNR performance of the modulators without any decrease in the total signal-to-noise ratio.

Abstract: The invention relates to an oversampled high-order modulator, especially a sigma-delta modulator, comprising cascaded integrators in a number corresponding to the order of the modulator, a quantizer, and a negative feedback. The problem with the high-order modulator is that the modulator is locked in an unstable mode from which it should be restored without considerably interfering with the operation of the modulator. The invention achieves this by temporarily changing the value of the negative feedback to a direction which will restore the stable operation.