Sigma-delta modulator

A method for converting an analog input signal having a frequency bandwidth around a variable center frequency f0 to a digital output signal at a sampling frequency fs by a Sigma-Delta (ΣΔ) modulator, the ΣΔ modulator comprising a quantizer and a loop filter for shaping the quantization noise, the loop filter comprising at least one subfilter centered around frequency f0 and noise shaping coefficients,

• the method comprising,
• processing by the ΣΔ modulator said analog input signal for generating said digital output signal,
• the method being characterized in that:
• the processing is performed using constant noise shaping coefficients which are independent of the center frequency f0;
• the ΣΔ modulator further comprises a tunable delay element;
• and in that the method further comprises:
• adjusting the sampling frequency fs such that the normalized center frequency f0/fs is constant,
• adjusting the loop delay td implemented by the quantizer and the tunable delay element, such that the normalized loop delay td/Ts falls in a predetermined range [tmin, tmax], where Ts=1/fs.