Sigma-delta modulator

Abstract

A Sigma-Delta (ΣΔ) modulator for converting an analog input signal having a frequency bandwidth around a variable center frequency fto a digital output signal at a sampling frequency f. The ΣΔ modulator comprises a quantizer () for generating the digital output signal and a loop filter for shaping the quantization noise. The loop filter comprises at least one subfilter () centered around a frequency fand constant noise shaping coefficients (). The ΣΔ modulator further comprises a tunable delay element (), a frequency adjuster () for adjusting the sampling frequency fsuch that the normalized center frequency f/fis constant, and a delay adjuster () for adjusting the loop delay timplemented by the quantizer and the tunable delay element (), such that the normalized loop delay t/Tfalls in a predetermined range [t, t], where T=1/f.