Using finite impulse response feedback DACs to design ΣΔ modulators based on LC filters

This paper proposes a general method to design the noise-transfer-function of a continuous-time ΣΔ modulator having high-order passive LC loop filters. The feedback signals can have arbitrary shapes and can be applied either at internal nodes or only at the input node. As a design example, this technique is used to design a 4th order ΣΔ modulator where the internal nodes of the loop filter are removed for a more efficient circuit implementation.