A digital MASH 1-1-1 modulator with XOR-based dither for a feasible
digital synthesis
Abstract
The Digital Delta-Sigma Modulator (DDSM) has the disadvantage of
presenting a periodic output for constant inputs, affecting the benefits
of noise-shaping modulation. This work uses the linearized model to
expose the principal features of the recent solutions. The analysis
results in two ideas: the first is a mix of the Song-and-Park
Multi-stAge-noise-SHaping (SP-MASH topology) with the appropriate dither
elimination, another option is a MASH modified by applying an XOR based
dither to the input of the second accumulator. The work validates the
proposed solutions with the mathematical, the spectral, and the hardware
synthesis showing the benefit of the proposed schemes with the output
spectrum using a 9-bit implementation for each case. The results show
the idle tones do not appear for all the possible input values. The
hardware increase is 3 percent compared to the third order dithered
input SP MASH solution.