Maciej Borkowski

A practical /spl Delta/-/spl Sigma/ modulator design method based on periodical behavior analysis

A method for digital delta-sigma modulator design for fractional-N frequency synthesis is presented in this paper. The design method is based on the modulator periodical behavior analysis. The modulator is designed to maintain a constant output signal sequence length which can be controlled for all input dc levels. As a result, the quantization noise power is spread over a known, arbitrarily large number of tones within the Nyquist bandwidth. Therefore, the quantization noise power never concentrates into a few dominant spurious tones. The sequence length is controlled by applying predefined initial conditions and scaling modulator buses. Consequently, the spurious-free range can be controlled as a function of the bus width. Known modulator sequence length defines the time required for full modulator and synthesizer characterization.

Spurious tone free digital delta-sigma modulator design for DC inputs

A method for spurious tone free delta sigma modulator design is presented. The method is based on an analysis of modulator state space orbits and it is applicable to digital modulators working with DC inputs. The modulator is designed to maintain very long controllable sequence lengths. This results in a smooth distribution of the quantization noise power and prevents it from concentrating into spurious tones. The sequence length is controlled by modulator scaling and applying initial conditions each time the DC input changes. A list of suitable initial conditions and corresponding sequence lengths is given for MASH and error feedback modulators. This method is extended further to a more flexible case in which reloading initial conditions is no longer necessary. It is shown that when modulator resolution is increased by one bit and initial conditions applied at startup, the modulator spontaneously enters very long orbits each time the DC input changes. In return for the small hardware increment, the spectrum remains smooth and is further decreased by 8 dB.

On randomization of digital delta-sigma modulators with DC inputs

This study compares a recently proposed deterministic modulator design method to a design based on dithering. The recent method is based on a delta-sigma modulator periodical behavior analysis. Three different dither generators were used in the study: a linear shift register, rectangular and triangular probability density function random number generators. The study shows that the new method gives as good spectrum as resulting from using the best dither generator, while consuming less hardware

Modulator evaluation method in /spl Delta/-/spl Sigma/ fractional-N frequency synthesis

The choice of a /spl Delta/-/spl Sigma/ modulator architecture has a significant impact on the performance of the /spl Delta/-/spl Sigma/ frequency synthesizer. The paper focuses on a modulator design method that allows full modulator and synthesizer characterization. It is shown that the MASH architecture can be designed to maintain a constant, arbitrarily long, output sequence for each input DC value. A modulator designed in such a way spreads the quantization noise over a known, arbitrarily large number of tones within the Nyquist bandwidth. Post modulator filtering is considered as a case study.