Reduced Complexity, High Performance Digital Delta-Sigma Modulator for Fractional-N Frequency Synthesis

This paper presents the design consideration of high or-der digital AZ modulators used as modulus controller for fractional-N frequency synthesizer. A third-order MASH structure (MASH 1-2) is designed and implemented which allows for the input to operate over 75 % of the input adder capacity. The number of the output levels is reduced to two bits. The circuit was verified through simulation, ASIC im-plementation and exhibits high potential for a gigahertz range, low-power monolithic CMOS frequency synthesizer. 1