Design and Implementation of a Sigma-Delta Modulator in the Frequency Synthesizer
Liu De-jian · Computer Engineering and Science · 2009
The principle of the sigma-delta modulation technology is introduced first in this paper. Then the first-order and the higher order sigma-delta modulators are analyzed,and finally a method for the sigma-delta modulator based on FPGA is proposed. This design of a sigma-delta modulator is correct and feasible. Simulation results show that the results from the sigma-delta modulator and the fractional-N divider by controling the frequency divider implemented by this method are well in accordance with the simulation results based on Matlab software. Then noise shaping characteristics of the higher-order sigma-delta modulator is further experimentally verified. The fractional spur introduced by the fractional-N frequency synthesizer can be suppressed by the loop filter of the phase-locked-loop,which is highly practicable.