Abstract: Recently the Sigma-Delta modulator has been widely used in communication.One of the applications is to digitize the signal at intermediate frequency in a super-heterodyne receiver with a band-pass Sigma-Delta modulator.A band-pass Sigma-Delta modulator with a bandwidth at 1.25 MHz and a center frequency 20 MHz is designed, and a new modulator structure and its coefficient computing method are proposed.This structure is insensitive to coefficients variation, and its resonators' swing is low, thus lowering the requirement in the design of the operational amplifier.Simulation results indicate that the peak signalnoise-distortion-ratio of the modulator is 60 dB, and its dynamic range is 62 dB.

Key words: transfer function, structure coefficient, band-pass, Sigma-Delta