Rejection of Aliases for a Direct Sampling Mixer with Complex Poles

Abstract

This paper proposes the design scheme of direct sampling mixer (DSM) by which unallowable amplitude characteristics due to aliases spreading over relatively broad band is suppressed. It is pointed out that the periodic frequency characteristic of a stage processing decimated signal causes decrease of attenuation in the stopband of the DSM, and an IIR section with a low decimation rate is employed as the first stage. A DSM the amplitude characteristic of which falls into the spectrum mask for IEEE 802.11 is designed as an example. Simulation results show that the designed DSM satisfies specification widely in not only the passband but also the stopband. It is confirmed that gradual decimation approach or use of a non-decimated section for the first stage is effective.