Hi,
Basic idea of chopping is upconverting signal to the odd harmonics of chopping frequency. However, due to the finite bandwidth of the amplier, some unwanted spurs emerge at even harmonics of the chopper frequency. You should filter them out. One good referance paper about noise suppression of these circuits is the Enz's famous paper which is named as "Circuit Techniques for Reducing the Effects of Op-Amp Imperfections: Autozeroing, Correlated Double Sampling, and Chopper Stabilization". You can find it in IEEE Xplore.