How do chopper-stabilized amplifiers work and what are the design challenges?

Chopper amplifiers modulate the input signal to higher frequency, amplify it (where 1/f noise and offset are negligible), then demodulate back. The DC offset and 1/f noise of the amplifier are modulated to chopping frequency and filtered out. Result: microvolt-level offset, sub-nV/sqrt(Hz) noise at DC. Design challenges: Charge injection from chopping switches creates residual offset, Intermodulation of signals near chopping frequency, Settling time requirements during chopping transients, Input impedance modulation at chopping frequency, and High-frequency noise folding to baseband. Solutions include nested chopping, auto-zeroing combined with chopping, and careful switch design with dummy transistors.