Analysis of 1/ƒ2 and 1/ƒ3 noise in the high-pass chopper amplifier with a high-impedance source

Chopper stabilization is the most widely used circuit technique to reduce the influence of the flicker noise in an amplifier. Recently, observation of /f² input-referred noise in the chopper amplifier with a high-impedance input source was reported. However, the mechanism of this /f² phenomenon has not been completely analyzed. This paper provides the complete analysis of the noise influence generated by a chopper switch. The analysis suggests that the noise current of a chopper switch is directly fed to the output when the impedance of the input signal source is high. Then, the thermal noise of the chopper switch is reflected to the input showing /f² characteristic while the flicker noise of the chopper switch is reflected to the input showing /f³ characteristic. This analysis has been verified with the simulation and measurement results.