Amplifier with 2µV Standard Deviation Offset and 37nV/√Hz Input Noise Density

A key limit of the chopper stabilized technique is that the low-frequency noise after being shifted up to the chopping frequency is only partially removed by fil-tering. The auto-zero method does not suffer this limit, but the aliasing of the broadband input noise spectrum imposes the use of large sampling capaci-tances that, in turn, increase the bias current. The chopper method is the opti-mal approach for micro-power applications. This design uses a chopper, but avoids the chopper ripple at fs by combining input chopping with correlated double sampling (CDS) at the output of the first stage of the amplifier. Figure 4.2.1 shows the block diagram. The chopped input signal, added to offset and 1/f noise, is amplified by the first stage. Assuming that offset and 1/f noise do not saturate the amplifier, their contribution is removed by AC coupling, while the signal is detected by the correlated double sampling method. During one phase, two of the four Ccds capacitors are charged to the differential outputs and, during the complementary phase, they are con