A High Linearity and Low Noise Anti-Aliasing Filter for ADCs

This article designs a 2.5V low-pass filter with adjustable cutoff frequency, which has high linearity and high output signal to noise ratio. The filter uses switches to adjust the size of the capacitor, thereby changing the cut-off frequency. Compared with common cascode structure, the input stage uses a cross-coupling structure to improve linearity, and the output uses a current mirror mode common source amplifier to improve drive capability. The cut-off frequency is adjustable at 19MHz and 38MHz. The THD is -73dB and input reference noise is $8.95{\text{nV}}/\sqrt {{\text{Hz}}} $. This result can well meet the needs of the ADC.