How do you design a high-precision data acquisition system achieving 20-bit effective resolution?

Achieving 20-bit effective resolution requires: ultra-low noise analog front-end (chopper-stabilized or auto-zero amplifiers with nV/sqrt(Hz) noise density), precision voltage reference with low drift (<1 ppm/C), sigma-delta ADC with high oversampling ratio and digital decimation filtering, careful PCB layout (separate analog and digital planes, guard rings, proper decoupling), controlled environment (temperature stabilization or compensation), and calibration strategy (multi-point calibration with traceability). Address: power supply rejection (isolated clean supplies), EMI shielding, proper grounding topology, and input protection that doesn't degrade signal integrity. Verify with noise spectral analysis and Allan deviation measurements.