Quantization-Limited SNR on a 12-bit Multi-ADC Pipeline

Built a measurement system for digitising analog signals using a Raspberry Pi 3B with external MCP3201 12-bit ADCs and an op-amp low-pass filter front end. The system was evaluated through frequency-domain analysis, time-series inspection, and signal-to-noise ratio (SNR) calculations.

Verification confirmed correct waveform and amplitude reproduction, but identified a systematic DC offset visible in every FFT. Measured SNR at 1 kHz, 2 kHz, and 10 kHz was 55.22, 55.14, and 55.18 dB respectively, essentially flat across frequency, but ~19 dB below the 74 dB ideal-quantisation bound for a 12-bit converter.

The gap is consistent with quantisation noise in non-full-scale regions, power-supply interference, a lower-than-designed actual cutoff in the analog low-pass filter, and reference-voltage instability. Improvements identified for a follow-up: better EMI shielding, a low-noise reference, a more precise filter implementation, and post-hoc calibration of the systematic offset.