a sigma-delta ADC

The sigma-delta ADC reaches astonishing resolution — 20, 24 bits — by trading away speed and using a counterintuitive idea: instead of measuring the input precisely once, it measures it crudely but millions of times, then averages. It is like weighing a letter on a coarse scale by quickly tapping it on and off thousands of times and averaging the readings — each glance is rough, but the average is exquisitely fine. This makes it the champion for slow, precise jobs: weigh scales, temperature, audio, and bridge sensors.

It works by combining two tricks. First, oversampling: it samples far faster than Nyquist needs, often hundreds or thousands of times faster, which spreads the quantization noise over a huge band so only a sliver of it lands in your signal band. Second, noise shaping: a feedback loop with an integrator deliberately pushes the quantization noise UP in frequency, away from your low-frequency signal and toward the top of the band, where a digital filter then throws it away. The front end can be astonishingly simple — often just a 1-bit comparator — yet the heavy oversampling and shaping recover many true bits. A digital decimation filter averages the fast 1-bit stream down to a slow, high-resolution number.

Why this matters, and the honest tradeoff: this is how you get 24 bits of clean, low-noise measurement cheaply, and a bonus is that the heavy oversampling makes the analog anti-alias filter trivially gentle. The price is speed and latency. Because it must take many samples and run a digital filter to produce one output, a sigma-delta is slow — output rates of a few hertz to a few hundred kHz — and the filter introduces delay, making it a poor fit for fast, one-shot, or multiplexed measurements where SAR or flash shine. Use it when resolution and quiet matter more than speed.