What is a sigma-delta analog-to-digital converter (ΣΔ ADC)?

The basic principle behind a sigma-delta ADC involves oversampling the analog input signal at a much higher frequency than the desired sampling rate and then using a feedback loop to modulate the output of a one-bit digital-to-analog converter (DAC). The modulated output is compared to the original analog signal, and the difference (error) is fed back to the DAC. This feedback loop effectively shapes the quantization noise, pushing most of it into higher frequencies. As a result, the overall noise power is spread out across a wider frequency range, and the effective number of bits (ENOB) of the ADC is increased, improving the resolution.

Sigma-delta ADCs are especially useful for applications where high resolution and noise performance are critical, such as audio applications, instrumentation, sensor interfaces, and telecommunications. They are often used in scenarios where the accuracy of the conversion is more important than the speed of the conversion.

The term "sigma-delta" comes from the Greek letters sigma (Σ) and delta (Δ), which are used to represent summation and difference, respectively, reflecting the mathematical operations involved in the modulation and demodulation processes of this conversion technique.

In summary, a sigma-delta ADC is a specialized type of analog-to-digital converter that leverages oversampling and feedback to achieve high-resolution conversions with improved noise performance, making it well-suited for applications demanding accurate signal representation.