Delta-sigma (ΔΣ; or sigma-delta, ΣΔ) modulation is a method for encoding analog signals into digital signals or higher-resolution digital signals into lower-resolution digital signals. The conversion is done using error feedback, where the difference between the two signals is measured and used to improve the conversion. The low-resolution signal typically changes more quickly than the high-resolution signal and it can be filtered to recover the high-resolution signal with little or no loss of fidelity. This technique has found increasing use in modern electronic components such as converters, frequency synthesizers, switched-mode power supplies and motor controllers.
Both analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) can employ delta-sigma modulation. A delta-sigma ADC first encodes an analog signal using delta-sigma modulation and then applies a digital filter to form a higher-resolution digital output. On the other hand, a delta-sigma DAC encodes a high-resolution digital input signal into a lower-resolution signal that is mapped to voltages and then smoothed with an analog filter. In both cases, the temporary use of a lower-resolution signal simplifies circuit design and improves efficiency.
The coarsely-quantized output of a delta-sigma modulator is occasionally used directly in signal processing or as a representation for signal storage. For example, the Super Audio CD (SACD) stores the output of a delta-sigma modulator directly on a disk.