Delta-sigma (ΔΣ; or sigma-delta, ΣΔ) modulation is a digital signal processing, or DSP method for encoding analog signals into digital signals as found in an ADC. It is also used to transfer higher-resolution digital signals into lower-resolution digital signals as part of the process to convert digital signals into analog.
In a conventional ADC, an analog signal is integrated, or sampled, with a sampling frequency and subsequently quantized in a multi-level quantizer into a digital signal. This process introduces quantization error noise. The first step in a delta-sigma modulation is delta modulation. In delta modulation the change in the signal (its delta) is encoded, rather than the absolute value. The result is a stream of pulses, as opposed to a stream of numbers as is the case with PCM. In delta-sigma modulation, the accuracy of the modulation is improved by passing the digital output through a 1-bit DAC and adding (sigma) the resulting analog signal to the input signal, thereby reducing the error introduced by the delta-modulation.