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Delta-sigma (ΔΣ; or sigma-delta, ΣΔ) modulation is an oversampling method for encoding signals into low bit depth digital signals at a very high sample-frequency as part of the process of delta-sigma analog-to-digital converters (ADCs) and digital-to-analog converters (DACs).
A delta-sigma ADC (also known as a sigma-delta ADC) is based on a negative feedback loop with an analog filter and low resolution (often 1 bit) but high sampling rate ADC and DAC. The feedback loop continuously corrects accumulated quantization errors and performs noise shaping : quantization noise is reduced in the low frequencies of interest ...
English: This is a block diagram of a simplified Delta Sigma ADC and is my own work drawn using "Inkscape" a free svg editor. It was drawn to illustrate a description of the functioning of the so-called Delta Sigma ADC which appears in the overall article on Delta Sigma modulation.
In delta modulation, the transmitted data are reduced to a 1-bit data stream representing either up (↗) or down (↘). Its main features are: The analog signal is approximated with a series of segments. Each segment of the approximated signal is compared to the preceding bits and the successive bits are determined by this comparison.
Digital-to-analog conversion can degrade a signal, so a DAC should be specified that has insignificant errors in terms of the application. DACs are commonly used in music players to convert digital data streams into analog audio signals. They are also used in televisions and mobile phones to convert digital video data into analog video signals ...
Certain kinds of ADCs known as delta-sigma converters produce disproportionately more quantization noise at higher frequencies. By running these converters at some multiple of the target sampling rate, and low-pass filtering the oversampled signal down to half the target sampling rate, a final result with less noise (over the entire band of the ...
Sinc N filters are commonly used with delta-sigma modulation ADCs just prior to downsampling to the desired output data rate (ODR) of . A sinc N filter's frequency response will lie under a –20·N dB per decade envelope, so higher orders have steeper roll off for cutting out more high frequency noise, but will also have a lower -3 dB frequency .
This results in a broadband dynamic range of only 7.78 dB, but it is not consistent among frequency bands, and in the lowest frequencies (the audible range) the dynamic range is much greater — over 100 dB. Noise shaping is inherently built into the delta-sigma modulators. The 1-bit converter is the basis of the DSD format by Sony.