AN4207

Basics of sigma-delta converters

Doc ID 023945 Rev 1

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Basics of sigma-delta converters

Sigma-delta converters, also known as oversampling converters, consist of two basic

circuits: a modulator and a digital filter (Figure 1). In the modulator, the input signal is added

to the negative feedback signal from the digital to analog converter (DAC). The signal’s

difference, after passing through the integrating circuit, reaches the input of the comparator

(1-bit ADC), where it is compared to the reference voltage (the comparator works as a 1-bit

quantizer). The input signal from the comparator (1-bit ADC) controls the 1-bit converter and

reaches the input of the digital filter, which decreases flowability and transforms the 1-bit

stream into 16-bit words. The used filter topology that ensures the low-pass stage is Sinc³.

Figure 1.

Block diagram of a sigma-delta analog to digital converter

1-bit ADC

1-bit DAC

Digital filter

&

Decimator

Vin

1-bit stream

MSv31135V1

16-bit data