AN1798

Principle of operation

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Principle of operation

Sigma-Delta converters, known also as oversampling converters, sample the input signal

many times for each output sample with a frequency rate much greater than the Nyquist

frequency (twice the input bandwidth). A Sigma-Delta converter consists of two blocks, the

first is the Sigma-Delta modulator which produces the bit stream to the second part which

consists of a digital filter and decimator.

Figure 1.

A Sigma-Delta converter block diagram

The STR71x ADC is a Sigma-Delta converter which composed of a second-order Sigma-

Delta modulator followed by a sinc3 digital filter and decimator.

ADC

DAC

Digital filter

and Decimator

Integrator

+

-

N bits of DATA

N bits

N bits

Vin

Σ