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This summing can be accomplished by means of a switched capacitor circuit which accumulates charge onto a capacitor summing node.Īn integrator then adds the output of this summing node to a value it has stored from the previous integration step.Ī comparator outputs a logic 1 if the integrator output is greater than or equal to zero volts and a logic 0 otherwise.Ī 1-bit DAC feeds the output of the comparator back to the summing node: +V REF for logic 1 and -V REF for logic 0. The input voltage V IN is first summed with the output of a feedback DAC.
More sophisticated parts may have multiple modulators and integrators however these tend to obscure the underlying sigma-delta principle.
The diagram inside the applet shows a basic first order sigma-delta modulator.