How does sigma delta work

The modulator outputs data to the digital filter at this rate, in turn the digital filter typically low- pass, with some decimation provides data at the output data rate ODR. Figure 3 illustrates this flow.

The output and feedback are coarsely quantized often only a single bit output as a high or low. The basic structure is implemented as an analog system for ADCs, where the quantizer is the block in which the sampling is accomplished.

Provided conditions exist for stability of the loop, the output is a coarse representation of the input. The digital filter takes the coarse output and reconstructs an accurate digital version of the analog input.

A ones density output in response to a sine wave input is illustrated in Figure 4. The rate of change of the modulator output from a low level to high level depends on the rate of change of the input. The rate of change of the output is following that of the input. Figure 4. Using a linear model to describe this single bit modulator Mod 1 the system is shown as a control system with negative feedback. The quantization noise is the difference between the input and the output of the quantizer. A low-pass filter follows the input delta node.

In Figure 5b, the quantization noise is described by the term N. Figure 5. H f is the function of the loop filter and it defines both the noise and signal transfer functions. H f is a low-pass filter function with very high gain at low frequencies within the bandwidth of interest and attenuation of higher frequency signals.

The loop filter can be implemented as a simple integrator or a cascade of integrators. The sigma-delta modulator loop typically runs at a much higher frequency than the final output rate of the digital filter. For example, a converter with a 2kHz output data rate may have a modulator loop frequency of over 2.

Enter an ADC reference voltage in the lower input field. Enter the voltage to be converted in the V IN field. Click the Next Step button to move the tutorial forward a step. At each step the diagram is updated to show the current output of each block.

To see the outputs at the previous step of the tutorial, click the Previous Step button. To advance the tutorial complete loops of the modulator, click the Next Loops button. The outputs from the comparator will be: 1, 0, 1, 1, 1, 0, 1, 1. This means 6 of the 8 outputs have been a 1; i.

The allowed input range is