sigma-delta ADC 基础1

The ΔΣ ADC is constructed from a ΔΣ modulator and a digital filter. The modulator

converts the analog input into a digital bit stream, while the digital filter translates the bit

stream into a data word that represents the magnitude of the analog input.

Let’s take a look at how the modulator works, starting with a very basic analysis of a

first-order, ΔΣ modulator topology, as shown in Figure 1.

Figure 1: Delta-sigma modulator internal block diagram

The modulator runs off of the modulator clock, which determines the sampling interval of

the input. The modulation loop begins by integrating the difference between the input

completes a full cycle and generates a new output.

As the modulator clock continues to run, each modulator clock pulse will generate

another modulator output pulse. The resulting output bit stream becomes a

representation of the input voltage, proportional to the reference voltage. Figure 2 shows

an input sine wave and the resulting modulator output bit stream, assuming a 1-V

reference.