You can consider the analog-to-digital converter as a closed box, as shown in Figure 5. But what is inside the box? That is exactly what we are going to explain now.

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Figure 5: Analog-to-digital converter.

There are several ways to build an ADC. We can divide ADC design into four main groups:

• Parallel design (also known as Flash ADC);
• Digital-to-Analog Converter-based design (e.g., ramp counter, successive approximation, tracking);
• Integrator-based design (e.g., single-slope, dual-slope);
• Sigma-delta design (also known as delta-sigma, 1-bit ADC or oversampling ADC).

Each one of these main groups can have several different implementations. We are going to talk about each one of these groups individually.