digital compensation of dynamic acquisition errors at the front-end of ...

8 Chapter 2: Nonlinearity at the ADC’s Front-End
characterize the performance of the converter [12], [13]. Several static and dynamic
metrics have been defined for this purpose, and depending on the particular
application, some of these metrics become more or less relevant.
Figure 2.1: Block diagram of an analog-to-digital converter, including sampling and
quantization.
One of the main metrics defining the performance of an ADC is its linearity,
which is an important factor in high-resolution ADCs used in the receiver
architectures discussed in Chapter 1. Any nonlinearity in the ADC path of these
receiver architectures distorts the desired signal and spreads it in frequency as shown
in Figure 2.2. This distortion corrupts the information in the received signal and
affects the accuracy of the system. It is therefore important to achieve sufficient
linearity in the ADC not to exceed the error tolerance of the system.
In order to characterize the linearity of the ADC, several metrics are defined such
as: Integral Nonlinearity (INL), Differential Nonlinearity (DNL) and Spurious Free
Dynamic Range (SFDR). INL and DNL are measured from the transfer function of the
ADC and define its static linearity (or the ADCs linearity at low input frequencies).
DNL is defined as the difference between the actual step width and the ideal step size
of 1 LSB in the transfer function of the ADC. INL is defined as the deviation of the
actual transfer function from the straight line passed through the end points of the
transfer function. Figure 2.3 illustrates the definition for these terms on the static