1.1 Test and Measurement Methodology

The test methodology and electrical characteristics are based on a linear ramp histogram. For the 12-bit ADC, the ideal transfer function is defined as:

$f l o o r (\frac{V I N}{V D D} \times 4096)$

Each ADC count corresponds to 1/4096 of the input range.

When AV_DD is 3.3V nominal, the input range is 0V to 3.3V.

One ideal ADC count corresponds to a step size of $\frac{3.3 V}{4096} = 0.805 m V$ .

Figure 1-1illustrates the ideal transfer function. The floor() in the ideal transfer function yields an output code of 0 from 0V to one step size of the analog input. The maximum output code of 4095 corresponds to an analog input from AV_DD minus the step size to AV_DD.

Figure 1-1. Ideal Transfer Function

The linear ramp histogram method uses bins corresponding to each output code. Additional bins above and below the limits are included to account for errors. The two bins representing the ends of the actual transfer function are not included in the calculations. The lower-end bin can represent an offset error. An example of a histogram is shown in Figure 1-2. The number of hits in each bin is measured and compared to the ideal number of hits. The ratio of hits in each bin is then used to map the transfer function. Units for all specifications are in LSB.

Figure 1-2. Histogram