Successive Approximation Register (SAR) ADCs A Successive Approximation Register (SAR) ADC is a discrete-time analog-to-digital converter (ADC) that utilizes...
A Successive Approximation Register (SAR) ADC is a discrete-time analog-to-digital converter (ADC) that utilizes a sequence of weighted sums to achieve high conversion accuracy. It consists of the following key components:
Reference input: This pin provides a reference voltage that determines the full-scale range of the ADC.
Input sampling pins: These pins sample the analog input signal at regular intervals.
Weighting resistors: These resistors determine the weight assigned to each sample.
Binary encoder: This circuit converts the weighted sums into a digital code.
Conversion clock: This signal controls the sampling process and determines the update rate of the ADC.
The SAR ADC operates by repeatedly reading the analog input, multiplying it by its weight, and adding the results. The weighted sums are then accumulated in a binary counter, which is subsequently converted into a digital code by a digital-to-binary converter.
Advantages of SAR ADCs:
High accuracy: The SAR ADC achieves high conversion accuracy due to its ability to perform multiple weighted sums in a single clock cycle.
Low sampling jitter: The continuous sample and hold operation eliminates sampling jitter, resulting in improved conversion accuracy.
Wide input voltage range: The SAR ADC can be used with a wide range of analog input voltages, making it suitable for various applications.
Disadvantages of SAR ADCs:
Complex design: The SAR ADC requires more complex circuitry compared to other ADCs.
Finite resolution: The SAR ADC has a finite resolution, determined by the weight values used in the weighting resistors.
Non-linearity: The nonlinear relationship between the analog input and digital output can introduce non-linearity in the conversion process.
Example:
Imagine an SAR ADC with 8 weights, each corresponding to a different binary digit. The reference voltage would be set to a voltage corresponding to the full-scale range of the ADC. The analog input would be sampled at regular intervals, and the weights would determine how much each sample weight contributes to the final digital output. By combining these weighted sums, the SAR ADC would be able to achieve high conversion accuracy