The Google search term "analog-to-digital converter selection" has produced thousands of search results, proving that this task remains challenging for many people involved in designing sensing solutions. After all, there are a large number of analog-to-digital converter (ADC) solutions from simple 10-bit ADCs integrated in 8-bit microcontrollers (MCUs) to ADCs that can resolve at GHz rates.
Unless you are designing a dedicated sensing front end, you are likely looking for an integrated ADC that delivers high quality performance without compromising energy or operational flexibility. In this article, I have listed a few parameters that can help you narrow down the search range of your ADC. You may also want to refer to other parameters depending on the specific needs of your application.
Resolution. Perhaps the most discussed ADC parameter, there are many problems with regard to whether the number of bits that the ADC can resolve is the most important measurement of its accuracy. An easy way to look at this is by examining the actions your application takes after the ADC transitions. For example, is it a relative measurement to measure whether a temperature change has occurred? If so, a 10-bit or 12-bit ADC is sufficient because this is a true-false-no problem. On the other hand, consider products such as electric meters. In this application, analog to digital conversion requires high precision. The accuracy of load current measurements can mean differences in energy usage and utility billing differences. This type of application typically uses >16-bit delta-sigma ADCs to ensure high quality conversion results.
Sampling Rate. The sampling rate of the ADC is directly dependent on the frequency of the input. Thanks to our scholar friend Nyquist, you know that the ADC must sample with > 2 times the input signal (F sample ≥ 2x F input) and you know that there is a minimum required sample rate. For example, an input of 100 kHz requires sampling at a frequency of ≥200 kHz. However, the sampling rate specified in the data sheet covers only the true "sampling + conversion" clock - without taking into account any setup time of the ADC, post-processing conversion results for decision making or off-chip moving data. These factors are equally important because they allow you to calculate the period and duty cycle of the ADC conversion to calculate the remaining margin for post processing.
For example, an ADC sample of 1 MSPS will acquire 1,000 16-bit samples in 1 ms. If you use the double buffering method to capture ADC samples, then you know that you have ≤1ms of time to process the data buffer, take action based on the results, and possibly move the data before the next data set is ready for processing.
Reference selection. An important criterion when evaluating an integrated ADC is the availability of an internal precision reference source. In some cases, the ability to set multiple reference voltage ranges ensures flexibility in resolving the different input ranges of the ADC.
The scope of work. Many ADCs operate within a limited portion of the total supply voltage range available for the device. It is important to measure the needs of your application in this area. For example, in battery-powered applications, it may be necessary to drop to the lowest supply voltage range (1.8V is typical for MCUs, although some of TI's SimpleLinkTM MSP432P4 family can operate at 1.72V) to ensure reliable conversion Until the device is turned off.
Input channel. The number of input channels is not just the number of externally available pins that can be used to connect to an analog input. When choosing an ADC for a set of inputs that need to be sorted, it is also important to consider the flexibility of the channel configuration. The availability of optional reference sources, dedicated interrupt and conversion registers, and differential input and configurable data formats is important to ensure efficient setup of the ADC configuration, enabling customizable settings and preventing wasted cycles in setup.
As I mentioned at the beginning of this article, the actual list of ADC selection criteria may be longer depending on what the application is trying to sense. You can evaluate the MSP432P4 high-performance ADC with up to 16-bit accuracy by purchasing the MSP432P4 LaunchPadTM Development Kit and quickly obtaining a tutorial on using precision ADCs through our SimpleLink Academy training portal.
For an in-depth look at the topics of ADC selection and to see how TI's MSP432P4 high-precision ADC compares to existing ADCs on the market, check out the chart in Figure 1 below and see our application report, which provides useful tips for interpretation. ADC data table parameters.
Figure 1: Performance of the MSP432 16-bit precision ADC compared to competing products
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