ADC feature explanations

Question

I am looking for an ADC for my project and there are a few features that I don't quite get. On TIs product selector. The default filters includes INL, SNR, SFDR. I assume they are important since but some of them have value some dont, so I assume its ADC-spefic (or maybe they did not just write it) not all ADC have them, being just initials makes it harder to search.

Here are others on which I need some advice:

Programable Gain Amplifier(PGA) - Assuming same sample speed, Which would be better a 16-bit ADC using internal gain or a 24-bit (or 32-bit) ADC that is using no gain. Gain also amplifies the noise but assuming the isolation is perfect, wouldn't the 16-bit with a gain of 2 or more be better to the 32-bit using no gain? Of course there is gain drift but at low gains it's not much.

Simultaneous or Multiplexed Sampling - Although this one is self explanatory, Isn't simultaneous sampling (for multiple channels) always better? Are there other notable reason why to choose multiplexed over simultaneous?

Here are 2 ADC that have very peculiar features about which I have no idea:

• AC excitation (ADS1261)
• 50/60Hz notch (ADS1243)

Those two interest me because what I plan to use my circuit is to read voltages from a current transducer so that I can get the current consumption of a mains line.

Also what are all these gold for? are there really applications for it? gold, more gold

Answer 1

Here is everything that i have gathered.

INL - Integral Non-Linearity

Basically, this is error of the reading of the ADC (and DAC) to the actual values. The value is calculated by:

 INL = Vreal - Vmeasured

Generally the lower this value is, the better. Higher pecision bit ADC suffers from high linearity reducing their Effective Number of Bits (ENOB), consult datasheet to know more about the specific adc. More info on INL here

SNR - Signal to Noise Ratio

It is the ratio of the signal to the noise.

The formula is signal divided by noise. From that formula we would generally want a high signal to noise ratio so that more of the signal can be seen and less of the noise. I do not know why they put this as a filter as this is an application specific measurement, different noise will hit your circuit thus the SNR will vary from application.

SFDR - Spurious Free Dynamic Range

Is the ratio of the fundamental signal to the strongest spurious signal in the output. radio receiver application, Im having trouble putting it into words but you can read more here

From what i understood you generally want a higher ratio, but again this is an application specific measurement as it uses noise in its equation, and noise is something that is application specific.

PGA

Try as much as possible to use the least/no gain as a gain amplifier instroduces aliasing and you would not want that, the higher your gain the higher the alias too.

Simultaneous or Multiplexed Sampling

As DKNguyen said multiplexed is best case but will slightly cost you, get it if your constraints allow you.

Notched Filter

A very narrow band stop. And a band stop at 50HZ/60Hz which is also our target working frequency, really not ideal for the application i want to use it with.

AC excitation

the system which is used for providing the necessary field current. Im not really sure how can this be used alongside an ADC. You ca read more about AC excitation here

Golds

Please refere to @Sephro Pefphany's answer

Answer 2

I don't think you want a mains frequency notch filter if you're trying to read mains frequency signals.

In answer to your final questions, those packages appear to be special high temperature packages rated for up to 210°C operation. This kind of thing is required for down-hole applications. That also accounts for the hefty (~$600 USD) pricetag for a part that's normally < $50.

They also specify the minimum lifespan as better than 1000 hours only (death due to electromigration).