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I'm very much confused with the ADC terminology. I know what a differential amplifier is. And a differential amplifier can take a single-ended(unipolar) source as an input. It can of course better take bipolar inputs. There is also single-ended input amplifier where one end of the differential input is connected to the analog ground. This can only work with unipolar source.

But when it comes to datasheets of the ADCs, what does the following terminology mean?:

-Differential input channel ADCs

-Fully differential input channel ADCs

-Pseudo differential input channel ADCs

-Single ended ADCs

Is the above category about the source types(unipolar or bipolar), or is it about type of the amplifier itself?

For example if you go to this site: http://www.analog.com/en/products/analog-to-digital-converters/precision-adc-20msps/single-channel-ad-converters.html

There is a section called "Input types".

Edit:

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    \$\begingroup\$ First result on Google: maximintegrated.com/en/app-notes/index.mvp/id/1108 \$\endgroup\$ – Eugene Sh. Mar 28 '18 at 18:29
  • \$\begingroup\$ Yes I know the difference. But in this case is it used for the source type or the amplifier type? \$\endgroup\$ – atmnt Mar 28 '18 at 18:30
  • \$\begingroup\$ So if it is about the ADC inputs not the source terminals, does that mean I can use a diff ended ADC to sample a unipolar source? \$\endgroup\$ – atmnt Mar 28 '18 at 18:31
  • \$\begingroup\$ @EugeneSh. Im not asking the difference between single ended amplifier and diff ended. When they say single ended input are they talking about the ADC itself or the source to be coupled? \$\endgroup\$ – atmnt Mar 28 '18 at 18:33
  • \$\begingroup\$ Look at this one: ti.com/product/ADS8517 which confuses me more. It says "bipolar" when it talks about the inputs. If the inputs are about ADC internals not the source, what the heck is this then? There is nothing called bipolar input amplifier but source only can be called like that. Does anyone get where Im stuck? \$\endgroup\$ – atmnt Mar 28 '18 at 18:55
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Is the above category about the source types(unipolar or bipolar), or is it about type of the amplifier itself?

You are confusing input types with power supply types. An ADC can have either single-ended or differential inputs. Its power supply can be unipolar (ground with a single + power feed), or bipolar supply with something like +/- 5 volts.

  1. In terms of compatibility (ideally) you want the power source for the ADC to match the signal power source, unipolar or bipolar. This way a unipolar ADC is not likely to get a input voltage more negative than ground. If so then the input has to be scaled or clamped so it does not go negative. Most MPU's have unipolar ADC inputs so some method is needed to insure the ADC only sees voltages within its range of operation. It can have differential inputs but with a single-ended source the (-) input is connected to signal ground or the (-) output of a differential source.

  2. Bipolar ADC's are normally standalone types with 12 to 24 bit resolution and may or may not have differential inputs. But the ADC input voltage can go negative close to the negative supply rail. It may have a parallel or SPI port to communicate with a MPU. The cost are higher and much more detail to digital noise isolation is mandatory for these ADC's, which may have very high sample rates.

  3. Due to their lower cost most ADC's have unipolar power supplies as low as 3.3 volts, with a range of 0 to 3.3 volts. If in a MPU it normally had 10 bits of resolution, but some offer 12 bits of resolution with a single pair of differential inputs. As long as the source stays within the ADC's specified range then there are no damage or ADC reading error issues.

  4. In some cases manufactures specify a maximum series resistor value to limit current if a over or under voltage condition could happen, usually 1 K to 10 K maximum to avoid errors due to the internal sample/hold capacitor needing a minimum source impedance to charge up quickly during sample time.

  5. These resistors can be used with low-leakage diodes (not Zener or TVS diodes) to the power/ground rails or dedicated voltage clamps to limit the amount of over/under voltage possible.

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    \$\begingroup\$ Somehow a duplicate answer was created. I corrected the problem myself. I deleted the answer that was incomplete. Someone tried to edit my answer at the same time as I was. Give me some time to do my own edits. I do many reviews of an answer before I am satisfied with it. \$\endgroup\$ – Sparky256 Mar 28 '18 at 20:18
  • \$\begingroup\$ 1-) I made a tree after I read your answer and edited my question. Is this tree correct?: i.stack.imgur.com/5P69M.png (excluding pseudo-diff thing) . 2-) Imagine in case X, I use a "bipolar ADC which is designed as diff ended input" for reading a single-ended source. And in case Y, for the same single-ended source this time I use a "bipolar ADC which is designed as single ended input". Is case X better than case Y in terms of noise rejection? \$\endgroup\$ – atmnt Mar 29 '18 at 1:23
  • \$\begingroup\$ If both signal source and ADC are differential then you have the best common mode noise rejection, both option X or Y will work if you keep digital noise away from analog traces and use plenty of bypass capacitors. Most of what is on the market is single-ended source to single input ADC. The exception is professional audio/video gear and $250,000 USD mixing boards. Keep the grounds wide and power traces well filtered or both X and Y can have noise. Do NOT have digital grounds tied into analog grounds except at main power connector. \$\endgroup\$ – Sparky256 Mar 29 '18 at 1:32
  • \$\begingroup\$ But in data acquisition devices I guess most of the time the source is two wire single-ended(with a range ±5V for example) and the ADC is bipolar. That's why I asked. In that case I guess if the line is balanced enough case X is better than case Y for common mode voltages is that correct? \$\endgroup\$ – atmnt Mar 29 '18 at 1:42
  • \$\begingroup\$ Yes, when you have the option use option X, so you can choose your common reference in spite of various inputs. However most MPU's with ADC built in are 10 bit single ended, as in low cost. \$\endgroup\$ – Sparky256 Mar 29 '18 at 1:51

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