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KCC's quizzes AQQ260 about a technical article correction

1. Quote of the week: "No man goes before his time - unless the boss leaves early" - Groucho Marx

             

2. New quiz AQQ260 about a technical article correction

One (external) reader has noticed a mistake or imprecision in an ADI technical article:

https://www.analog.com/en/resources/technical-articles/adc-architectures.html

 The “faulty” section is displayed here below (note the BU is checking this for a coming quick update):

Questions:

  1. What and where is the error or imprecision?
  2. How would you correct it?

Good luck! And try to be among the firsts!

Kuo-Chang

P.S. Don't hesitate to share those weekly quizzes in EZ to colleagues or friends!

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Parents
  • Hum, missing the negative sign?  Depends on the convention in the document, but the Vint should be proportional to minus Vin ( 180 degree pahse shift). Not sure about how Tint is defined though, since it appears only in the graph and not in the schema.

  • That's somehow true: there is a sign problem. But there is also an other more fundamental mistake... And that is present on both the text description and on the schematics!

Reply Children
  • Indeed, if Vin, constant, is doubled, Vout will reach saturation twice as fast, so Vin and the time, Tin, is thus inversely proportional to Vin, as long as the OPAMP are not in saturation, Simple simulation confirms it (not with ideal OPAMP since ideal OPAMP have no saturation limits).
    So kind of changing the proportion for its inverse, the only correction that I can see is to add the possibility that the OPAMP reaches saturation? Else, the graph and the numerical simulation both agree.

  • And if you want an ADC, for all I know, you need to exchange Vin and (-)Vref, and add a switch in parallel to the capacitor (to discharge it), among other things. (And some more.)

  • Yes! You get it  ! Congratulations! swapping Vin and Vref is the minimum and fundamental change to be done on the circuit in order to have it working as an ADC! Let's hope our BU will modify that article as soon as possible!