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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

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Parents
  • The first stage integrator is inherently inverting, and thus the output (Vint) would start at zero and slope negative.  The comparator will never trip.  You could add another inversion stage (after the integrator).  Inverting the Vref would also work if you had negative supplies in the system.

Reply
  • The first stage integrator is inherently inverting, and thus the output (Vint) would start at zero and slope negative.  The comparator will never trip.  You could add another inversion stage (after the integrator).  Inverting the Vref would also work if you had negative supplies in the system.

Children
    •  Analog Employees 
    in reply to TimW

    Hi  , thanks for your reply! Yes, there is indeed an inverting problem in the integrator. But there is also a fundamental mistake both in the text and in the circuit: as it is the structure cannot operate as an ADC! 

    •  Analog Employees 
    in reply to KCC

    In order for it to function as an ADC, there needs to be circuitry added to count the elapsed time to trip the comparator.

    •  Analog Employees 
    in reply to TimW

    Yes  , you might have said it in your very first message: in order for the integrator working in a such way the integration time is proportional to Vin, one must swap the position of Vref and Vin in the front end circuit.