Hello,

At the moment I am looking at the spec's of the AD7872 ADC.

I need to verify and measure some spec for our customer.

One of those spec is the INL.

Can you tell me how it is measured.

- Is the reference line between the endpoints( code 0x0000 - code 0x3FFF)

or between midscale (code 0x1FFF and endpoints(code 0x0000 and code 0x3FFF) to cerrect for for the offest error.

- Is the INL the result of the Endpoint or Bestfit line.

- Have you got a graph of the INL

Thanks in advance for handeling this question

Ronald Dekker

Engineer at Applicos

Hi Dexter,

Linearity is measured using the end point method. For this device running a signal either as a DC ramp or a Sine Wave through the ADC. Typically the input is slightly overranged, ensuring that all codes in the transfer function are exercised. By running a ramp or sine wave a histogram of codes for the full transfer function is taken, the analog input at each step of the ramp is known and measured along with the ADC output code for that particular analog input.

The DNL (no missing codes) specification is firstly derived - this is the maximum change in the output code when a 1LSB change in analog input voltage is applied to the ADC. By stepping the analog input through all points in the transfer function it can be determined if there are no missing codes.

From this data the INL can be derived - with INL error being the error between the ideal straight line transfer function and the actual ADC transfer function (given that you have an associated analog input with each ADC code output the maximum INL error can calculated).

I was not able to find a plot of the INL error for the AD7872 my apologies on this.