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ADC10040 Input Range Select

Mike Enns
Prodigy 20 points

I find the description of the IRS pin confusing.  While the pin description indicates it has 3 states, tied high, tied low or open, several graphs plot a value, IRS, that varies continuously between  1V and 2V.  Is this the same IRS?

If so, the graphs indicate the performance improves by more than 3 db in some cases as the input range increases.  This implies that I am actually worse off by narrowing the range.  It makes no sense to me. Who would ever use the pin?

Here is the question.  We are looking for an easy way to add some gain.  Do I actually improve S/N by choosing a narrower range? The graphs imply that I would be better off just using the wide range.

  • 0
    TI__Expert 4340 points

    Mike,

    Yes, the plots of XXX vs. IRS are a little deceiving because they show a continuum of values on the X-axis. Regarless, IRS can be set in only 3 different states which achieve a input full scale range of 1.0, 1.5, and 2.0 Vpp respectively. The plots of XXX vs. IRS actually only have 3 data points which correspond to these 3 states. (the curvature of the lines indicates that there was some smoothing used in the plots, but there are still only 3 data points).

    The IRS function changes the input full scale range, but it is used to trade off noise performance for distortion performance. At the highest IRS setting (2.0Vpp) the noise (SNR) is optimized at the cost of dictortion (THD and SFDR). At the lowest IRS setting (1.0Vpp) the distortion is optimized at the cost of noise performance.

    Regards, Josh

  • 0 in reply to Joshua Carnes
    Prodigy 20 points

    Josh

    Thanks for the reply.  I see a marginal improvement in THD.  So, for my application, this is not where I should be looking for increased gain.

    Mike