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TLV9001-Q1: TLV9001 input transition region

Part Number: TLV9001-Q1

Hi team,

Do we have any recommended application note for the rail to rail amplifier as TLV9001-Q1?

My customer is using it to sense AC voltage, the common mode input range is also varying with the AC voltage, so there could be some period which falls to the transition regions. According to d.s. the PSRR, CMRR etc spec will degrade but I dont understand the reason and how to evaluate the impact. Could you help explain or share with me some articles to read through to better understand it? Thank you

Thank you

Scarlett

  • Hey Scarlett,

    Below are the formulas for PSRR and CMRR

    CMRR = ΔCommon-mode / ΔVoffset

    PSRR = ΔPower Supply / ΔVoffset

    Your transition region is caused by having complimentary (PMOS and NMOS) input stage transistors. At the transition region, your PMOS input stage turns off and your NMOS input stage turns on. This can introduce a large voltage offset because the offset of your PMOS stage is not correlated to the matching of your NMOS stage. This is evident in the typical characteristic graphs, where many samples show their offset over common-mode voltage. Since this offset change is so large, we typically set it as close to one supply as possible to avoid having the transition region in the middle of your common-mode range. 

    As your input signal gets closer to your positive supply rail, you can see that the offset of the NMOS stage is not only uncorrelated, but has has a wider distribution.

    This degrades CMRR because your offset now changes more as your input common-mode changes, increasing the value in the denominator of the above formula.

    This degrades PSRR as you lower your supply with a fixed common-mode voltage, you move your transition region down until it crosses your common-mode voltage.

    You can see more information in the TI Precision Labs video on Input and output limitations.

    https://www.ti.com/video/4620557492001 

    Best,
    Jerry