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    Current Mirror OTA gain calculation

    Dear all,

    I designed a current mirror. Some papers such as http://www.imec.be/esscirc/essderc-e...ons/063_50.pdf said the DC gain is

    A0 = gm1 x B x ro3.

    I computed it with mine, but, in the simulation, the B factor doesn't seems to have any impact on the DC gain, only on the GBW. Not sure if there is a reason, my inputs transistors are working in subthreshold region.

    Any Idea, suggestions?

    Thank you...

    •   Alt4th October 2013, 17:42

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    Re: Current Mirror OTA gain calculation

    Quote Originally Posted by Fabien View Post
    A0 = gm1 x B x ro3.

    ... the B factor doesn't seems to have any impact on the DC gain, only on the GBW.

    Any Idea, suggestions?
    The DC gain ~ B * ro3

    Now read the 1st paragraph of point 2.3. of your a.m. paper!


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    •   Alt5th October 2013, 16:26

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    Re: Current Mirror OTA gain calculation

    OK, thank you for you answer. So the B factor doesn't have any impact as the ro will change with B...
    But, if the gain is boosted B times and the output resistor is reduced B times, it means the DC gain is gm1 x ro3, doen't it?
    If yes, the gm1 is 12.8µS (qID/nkT) and ro3 = 5.5MOhms... it gives only 70 so 37dB...



    •   Alt8th October 2013, 16:24

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    Re: Current Mirror OTA gain calculation

    Quote Originally Posted by Fabien View Post
    But, if the gain is boosted B times and the output resistor is reduced B times, it means the DC gain is gm1 x ro3, doen't it?
    Fabien: No! DC gain is gm1 x B x ro3 , as you stated yourself above!


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    Re: Current Mirror OTA gain calculation

    OK, so I probably made a mistake when I calculate ro3...
    For gm1, in subthreshold I've only this equation: gm1 = qId/nkT (from Martin's book)



    •   Alt8th October 2013, 21:50

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    Re: Current Mirror OTA gain calculation

    Quote Originally Posted by Fabien View Post
    OK, so I probably made a mistake when I calculate ro3...
    For gm1, in subthreshold I've only this equation: gm1 = qId/nkT (from Martin's book)
    This is quite ok, I think. The gain enhancement doesn't depend on B , but is based on the (1−k)*ID1 current shunting, see and study equns. (5) & (6) of item 2.3. of your a.m. paper thoroughly!



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