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CMOS OTA with low gm

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an_82

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Hi every body,

I designed a new CMOS OTA which has high linearity as a voltage-to-current convertor. Also I utilized a technique in which "Iabc" has a direct proportion to "gm", i.e : Iabc=Kgm, where K consists of W/L of input transistors and some other constant parameters. By the way all of the transistors are in saturation region not weak inversion.

However the problem is that its "gm" (total gm of OTA) is low (20-30u). How can I increase that?
If I enhance the output impedance does "gm" increase ?
 

Dominik Przyborowski

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The transconductance of your OTA is \[K \cdot {g_m} \], where K is the ratio of loaded current mirrors and \[g_m\] it's a transconductance of input trransistors. In strong inversion \[g_m \sim \sqrt{I_d}\] but saturate in weak inversion (look for the gm/Id relationship). Choose W/L ratio of your input pair to work in moderate inversion (Vgs slightly higher than Vth) and increase your bias current or current mirror ratio.
 

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