Transcription of Subthreshold Operation and gm/Id design - CppSim
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PerrottAnalysis and design of Analog Integrated CircuitsLecture 16 Subthreshold Operation and gm/IdDesignMichael H. PerrottApril 1, 2012 Copyright 2012 by Michael H. PerrottAll rights PerrottA Closer Look at Transconductance Assuming device is in strong inversion and in saturation:2 IdVgsId_op VVTHVgs_opVds > VM1 IdVgsNMOS gsdgm = Vgs IdVgs_opID= nCox2WL(Vgs VTH)2(1 + Vds) gm= Id Vgs nCoxWL(Vgs VTH) s2 nCoxWLId gm Idq2 nCoxW/L Id 2Id(Vgs VTH) PerrottUnity Gain Frequency for Current Gain, ft Under fairly general conditions, we calculate: ftis a key parameter for characterizing the achievable gain bandwidth product with circuits that use the device3|Id/Iin| PerrottCurrent Density as a Key Parameter Current density is defined as the ratio Id/W.
Transconductance in Subthreshold Region Assuming device is in subthreshold and in saturation: 12 Id Vgs Id_op Vds > 100mV M1 Id Vgs NMOS g s d gm = ΔV gs ΔId Vgs_op Vgs_op ⇒ gm = δId δVgs ≈ID0 W L eVgs/(nVt) 1 nVt = Id nVt Recall for strong inversion : gm ≈ 2Id (Vgs −VTH) ID ≈ID0 W L eVgs/(nVt) g m purely a function of I d!
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