cascode_biasing

cascode_biasing - cascode_biasing.mcd 9/1/2009 High-Swing...

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cascode_biasing.mcd 9/1/2009 High - Swing Cascode Biasing M4 M2 M1 I S X B A I S Y M3 Assume M1, M2, M4 are in saturation, and M3 in triode region. Vds1 is set to slightly above Vov1 by controlling Vds3 (sizing M3). Also assume square-law behavior and ignore CLM effect. M1 -->    Cox (W1/L1), Vov1 = Vgs1 - Vth1 M2, M4 -->  , Vov2 M3 -->  n, Vov3 Sizing : KVL : V gs2 V ds1 V gs4 V ds3 = V gs3 = The goal is to establish the gate voltages of M1 and M2 properly. I s 1 2 1 V ov1 2 = 1 2 2 V ov2 2 = n V ov3 V ds3 1 2 V ds3 2 = If M2 and M4 are matched devices of the same size, Vgs2 = Vgs4, and we have, V ds1 V ds3 = Also, V ds3 V gs4 V gs3 = So, V ov3 V ov4 V th4 V ds3 V th3 = V ov2 V ds1  V th = where, Vth is the threshold voltage difference between the cascode (M4) and bottom device (M3) So, 1 n 1 2 V ov1 V ds1 V th
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