Question

Why do not we take the channel-length modulation and body-effect into consideration in Figure b,c,d? Why do we take the channel-length modulation and body-effect into consideration in Figure a? Why do we just take body-effect without the channel-length modulation into consideration in Figure e? What‘s more, in Figure e, when the Vx surpasses the gate-source voltage, is there the drain current in the M1?

2.5. Sketch Ix and the transconductance of the transistor as a function of Vy for each circuit in Fig. 2.47 as Vx varies from 0 to Vpp. In part (a), assume that Vy varies from 0 to 1.5 V. VOD Ix 4M +1.9VM +1V.M Vx Forx Ix Vx +1 V 1.9 V (a) (b) +1.5 V +1V1M +1.9v M1 +1.9VE +1VOO Vx + (d) (e)

Answer 1

For fig b,c,d substrate potential i.e potential of the bulk is not changing wrt source potential. I.e Vsb = constant. So it will not suffer from body effect. For channel length modulation to take place Vds should change but in fig b,c,d Drain potential is constant wrt source potential, so channel length modulation will not take place.

In fig a source potential is not fixed and its varying wrt bulk potential and drain potential so both body effect and channel length modulation will take place.

In fig e. Drain to source voltage is constant so channel length modulation will not take place. But substrate i.e bulk potential is varying wrt source potential so body effect will take place.

In fig e. As vx will increase it will lead to increase in threshold voltage Vth beyond vgs. So there will not be any conduction and no current beyond 1.9V.

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