11Operation as Vps is increased> The induced channel acquires a tapered shape> Channel resistance increases as Vps is increased.> Drain current is controlled by both of the two voltages.1十UGS丰UDS三Pn-channelp-typesubstrateOB2025/11/27
2025/11/27 11 ➢ The induced channel acquires a tapered shape. ➢ Channel resistance increases as vDS is increased. ➢ Drain current is controlled by both of the two voltages. Operation as vDS is increased B
12Channelpinchedoff When VGp = V, or VGs - VDs = V, the channel ispinched offInversion layer disappeared at the drain pointDrain current does not disappeared!UDS≥UGS-UpsDrainChannelSourceRUps2025/11/27
2025/11/27 12 ⚫ When VGD = Vt or VGS - VDS = Vt , the channel is pinched off ➢ Inversion layer disappeared at the drain point ➢ Drain current does not disappeared! Channel pinched off
13Drain currentunder pinchoff.The electrons pass throughthepinchoff areaatveryhighspeedsoasthe current continuity holds,similartothe waterflow at the Yangtze GorgesSourceDrainPinched-offchannelUGSUSsupssaT2025/11/27
2025/11/27 13 Drain current under pinch off • The electrons pass through the pinch off area at very high speed so as the current continuity holds, similar to the water flow at the Yangtze Gorges Pinched-off channel
14Drain currentunder pinch offDrain current is saturated and only controlled bythe VGsiDATriodeSaturationUDS≥UGS-V,UDS<UGS-V.Curve bendsbecauseCurrent saturates because thethe channel resistancechannel is pinched off at theincreaseswithpsdrain end and wps no longeraffecis the channelAlmost a straight linewith slope proportionalto (UGS-V)GSV=UGS-V,0UpSsatUDs2025/11/27
2025/11/27 14 ⚫ Drain current is saturated and only controlled by the vGS Drain current under pinch off
15Drain current controlled by VGSVs creates the channel. Increasing 'cs will increase the conductance ofthe channel. At saturation region only the Vcs controls thedrain current.At subthreshold region, drain current has theexponential relationship with VGs2025/11/27
2025/11/27 15 ⚫ vGS creates the channel. ⚫ Increasing vGS will increase the conductance of the channel. ⚫ At saturation region only the vGS controls the drain current. ⚫ At subthreshold region, drain current has the exponential relationship with vGS Drain current controlled by vGS