114.1(Operation as Vps is increased The induced channel acguires a tapered shape> Channel resistance increases as Vps is increased.> Drain current is controlled by both of the two voltages.+十UGSUDS1n-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. 4.1 Operation as vDS is increased B
124.1Channel pinched offWhenVsp=V,orVes-Vps=Vt,thechannelispinched offInversionlayeralmostdisappearedatthedrainpointUDS≥UGSVpsDrainChannelSourceUOs2025/11/27
2025/11/27 12 ⚫ When VGD = Vt or VGS - VDS = Vt , the channel is pinched off ➢ Inversion layer almost disappeared at the drain point ➢ Drain current does not disappeared! 4.1 Channel pinched off
134.1Drain current @ pinch off.Theelectronspassthroughthepinchoff areaat veryhighspeed soas the current continuity holds,similartothe waterflow at the Yangtze GorgesSourceDrainPinched-offchanneUGSToSsatDSsa2025/11/27
2025/11/27 13 4.1 Drain current @ 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
144.1Drain current @ pinch offDraincurrentissaturatedandonlycontrolledby the VGsiDATriodeSaturationUDS≥UGS-V,UDS<UGS-VCurve bends becauseCurrent saturates because-ththe channel resistancechannel is pinched off at theincreaseswithpsdrain end and wps no longeraffecis the channelAlmosta straight linewith slope proportionalto (UGS-V)UGS>V=UGS-V,0UpsUDSsa2025/11/27
2025/11/27 14 ⚫ Drain current is saturated and only controlled by the vGS 4.1 Drain current @ pinch off
154.1Drain current controlled by VssVcs creates the channel.·Increasing Vgs will increasetheconductance of the channel.·At saturation region only the Vcs controlsthe drain current.·Atsubthreshold region,drain currenthasthe exponential relationship with Vcs2025/11/27
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 4.1 Drain current controlled by vGS