Low Frequency Characteristics of JFETs Low Frequency Characteristics
- Slides: 8
Low Frequency Characteristics of JFETs Low Frequency Characteristics of Junction Field Effect Transistors Electronic Devices Laboratory mtinker@utdallas. edu CE/EE 3110
Low Frequency Characteristics of JFETs • Junction FET (JFET) one form of an FET transistor Ø Ø Voltage-variable depletion width used to control transistor operation Causes pinch-off and device saturation Exhibits both a linear and saturated I-V characteristic Small signal operation modeled by transconductance and shunt resistance in pinched-off mode of operation Electronic Devices Laboratory mtinker@utdallas. edu CE/EE 3110
Low Frequency Characteristics of JFETs Variation of depletion width across JFET channel (a) and current-voltage characteristics versus gate voltage (b). Electronic Devices Laboratory mtinker@utdallas. edu CE/EE 3110
Low Frequency Characteristics of JFETs 2 N 5485 n-channel JFET IDS-VDS characteristics (upper left), inputoutput characteristic (i. D(sat. ) vs v. GS) of a JFET (upper right), and small signal model of a JFET in pinched off mode of operation (bottom). Electronic Devices Laboratory mtinker@utdallas. edu CE/EE 3110
Low Frequency Characteristics of JFETs Measurements: 1) ID(Sat. ) = IDSS(1+VGS/VP)2 2) VP = -VGS + VDS(Sat. ) 3) gm = Δi. D/ΔνGS (νDS = const. ) 4) rd = ΔνDS/Δi. D (νGS = const. ) Experimental values for Vp, ID(Sat. ), gm, and rd and theoretical values for I D(Sat. ). Plot the IDS versus VDS characteristic and show pinch-off locus in the plot Plot both the experimental and theoretical curves for ID(Sat. ) versus νGS Determine gm and rd at νDS = 8 V Electronic Devices Laboratory mtinker@utdallas. edu CE/EE 3110
Low Frequency Characteristics of JFETs JFET IDS – VDS Curves Electronic Devices Laboratory mtinker@utdallas. edu CE/EE 3110
Low Frequency Characteristics of JFETs JFET IDS – VDS Curves and Pinch off Electronic Devices Laboratory mtinker@utdallas. edu CE/EE 3110
Low Frequency Characteristics of JFETs Plots of gm and rd Versus VGS at VDS = 8. 0 V Electronic Devices Laboratory mtinker@utdallas. edu CE/EE 3110
