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Low Frequency Characteristics of JFETs

Low Frequency Characteristics of JFETs. Low Frequency Characteristics of Junction Field Effect Transistors. Low Frequency Characteristics of JFETs. Junction FET (JFET) one form of an FET transistor Voltage-variable depletion width used to control transistor operation

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Low Frequency Characteristics of JFETs

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  1. Low Frequency Characteristics of JFETs Low Frequency Characteristics of Junction Field Effect Transistors

  2. Low Frequency Characteristics of JFETs • Junction FET (JFET) one form of an FET transistor • 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

  3. Low Frequency Characteristics of JFETs Variation of depletion width across JFET channel (a) and current-voltage characteristics versus gate voltage (b).

  4. Low Frequency Characteristics of JFETs 2N5485 n-channel JFET IDS-VDS characteristics (upper left), input-output characteristic (iD(sat.) vs vGS) of a JFET (upper right), and small signal model of a JFET in pinched off mode of operation (bottom).

  5. Low Frequency Characteristics of JFETs • Measurements: • ID(Sat.) = IDSS(1+VGS/VP)2 • VP = -VGS + VDS(Sat.) • gm = ΔiD/ΔνGS (νDS = const.) • rd = ΔνDS/ΔiD (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

  6. Low Frequency Characteristics of JFETs JFET IDS – VDS Curves

  7. Low Frequency Characteristics of JFETs JFET IDS – VDS Curves and Pinch off

  8. Low Frequency Characteristics of JFETs Plots of gm and rd Versus VGS at VDS = 8.0 V

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