1. Electronic Devices Laboratory mtinker@utdallas.edu CE/EE 3110 Low Frequency Characteristics of Junction Field Effect Transistors Low Frequency Characteristics of JFETs

2. Electronic Devices Laboratory mtinker@utdallas.edu CE/EE 3110 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 Low Frequency Characteristics of JFETs

3. Electronic Devices Laboratory mtinker@utdallas.edu CE/EE 3110 Variation of depletion width across JFET channel (a) and current-voltage characteristics versus gate voltage (b). Low Frequency Characteristics of JFETs

4. Electronic Devices Laboratory mtinker@utdallas.edu CE/EE 3110 2N5485 n-channel JFET I DS -V DS characteristics (upper left), input- output 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). Low Frequency Characteristics of JFETs

5. Electronic Devices Laboratory mtinker@utdallas.edu CE/EE 3110 Measurements: 1)I D(Sat.) = I DSS (1+V GS /V P ) 2 2)V P = -V GS + V DS(Sat.) 3)g m = Δi D /Δν GS (ν DS = const.) 4)r d = Δν DS /Δi D (ν GS = const.) Experimental values for V p, I D(Sat.), g m, and r d and theoretical values for I D(Sat.). Plot the I DS versus V DS characteristic and show pinch-off locus in the plot Plot both the experimental and theoretical curves for I D(Sat.) versus ν GS Determine g m and r d at ν DS = 8 V Low Frequency Characteristics of JFETs

6. Electronic Devices Laboratory mtinker@utdallas.edu CE/EE 3110 Low Frequency Characteristics of JFETs JFET I DS – V DS Curves

7. Electronic Devices Laboratory mtinker@utdallas.edu CE/EE 3110 Low Frequency Characteristics of JFETs JFET I DS – V DS Curves and Pinch off

8. Electronic Devices Laboratory mtinker@utdallas.edu CE/EE 3110 Low Frequency Characteristics of JFETs Plots of g m and r d Versus V GS at V DS = 8.0 V