Question

Interpretation: 1. Which region is the JFET operating in the voltage controlled resistor? 2. How is this different than using the JFET as an amplifier? If you encountered a JFET in a circuit, what would you measure to determine if the device is operating in the Ohmic or Active Region? Why are scopes used so often for AC measurements rather than the DMM? (Examine the Frequency Column in the first table in the Appendix and followed by the another make and model, notice its frequency range.) Would either DMM be of any use at 100 kHz? 3. EE-223_Lab02_Fall_2017.docx Page 5 of6

Answer 1

JFET in Ohmic-Region act as a voltage-controlled resistor. Vgs ( Gate to Source ) voltage is used to control the slope of JFET I-V curve which is resistance ( slope ).

JFET active region is different from JFET ohmic region in the sense that in active region drain current shoots up drastically and JFET responds amplification effect. If we encounter a JFET circuit then, we should measure drain current and note successive changes for the corresponding change in Vds (drain to source voltage). If there is no significant change then active region and if a linear change observed then ohmic region.

Although DMMs reveal precise amplitude and frequencies values of AC signals. Scopes not only show readings they are used to visualize the shape and form as well which DMMs can not. DMM circuits are not suitable for high-frequency signals ( like 100 KHz) and will give errors. So it is best practice and routine to use scopes for AC signal analysis.