Easy jFET Curvature Extraction Method … 04/12

This evening I chanced to discover a new (?) method for extracting the jFET modeling parameters: Idss and Vp … this was done with emphasis on low Vp valued devices (2n5484, J201, …) operating in a 9 volt environment …

the method is intuitive as it involves visually estimating when a “proper” transfer profile has been achieved, with values taken directly off the scope // … accuracy in aesthetics !!

the above shows what it’s like to “tune in” the proper amount of back-biasing on the jFET’s Gate in order to get a Parabola-like response on the output current … once the output waveform is set to a near-quadratic profile (ie., no flat part or point at the intersection) the results are read off the scope directly: for this particular 2n5484 device I show Idss = 2.95 mA and Vp = -1.34 volt (@ Vdc = 9vdc) … otoh, Idss measured with a DMM (without correcting for voltage drop in current mirror) gave 2.85 mA …

A very simple method paves the way for reliably extracting jFET device characterization parameters and allows for accurate specification matching, useful in balanced circuits …

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