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MPF102 Jfet Chopper Circuit

2017-08-15 19:00  
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JFET can incor­porate the amplifying action as well as feedbackaction. It, therefore, acts well as a phase shift oscillator.The high input impedance of FET is especially very valuable in phase-shift oscillators in order to minimize the loading effect. A typical phase shift oscillator employing N-channel JFET is shown in figure.A JFET (MPF102 ) is used to chop a dc signal for amplification in an ac coupled amplifier. Q3 is the chopper element and Q1-Q2 forms the multivibrator to derive a chopping signal.Rr sets the bias on the  FET  to keep the drive to MPF102 as low as possible.FETs are widely used as input amplifiers in oscilloscopes, electronic voltmeters and other measuring and testing equipment because of their high input impedance.FET chopper like a transistor chopper suffers from the leakage current which flows when the device is OFF. A method for compensating for the leakage current of FET is shown by the dashed portion.

Jfet Chopper Circuit Circuit