Page 1 FET Amplifier Chapter8. FET Amplifier ? FET small-signal model Transconductance g m output impedance r d ? Model applied to some configurations D- & E-MOSFET JFET: Fixed biasing Self biasing V oltage divider Page 2 FET Amplifier Chapter8. FET Amplifier ? FET small-signal model Transconductance g m output impedance r d ? Model applied to some configurations D- & E-MOSFET JFET: Fixed biasing Self biasing V oltage divider FET Amplifier FET Transconductance FET is voltage-controlled device. ?I D =g m ?V GS The V GS controls the I D of an FET. The change in V GS will result a change of the I D in the following manner: where the g m is referred to as transconductance. It is provided as y fs on datasheet. Page 3 FET Amplifier Chapter8. FET Amplifier ? FET small-signal model Transconductance g m output impedance r d ? Model applied to some configurations D- & E-MOSFET JFET: Fixed biasing Self biasing V oltage divider FET Amplifier FET Transconductance FET is voltage-controlled device. ?I D =g m ?V GS The V GS controls the I D of an FET. The change in V GS will result a change of the I D in the following manner: where the g m is referred to as transconductance. It is provided as y fs on datasheet. FET Amplifier FET Input Impedance The input impedance of all commercially available FET is sufficiently large to assume that the terminals approximate an open circuit. Z in = ?? The typical value of Z in is 10 9 ? for JFET and 10 12 ~10 15 ? for MOSFET. Page 4 FET Amplifier Chapter8. FET Amplifier ? FET small-signal model Transconductance g m output impedance r d ? Model applied to some configurations D- & E-MOSFET JFET: Fixed biasing Self biasing V oltage divider FET Amplifier FET Transconductance FET is voltage-controlled device. ?I D =g m ?V GS The V GS controls the I D of an FET. The change in V GS will result a change of the I D in the following manner: where the g m is referred to as transconductance. It is provided as y fs on datasheet. FET Amplifier FET Input Impedance The input impedance of all commercially available FET is sufficiently large to assume that the terminals approximate an open circuit. Z in = ?? The typical value of Z in is 10 9 ? for JFET and 10 12 ~10 15 ? for MOSFET. FET Amplifier FET Output Impedance The output impedance of FET is typically from 20k ? to 100k ?. Z out =r d = 1/y os It is defined by the reciprocal of the slop of the output characteristics, I D ~V DS . On datasheet, output impedance is provided as y os with the units of ?S. Page 5 FET Amplifier Chapter8. FET Amplifier ? FET small-signal model Transconductance g m output impedance r d ? Model applied to some configurations D- & E-MOSFET JFET: Fixed biasing Self biasing V oltage divider FET Amplifier FET Transconductance FET is voltage-controlled device. ?I D =g m ?V GS The V GS controls the I D of an FET. The change in V GS will result a change of the I D in the following manner: where the g m is referred to as transconductance. It is provided as y fs on datasheet. FET Amplifier FET Input Impedance The input impedance of all commercially available FET is sufficiently large to assume that the terminals approximate an open circuit. Z in = ?? The typical value of Z in is 10 9 ? for JFET and 10 12 ~10 15 ? for MOSFET. FET Amplifier FET Output Impedance The output impedance of FET is typically from 20k ? to 100k ?. Z out =r d = 1/y os It is defined by the reciprocal of the slop of the output characteristics, I D ~V DS . On datasheet, output impedance is provided as y os with the units of ?S. FET Amplifier FET AC Equivalent Circuit Shown in the figure is the FET AC equivalent circuit. The control of I d by V gs is included as a controlled current source. The input impedance is represented by the open circuit between G & S. The output impedance is represented by the resistor r d between D & S.Read More

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53 videos|56 docs|97 tests

### Introduction to FET Biasing

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### JFET as Voltage Controlled Resisto

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### Uni-Junction Transistor

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