PERTEMUAN XV PENGERTIAN DAN PRINSIP KERJA JFET LANJUTAN MUTIARA WIDASARI SITOPU, S.T., M.T. DASAR ELEKTRONIKA SOLID STATE N-CHANNEL JFET N channel JFET: Major structure is n-type material (channel) between embedded p-type material to form 2 pn junction. In the normal operation of an n-channel device, the Drain (D) is positive with respect to the Source (S). Current flows into the Drain (D), through the channel, and out of the Source (S) Because the resistance of the channel depends on the gate-to-source voltage (VGS), the drain current (ID) is controlled by that voltage INTRODUCTION (FET) Field-effect transistor (FET) are important devices such as BJTs Also used as amplifier and logic switches What is the difference between JFET and BJT? BJT IS CURRENT-CONTROLLED FET IS VOLTAGE-CONTROLLED TYPES OF FIELD EFFECT TRANSISTORS (THE CLASSIFICATION) n-Channel JFET FET JFET p-Channel JFET MOSFET (IGFET) Enhancement MOSFET n-Channel EMOSFET p-Channel EMOSFET Depletion MOSFET n-Channel DMOSFET p-Channel DMOSFET N-CHANNEL JFET.. INTRODUCTION.. (ADVANTAGES OF FET OVER BJT) High input impedance (M) (Linear AC amplifier system) Temperature stable than BJT Smaller than BJT Can be fabricated with fewer processing BJT is bipolar – conduction both hole and electron FET is unipolar – uses only one type of current carrier Less noise compare to BJT Usually use as an Amplifier and logic switch JUNCTION FIELD-EFFECT TRANSISTOR.. There are 2 types of JFET n-channel JFET p-channel JFET Three Terminal Drain – D Gate -G Source – S SYMBOLS Drain Drain Gate Gate Source n-channel JFET Source p-channel JFET JFET CHARACTERISTIC FOR VGS = 0 V AND 0<VDS<|VP| To start, suppose VGS=0 Then, when VDSis increased, ID increases. Therefore, IDis proportional to VDSfor small values of VDS For larger value of VDS, as VDSincreases, the depletion layer become wider, causing the resistance of channel increases. After the pinch-off voltage (Vp) is reached, the ID becomes nearly constant (called as ID maximum, IDSS-Drain to Source current with Gate Shorted) JFET FOR VGS = 0 V AND 0<VDS<|VP| Channel becomes narrower as VDS is increased PINCH-OFF (VGS = 0 V, VDS = VP). ID versus VDS for VGS = 0 V and 0<VDS<|Vp| JFET Characteristic Curve JFET FOR (APPLICATION OF A NEGATIVE VOLTAGE TO THE GATE OF A JFET ) JFET CHARACTERISTIC CURVE.. For negative values of VGS, the gate-to-channel junction is reverse biased even with VDS=0 Thus, the initial channel resistance of channel is higher. The resistance value is under the control of VGS If VGS = pinch-off voltage(VP) The device is in cutoff (VGS=VGS(off) = VP) The region where ID constant – The saturation/pinchoff region The region where ID depends on VDS is called the linear/ohmic region CHARACTERISTICS FOR N-CHANNEL JFET TRANSFER CHARACTERISTICS The input-output transfer characteristic of the JFET is not as straight forward as it is for the BJT. In BJT: IC= IB which is defined as the relationship between IB (input current) and IC (output current). TRANSFER CHARACTERISTICS.. • IN JFET, THE RELATIONSHIP BETWEEN VGS (INPUT VOLTAGE) AND ID (OUTPUT CURRENT) IS USED TO DEFINE THE TRANSFER CHARACTERISTICS. IT IS CALLED AS SHOCKLEY’S EQUATION: V GS 1 VP 2 ID = IDSS VP=VGS (OFF) The relationship is more complicated (and not linear) As a result, FET’s are often referred to a square law devices TRANSFER CHARACTERISTICS… Defined by Shockley’s equation: V I D IDSS 1 GS VGS (off ) 2 VP VGS (off ) Relationship between IDand VGS. Obtaining transfer characteristic curve axis point from Shockley: When VGS= 0 V, ID= IDSS When VGS= VGS(off)or Vp, ID= 0 mA Transfer Characteristics JFET Transfer Characteristic Curve JFET Characteristic Curve EXERCISE 1 Sketch the transfer defined by IDSS= 12 mA dan VGS(off) = - 6 VGS ID 0 IDSS 0.3Vp IDSS/2 0.5Vp IDSS/4 Vp 0 mA ID VGS = VP1 I DSS 2 VGS ID = IDSS 1 VP EXERCISE 1 Sketch the transfer defined by IDSS= 12 mA dan VGS(off) = Vp=- 6 IDSS VGS ID = IDSS 1 VP 2 VGS =0.3VP VGS =0.5VP IDSS/2 IDSS/4 ID VGS = VP1 I DSS ANSWER 1 EXERCISE 2 Sketch the transfer defined by IDSS= 4 mA dan VGS(off) = 3 V VGS ID 0 IDSS 0.3Vp IDSS/2 0.5Vp IDSS/4 Vp 0 mA ID VGS = VP1 I DSS 2 VGS ID = IDSS 1 VP EXERCISE 2 Sketch the transfer defined by IDSS= 4 mA dan VGS(off)= 3V IDSS VGS ID = IDSS 1 VP 2 IDSS/2 IDSS/4 VGS =0.3VP VP VGS =0.5VP ID VGS = VP1 I DSS Answer 2 ANSWER 2 SEKIAN DAN TERIMA KASIH