Subject Name: Electronic Circuits Subject Code:10cs32 Prepared By: Supriya.V.Sullad Department: CSE Date:26-8-2014 4/10/2019

Overview Bipolar Junction Transistor V/S Field Effect Transistor Junction Field Effect Transistor Metal Oxide Field Effect Transistor JFETs V/S MOSFETs Handling MOSFETs Biasing MOSFETs FET Applications VMOS Devices CMOS Devices IGBTs 4/10/2019

BJT V/S FET BJTs are Current Controlled Devices,FETs are Voltage Controlled Devices. BJTs are Bi-Polar Devices, FETs are Unipolar Devices. Input Impedance of FET is very High (100MΩ),while BJT has less than 1MΩ. Gain of FET is smaller compared to BJT FETs have poor sensitivity to the changes in the input Fets are more sensitive to handle than BJT’s 4/10/2019

Junction Field Effect Transistor There are Two PN Junctions formed between the semiconductor channel and the semiconductor layers. The three terminals are Source,Gate and Drain. 4/10/2019

When Vgs =0 ,Id increases linearly with increase in Vds untill Vds reaches Saturation effect referred as Pinch-Off voltage (Vp). For N-Channel FET,Voltage Vgs is negative,while gate terminal is made more negative than the source. Voltage Vgs is positive for P-channel FET. 4/10/2019

The drain resistance rd in the saturation region is given by: Rd=r0/(1-Vgs/Vp)2 The relation between output current Id and Vgs is gven by Id=Idss(1-Vgs/Vp)2 As in the equation,there is square law relation between Id and Vgs. Since JFETs are usefull in Radio and TV recievers. 4/10/2019

Metal oxide semiconductor Field Effect Transistor There are two types of mosfets based on their Construction and mode of Operation: Depletion Mosfet and Enhancement Mosfet. In Depletion Mode for a N-Channel device, there is a channel that exists between Two N+ layers . 4/10/2019

In Depletion Region,to drive the Current to the Drain,If gate is 0/-ve and Vds is +ve ,Holes of P-subsrate arrracts to to–wards the Junction and Current flows due to recombination of both holes and electrons.This reduces the no. of electron current flow to the Drain. 4/10/2019

Enhancement Mosfet 4/10/2019

In Enhancement Region,there is no Physical Channel that exixts between the two N+ regions for N type Mosfet. Vgs and Vds both are given +ve potential such that,electrons from N+ region are attraced towards the gate and the drain Current Flows.While holes of P-Substrate move away from Sio2 layer.As Vgs is increased there is enhanced flow of electron current through the Drain Treminals. Vds(sat)=Vgs-Vt 4/10/2019

Differences between JFET’s and MOSFET. Id=K(Vgs-Vt)2 Differences between JFET’s and MOSFET. The input resistance offerred by Mosfet is more. Jfets have higher Drain Resistance than Mosfet The Lekage current of Mosfet is smaller than Fet. Mosfet’s are easier to construct and are more widely used than JFETs. 4/10/2019

Handling MOSFETs The person handling Mosfet should always touch ground before handling the device This allows discharge of the charge before handling the device. By Connecting Zener diodes back-to-Back,between the gate and source ,it ensures that Vgs never exceeds the specified maximum rating of the device. 4/10/2019

Depletion and Enhancement Mosfet’s 4/10/2019

In Depletion mode,Vgs is given +ve voltage. Biasing Mosfet In Depletion mode,Vgs is given +ve voltage. In Enhancement method there exists a Feedback between Drain and the gate terminal, via the resistor Rg. In this case, Vdd-IdRd-Vgs=0 Vgs=Vdd-IdRd Vds=Vdd-IdRd Hence Vds=Vgs 4/10/2019

Voltage Variable Resistors(VVR) Oscillators FET APPLICATIONS Fet is used as an Amplifier Analog Switch Multiplexers Current Limiters Voltage Variable Resistors(VVR) Oscillators 4/10/2019

VMOSFET DEVICE 4/10/2019

VMOS Devices VMOS is a Vertical Structure Mosfet. The operation of VMOSFET is similar to E-MOSFET i.e no channel exists between the two N+ layers. For +ve Vgs ,a N-Channel is formed closed to the gate in the vertical direction. VMOS devices have smaller channel lengths and larger contact area between Channel and N+ doped layers. 4/10/2019

CMOS INVERTER 4/10/2019

VMosfets have reduced resistance region,power dissipation VMOS devices have Faster Switching times CMOS DEVICES: (Complementary Metal Oxide Semiconductor field effect Transistor) It has both P-type and N-type E-Mosfet’s diffused on the same chip. Have higher input impedance and lower Power Consumption and slower switching speed compared to BJT’s. 4/10/2019

Cmos device works as an inverter When the input voltage is at Low level,the Vg2 S2 of the P-Channel E-Mosfet is equal to –Vss.And the Mosfet is in the ON State. When the input is at High logic equal to Vss,the VgsS2 of P-Channel E-Mosfet is at 0V and Mosfet is OFF State. 4/10/2019

IGBT Construction 4/10/2019

Insulated Gate Bipolar Transistor(IGBT) IGBTs have Fast Switching times as MOSFET’s and Lower turn on voltages and larger blocking voltages as BJTs The Construction of IGBT is similar to VMOSFET except that N+ drain is replaced by P+collector layer forming a vertical PNP Transistor. The initial offset in the characteristics is around 0.7V because of the ON –State voltage While the Steep is due to current flow which is due to both electrons and holes. 4/10/2019

IGBTs offers slow Switching speeds especially during Turn-Off. While IGBT’s are susceptable to a gate insulation damage by electro static discharge. 4/10/2019

Thank you 4/10/2019