Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download OtherTransistorTopologies30MarchAnd1April
Document related concepts
no text concepts found
Transcript
Other Transistor Topologies 30 March and 1 April 2015 JFET Junction Field Effect Transistor • The two gate terminals are tied together to form single gate connection; the source terminal is grounded • The flow of electric charge through a PN JFET is controlled by constricting the current-carrying channel; the width of the channel is controlled by the gate voltage through varying the depletion region at the PN junction at the interface between the gate and the channel • The current also depends on the electric field between source and drain 1 Structure of JFET N-channel JFET • a long channel of n-type (N-channel) or p-type (p-channel) semiconductor. Two ohmic contacts with each at one end of the channel: the source and the drain • The gate (control) terminal has doping opposite to that of the channel, so there is a PN junction at the interface between the junction and the channel. The contact from gate to outside is also ohmic. 2 3 4 I-V relationship of PN JFET Nonsaturation region (linear region) Saturation region 5 Other Features of PN JFET • JFET is unipolar device since only majority carriers transport in the channel • The source and drain region are interchangeable • N-channel devices have greater conductivity than p-channel types, since electrons have higher mobility than holes • The gate current is approximately zero since the PN junction is reverse biased Symbols of JFET (arrow represents the polarity of the PN junction) 6 Comparisons of Transistors BJT Structure NPN: n++p+n PNP: p++n+p Current transport Diffusion Carriers involved in current transport Bipolar: electrons and holes Current at terminals IC=βIB= (1/α) IE (Forward active mode) IC=f(VBE, VBC) MOSFET n(p)-type inversion layer structure as channel from S to D Drift Unipolar NMOS: electrons PMOS: holes IG=0 ID=f(VGS, VDS) JFET Inversed biased PN junction between the gate and channel from S to D Drift Unipolar: N-channel: electrons P-channel: holes IG≈0 ID=f(VGS, VDS) 7 Comparisons of Transistors (Cont’d) BJT MOSFET JFET Symbols NPN Applications PNP • Current-controlled current amplifier • Switch for digital signal • Discrete circuits NMOS PMOS • Voltage-controlled current amplifier • Switch for digital signal • IC circuits N-channel P-channel • Voltage-controlled current amplifier • Switch for digital signal • IC circuits • MESFET can be used in higherfrequency than PN-JFET due to higher electron mobility in GaAs 8 9 10 11 12
