Fundamental ElectronicsBJT, CMOSReference: Thomas L. Floyd, Electronics Fundamentals: Circuits, Devices, and Applications, Pearson Education Inc

Reference Books

ObjectivesThe History of VLSI

Describe the basic structure and operation of bipolar junction transistors (BJT)

Describe the basic structure and operation of MOSFETs

Describe the basic structure and operation of CMOS

The History of VLSIIC(Integrated Circuits) History Evolutionvacuum tube, single transistor, IC (Integrated Circuits) SSI, MSI, LSI, VLSI, SoC

The History of VLSI1926Lilienfeld proposed FET1947Brattin, Bardin, Schockleyproposed BJT from Bell Lab.1957TI Kilby proposed the first IC1960 Hoerni invent the planar process70sIC composed mainly by pMOS and BJT

The History of VLSI80sIC composed mainly by nMOS and BJT90sIC composed mainly by CMOS and BiCMOS1995NEC, AT&T, Phillips proposed SOC

The evolution of IC technique 19471950196119661971198019851990

TransistorSingle componentSSIMSILSIVLSIULSIGSILogicGate count--------10100~10001000~2000020000~500,000>500,000>10,000,000Produ-ction----8bitROMRAM16/32bitsSOC

Moores Law plotThe transistor count in an IC would double every 18 momths

Main Families in Digital Logic TTL(implemented by BJT)big area, high consumption, high speed MOS small area, low consumption, low speedBiCMOS speed near TTL, area near MOS, hard manufacture

Architecture of BJTsThe bipolar junction transistor (BJT) is constructed with three doped semiconductor regions separated by two pn junctionsRegions are called emitter, base and collector

Architecture of BJTsThere are two types of BJTs, the npn and pnpThe two junctions are termed the base-emitter junction and the base-collector junctionThe term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structureIn order for the transistor to operate properly, the two junctions must have the correct dc bias voltagesthe base-emitter (BE) junction is forward biased(>=0.7V for Si, >=0.3V for Ge)the base-collector (BC) junction is reverse biased

FIGURE Transistor symbols.Thomas L. FloydElectronics Fundamentals, 6eElectric Circuit Fundamentals, 6eCopyright 2004 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458All rights reserved.

Basic circuits of BJT

Operation of BJTsBJT will operates in one of following four regionCutoff region (for digital circuit)Saturation region (for digital circuit)Linear (active) region (to be an amplifier)Breakdown region (always be a disaster)

Operation of BJTs

DC Analysis of BJTsTransistor Currents:IE = IC + IBalpha (DC)IC = DCIEbeta (DC)IC = DCIBDC typically has a value between 20 and 200

DC Analysis of BJTsDC voltages for the biased transistor:Collector voltageVC = VCC - ICRCBase voltageVB = VE + VBE

for silicon transistors, VBE = 0.7 Vfor germanium transistors, VBE = 0.3 V

Q-pointThe base current, IB, is established by the base biasThe point at which the base current curve intersects the dc load line is the quiescent or Q-point for the circuit

Q-point

DC Analysis of BJTsThe voltage divider biasing is widely usedInput resistance is:RIN DCREThe base voltage is approximately:VB VCCR2/(R1+R2)

BJT as an amplifierClass A Amplifiers

Class B Amplifiers

BJT Class A AmplifiersIn a class A amplifier, the transistor conducts for the full cycle of the input signal (360)used in low-power applicationsThe transistor is operated in the active region, between saturation and cutoffsaturation is when both junctions are forward biasedthe transistor is in cutoff when IB = 0The load line is drawn on the collector curves between saturation and cutoff

BJT Class A Amplifiers

BJT Class A AmplifiersThree biasing mode for class A amplifierscommon-emitter (CE) amplifiercommon-collector (CC) amplifiercommon-base (CB) amplifier

BJT Class A AmplifiersA common-emitter (CE) amplifiercapacitors are used for coupling ac without disturbing dc levels

BJT Class A AmplifiersA common-collector (CC) amplifiervoltage gain is approximately 1, but current gain is greater than 1

BJT Class A AmplifiersThe third configuration is the common-base (CB)the base is the grounded (common) terminalthe input signal is applied to the emitteroutput signal is taken off the collectoroutput is in-phase with the inputvoltage gain is greater than 1current gain is always less than 1

BJT Class B AmplifiersWhen an amplifier is biased such that it operates in the linear region for 180 of the input cycle and is in cutoff for 180, it is a class B amplifierA class B amplifier is more efficient than a class AIn order to get a linear reproduction of the input waveform, the class B amplifier is configured in a push-pull arrangementThe transistors in a class B amplifier must be biased above cutoff to eliminate crossover distortion

BJT Class B Amplifiers

The BJT as a SwitchWhen used as an electronic switch, a transistor normally is operated alternately in cutoff and saturationA transistor is in cutoff when the base-emitter junction is not forward-biased. VCE is approximately equal to VCCWhen the base-emitter junction is forward-biased and there is enough base current to produce a maximum collector current, the transistor is saturated

The BJT as a Switch

An example -- NOR

Architecture of MOS Field-Effect Transistors (FETs)The metal-oxide semiconductor field-effect transistor (MOSFET) : the gate is insulated from the channel by a silicon dioxide (SiO2) layer

Architecture of MOS Field-Effect Transistors (FETs)Two types of MOSFETs depletion type (D-MOSFETs) have a physical channel between Drain and Source, with no voltage applied to the Gateenhancement type (E-MOSFETs) have no physical Drain-Source channel

Architecture of MOS Field-Effect Transistors (FETs)D-MOSFET Channel may be enhanced or restricted by gate voltage

E-MOSFETChannel is created by gate voltage

Simplified symbol

Biasing Circuits

FET AmplifiersVoltage gain of a FET is determined by the transconductance (gm) with units of Siemens (S)gm = Id / VgThe D-MOSFET may also be zero-biasedThe E-MOSFET requires a voltage-divider-biasAll FETs provide extremely high input resistance

Principle of MOSFETfor E-MOS (n-channel)(+)

Principle of MOSFET for E-MOS (n-channel)The threshold voltage

Principle of MOSFET for E-MOS (n-channel)

Principle of MOSFET for D-MOS (n-channel)

Principle of MOSFET for D-MOS (n-channel)

Voltage-current relations

p-cnannel MOS(pMOS) bodyAll the characteristics are similar to NMOS.+--+++++++

An inverter

Voltage transfer-- see the time delay

Complementary MOS(CMOS) VssinputoutputVdd