DOCSLIB.ORG

5.10 Equivalent Circuit of a Bipolar Junction Transistor

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
5.10 Equivalent Circuit of a Bipolar Junction Transistor Introduction to Electronic Devices, Fall 2006, Dr. D. Knipp Introduction to Electronic Devices (Course Number 300331) Fall 2006 Bipolar Transistors Information: http://www.faculty.iu- Dr. Dietmar Knipp bremen.de/dknipp/ Assistant Professor of Electrical Engineering Source: Apple Ref.: Apple Ref.: IBM Critical 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 101 dimension (m) Ref.: Palo Alto Research Center Bipolar Transistor 1 Introduction to Electronic Devices, Fall 2006, Dr. D. Knipp Introduction to Electronic Devices 5 Bipolar Transistors 5.1 Introduction 5.2 Basic transistor operation 5.3 Transistor under zero bias 5.4 Transistor under bias conditions 5.4.1 Shockley Assumptions 5.4.2 The ideal transistor equation 5.4.3 The transistor equation in its general form 5.4.4 Modes of Operation 5.8.1 The active mode 5.8.2 The Saturation mode 5.8.3 The cutoff mode 5.8.4 The inversion mode 5.5 Transport and gain factors 5.5.1 The Emitter efficiency 5.5.2 The Transport factor 5.5.3 The Common-base current gain 5.5.5 The summary of the transport and gain factors Bipolar Transistor 2 Introduction to Electronic Devices, Fall 2006, Dr. D. Knipp 5.6 Transistor Design 5.6.1 The transport factor 5.6.2 The Emitter Efficiency 5.7 Bipolar Transistors as Amplifiers 5.7.1 Common base circuit 5.7.2 Common emitter circuit 5.7.3 The Early Effect 5.8 Transfer characteristic and gain 5.9 Device parameters 5.10 Equivalent circuit of a bipolar junction transistor References Bipolar Transistor 3 Introduction to Electronic Devices, Fall 2006, Dr. D. Knipp 5.1 Introduction The transistor (Germanium point contact transistor) was invited by Barttain, Bardeen and Shockley in 1947. As the name already implies it is a bipolar device (like a diode), which means that both electrons and holes (minority and majority carriers) contribute to the overall current flow. The bipolar junction transistor (BJT) is one of the most important semiconductor devices. The transistor is used for high speed circuits, analog circuits and power applications. The underlying electronic transport mechanisms of bipolar junction transistors (BJT) and diodes are similar. Both devices are diffusion controlled devices. Therefore, the influence of the drift current on the total current is negligible. The operating principle of bipolar devices is different from the behavior of unipolar device like a Field Effect Transistors (FETs), where the current is either controlled by electrons or holes. Furthermore, a field effect transistor is a drift controlled electronic device. Bipolar Transistor 4 Introduction to Electronic Devices, Fall 2006, Dr. D. Knipp 5.1 Introduction A bipolar transistor (like all other transistors) is a three (four) terminal device. The device consists of an input and an output loop. The device is designed in such a ways that small input changes of a current or/and a voltage result in large changes of the output current or/and voltage. Schematic cross section of a pnp The BJT device structure consists of two transistor. The transistor is pn junctions. The device can be implemented in a p-type implemented as an pnp or a npn substrate. The n-type and the p+- structure. Each of the doped regions is type regions are formed by connected with one of the terminals: diffusion of dopants in the p-type Base, Emitter or Collector. The three substrate. The electrodes are regions of a BJT are formed by the formed by metal contacts. diffusion of a doping profiles in a substrate. Ref.: M.S. Sze, Semiconductor Devices Bipolar Transistor 5 Introduction to Electronic Devices, Fall 2006, Dr. D. Knipp 5.1 Introduction The operation principle of a bipolar transistor relies on the fact that the base region of the transistor is a very thin region, so that the two diodes affect each other. The thickness of the base in controlled by the manufacturing (diffusion) process. In terms of applications pure analog integrated circuits are getting less important. Nowadays the technology shifts towards BiCMOS technology. BiCMOS is a combination of bipolar technology and metal oxide semiconductor technology (technology required to manufacture field effect transistors). It allows the realization of analog and digital circuits on a single chip. 5.2 Basic transistor operation The two possible device structures of a bipolar transistor or Pnp- and a npn- structures. Bipolar transistors can operate in four modes of operation, depending on the voltage applied to the base-emitter and the base-collector junction. The four modes of operation are: Active mode, inversion mode, cutoff mode, Saturation mode. Bipolar Transistor 6 Introduction to Electronic Devices, Fall 2006, Dr. D. Knipp 5.2 Basic transistor operation In order to realize an amplifier the BJT will be operated in the active mode. In the following the basic operating principle of a bipolar transistor in the active mode will be presented. The + and – signs indicate the polarities pnp-transistor of the voltages applied to the terminals under normal operating conditions (active mode). In the active mode the emitter base diode is forward biased (VEB>0) and the base collector diode is reverse biased (VCB<0). npn-transistor Ref.: M.S. Sze, Semiconductor Devices Bipolar Transistor 7 Introduction to Electronic Devices, Fall 2006, Dr. D. Knipp 5.2 Basic transistor operation On this slide the + and – signs indicate the direction of the current flow. IB = IE − IC The npn-structure is complementary pnp-transistor to the pnp structure. As a consequence the current flow and the voltage polarities are reversed. In the following we will discuss the electronic transport of a pnp transistor. npn-transistor Ref.: M.S. Sze, Semiconductor Devices Bipolar Transistor 8 Introduction to Electronic Devices, Fall 2006, Dr. D. Knipp 5.3 Bipolar Junction Transistors under zero bais At first the BJT will be studied in thermal equilibrium. All three terminals of the device are grounded. Under thermal equilibrium the Fermi level is constant throughout the entire device structure. As a consequence the derivative of the Fermi level is zero, so that the overall current flowing through the device is zero. The following device structure is used for the discussion: The emitter is (much) heavier doped than the base and the base is again heavier doped than the collector. The base region is much shorter than the emitter and the collector region. The base width of the base region is much shorter than the diffusion length of the minority carriers. Therefore, the two pn-junctions affect each other. If the base-region would be much longer than the diffusion length of the minority carriers in the base region of the two pn-junctions would behave like two separate diodes. The operation of the diodes would be independent of each other. The electric field distribution in the BJT can be calculated by solving the Poisson equation. As a consequence of the doping profile in the individual regions of the device the maximum electric field and the built-in voltage for the base/emitter junctions is higher than the maximum electric field and the built-in voltage for the base/collector junction (under thermal equilibrium). Bipolar Transistor 9 Introduction to Electronic Devices, Fall 2006, Dr. D. Knipp 5.3 Bipolar Junction Transistor under zero bias Throughout the following discussion it is assumed that two abrupt junctions are formed. As a consequence the electric field distribution outside of the depletion regions is zero. The formation of the space charge region for a BJT is comparable with the formation of the space charge region of a diode. pnp-transistor (a) pnp-transistor under thermal equilibrium (all terminals grounded). (b) Doping profile of an abrupt pnp structure, (c) Electric field profile, (d) Energy band diagram Ref.: M.S. Sze, Semiconductor Devices Bipolar Transistor 10 Introduction to Electronic Devices, Fall 2006, Dr. D. Knipp 5.3 Bipolar Junction Transistor under zero bias There are technological and a physical reasons for the different doping profiles in the individual regions of the device: Technological: The fabrication of a BJT requires two diffusion steps to form three regions with different doping concentrations. In the first diffusion step the base has to be formed and the already existing dopants in the material (in the substrate) have to be compensated or over compensated. In the second diffusion step the doping concentration has to be increased again to compensate the incorporated dopants of the first diffusion step. Physical: The goal of the transistor design is the realization of transistors with high current and/or voltage gain. High current and voltages gains can be achieved if the doping concentration in the base is lower than the doping concentration in the emitter. The underlying physical reasons for this particular behavior will be discussed in the chapter on transport and gain factors. Bipolar Transistor 11 Introduction to Electronic Devices, Fall 2006, Dr. D. Knipp 5.4 Transistor under bias conditions Before deriving the ideal bipolar junction transistor equations the basic operating principle of BJT under biasing conditions will be described. Here we will concentrate on a common base bipolar transistor in active mode as this is the most important mode of operation. In this case the base/emitter junction is in forward bias and the base/collector junction operates under reverse bias conditions. The input and the output loop share the base terminal. Therefore, the circuit is called a common base circuit. As a consequence of the applied bias voltages the width of the depletion regions is changed. Since the base emitter junctions is under forward bias holes are injected via the emitter and electrons are injected via the base.
Load more

Recommended publications
  • Chapter 7: AC Transistor Amplifiers
    Chapter 7: Transistors, part 2 Chapter 7: AC Transistor Amplifiers The transistor amplifiers that we studied in the last chapter have some serious problems for use in AC signals. Their most serious shortcoming is that there is a “dead region” where small signals do not turn on the transistor. So, if your signal is smaller than 0.6 V, or if it is negative, the transistor does not conduct and the amplifier does not work. Design goals for an AC amplifier Before moving on to making a better AC amplifier, let’s define some useful terms. We define the output range to be the range of possible output voltages. We refer to the maximum and minimum output voltages as the rail voltages and the output swing is the difference between the rail voltages. The input range is the range of input voltages that produce outputs which are not at either rail voltage. Our goal in designing an AC amplifier is to get an input range and output range which is symmetric around zero and ensure that there is not a dead region. To do this we need make sure that the transistor is in conduction for all of our input range. How does this work? We do it by adding an offset voltage to the input to make sure the voltage presented to the transistor’s base with no input signal, the resting or quiescent voltage , is well above ground. In lab 6, the function generator provided the offset, in this chapter we will show how to design an amplifier which provides its own offset.
    [Show full text]
  • PH-218 Lec-12: Frequency Response of BJT Amplifiers
    Analog & Digital Electronics Course No: PH-218 Lec-12: Frequency Response of BJT Amplifiers Course Instructors: Dr. A. P. VAJPEYI Department of Physics, Indian Institute of Technology Guwahati, India 1 High frequency Response of CE Amplifier At high frequencies, internal transistor junction capacitances do come into play, reducing an amplifier's gain and introducing phase shift as the signal frequency increases. In BJT, C be is the B-E junction capacitance, and C bc is the B-C junction capacitance. (output to input capacitance) At lower frequencies, the internal capacitances have a very high reactance because of their low capacitance value (usually only a few pf) and the low frequency value. Therefore, they look like opens and have no effect on the transistor's performance. As the frequency goes up, the internal capacitive reactance's go down, and at some point they begin to have a significant effect on the transistor's gain. High frequency Response of CE Amplifier When the reactance of C be becomes small enough, a significant amount of the signal voltage is lost due to a voltage-divider effect of the source resistance and the reactance of C be . When the reactance of Cbc becomes small enough, a significant amount of output signal voltage is fed back out of phase with the input (negative feedback), thus effectively reducing the voltage gain. 3 Millers Theorem The Miller effect occurs only in inverting amplifiers –it is the inverting gain that magnifies the feedback capacitance. vin − (−Av in ) iin = = vin 1( + A)× 2π × f ×CF X C Here C F represents C bc vin 1 1 Zin = = = iin 1( + A)× 2π × f ×CF 2π × f ×Cin 1( ) Cin = + A ×CF 4 High frequency Response of CE Amp.: Millers Theorem Miller's theorem is used to simplify the analysis of inverting amplifiers at high-frequencies where the internal transistor capacitances are important.
    [Show full text]
  • Cascode Amplifiers by Dennis L. Feucht Two-Transistor Combinations
    Cascode Amplifiers by Dennis L. Feucht Two-transistor combinations, such as the Darlington configuration, provide advantages over single-transistor amplifier stages. Another two-transistor combination in the analog designer's circuit library combines a common-emitter (CE) input configuration with a common-base (CB) output. This article presents the design equations for the basic cascode amplifier and then offers other useful variations. (FETs instead of BJTs can also be used to form cascode amplifiers.) Together, the two transistors overcome some of the performance limitations of either the CE or CB configurations. Basic Cascode Stage The basic cascode amplifier consists of an input common-emitter (CE) configuration driving an output common-base (CB), as shown above. The voltage gain is, by the transresistance method, the ratio of the resistance across which the output voltage is developed by the common input-output loop current over the resistance across which the input voltage generates that current, modified by the α current losses in the transistors: v R A = out = −α ⋅α ⋅ L v 1 2 β + + + vin RB /( 1 1) re1 RE where re1 is Q1 dynamic emitter resistance. This gain is identical for a CE amplifier except for the additional α2 loss of Q2. The advantage of the cascode is that when the output resistance, ro, of Q2 is included, the CB incremental output resistance is higher than for the CE. For a bipolar junction transistor (BJT), this may be insignificant at low frequencies. The CB isolates the collector-base capacitance, Cbc (or Cµ of the hybrid-π BJT model), from the input by returning it to a dynamic ground at VB.
    [Show full text]
  • I. Common Base / Common Gate Amplifiers
    I. Common Base / Common Gate Amplifiers - Current Buffer A. Introduction • A current buffer takes the input current which may have a relatively small Norton resistance and replicates it at the output port, which has a high output resistance • Input signal is applied to the emitter, output is taken from the collector • Current gain is about unity • Input resistance is low • Output resistance is high. V+ V+ i SUP ISUP iOUT IOUT RL R is S IBIAS IBIAS V− V− (a) (b) B. Biasing = /α ≈ • IBIAS ISUP ISUP EECS 6.012 Spring 1998 Lecture 19 II. Small Signal Two Port Parameters A. Common Base Current Gain Ai • Small-signal circuit; apply test current and measure the short circuit output current ib iout + = β v r gmv oib r − o ve roc it • Analysis -- see Chapter 8, pp. 507-509. • Result: –β ---------------o ≅ Ai = β – 1 1 + o • Intuition: iout = ic = (- ie- ib ) = -it - ib and ib is small EECS 6.012 Spring 1998 Lecture 19 B. Common Base Input Resistance Ri • Apply test current, with load resistor RL present at the output + v r gmv r − o roc RL + vt i − t • See pages 509-510 and note that the transconductance generator dominates which yields 1 Ri = ------ gm µ • A typical transconductance is around 4 mS, with IC = 100 A • Typical input resistance is 250 Ω -- very small, as desired for a current amplifier • Ri can be designed arbitrarily small, at the price of current (power dissipation) EECS 6.012 Spring 1998 Lecture 19 C. Common-Base Output Resistance Ro • Apply test current with source resistance of input current source in place • Note roc as is in parallel with rest of circuit g v m ro + vt it r − oc − v r RS + • Analysis is on pp.
    [Show full text]
  • ECE 255, MOSFET Basic Configurations
    ECE 255, MOSFET Basic Configurations 8 March 2018 In this lecture, we will go back to Section 7.3, and the basic configurations of MOSFET amplifiers will be studied similar to that of BJT. Previously, it has been shown that with the transistor DC biased at the appropriate point (Q point or operating point), linear relations can be derived between the small voltage signal and current signal. We will continue this analysis with MOSFETs, starting with the common-source amplifier. 1 Common-Source (CS) Amplifier The common-source (CS) amplifier for MOSFET is the analogue of the common- emitter amplifier for BJT. Its popularity arises from its high gain, and that by cascading a number of them, larger amplification of the signal can be achieved. 1.1 Chararacteristic Parameters of the CS Amplifier Figure 1(a) shows the small-signal model for the common-source amplifier. Here, RD is considered part of the amplifier and is the resistance that one measures between the drain and the ground. The small-signal model can be replaced by its hybrid-π model as shown in Figure 1(b). Then the current induced in the output port is i = −gmvgs as indicated by the current source. Thus vo = −gmvgsRD (1.1) By inspection, one sees that Rin = 1; vi = vsig; vgs = vi (1.2) Thus the open-circuit voltage gain is vo Avo = = −gmRD (1.3) vi Printed on March 14, 2018 at 10 : 48: W.C. Chew and S.K. Gupta. 1 One can replace a linear circuit driven by a source by its Th´evenin equivalence.
    [Show full text]
  • Dynamic Microphone Amplifier
    Dynamic Microphone Preamp Description: A low noise pre-amplifier suitable for amplifying dynamic microphones with 200 to 600 ohm output impedance. Notes: This is a 3 stage discrete amplifier with gain control. Alternative transistors such as BC109C, BC548, BC549, BC549C may be used with little change in performance. The first stage built around Q1 operates in common base configuration. This is unusuable in audio stages, but in this case, it allows Q1 to operate at low noise levels and improves overall signal to noise ratio. Q2 and Q3 form a direct coupled amplifier, similar to my earlier mic preamp . Input and Output Impedance: As the signal from a dynamic microphone is low typically much less than 10mV, then there is little to be gained by setting the collector voltage voltage of Q1 to half the supply voltage. In power amplifiers, biasing to half the supply voltage allows for maximum voltage swing, and highest overload margin, but where input levels are low, any value in the linear part of the operating characteristics will suffice. Here Q1 operates with a collector voltage of 2.4V and a low collector current of around 200uA. This low collector current ensures low noise performance and also raises the input impedance of the stage to around 400 ohms. This is a good match for any dynamic microphone having an impedances between 200 and 600 ohms. The output impedance at Q3 is low, the graph of input and output impedance versus frequency is shown below: Gain and Frequency Response: The overall gain of this pre-amplifier is around +39dB or about 90 times.
    [Show full text]
  • Basic DC Motor Circuits
    Basic DC Motor Circuits Living with the Lab Gerald Recktenwald Portland State University [email protected] DC Motor Learning Objectives • Explain the role of a snubber diode • Describe how PWM controls DC motor speed • Implement a transistor circuit and Arduino program for PWM control of the DC motor • Use a potentiometer as input to a program that controls fan speed LWTL: DC Motor 2 What is a snubber diode and why should I care? Simplest DC Motor Circuit Connect the motor to a DC power supply Switch open Switch closed +5V +5V I LWTL: DC Motor 4 Current continues after switch is opened Opening the switch does not immediately stop current in the motor windings. +5V – Inductive behavior of the I motor causes current to + continue to flow when the switch is opened suddenly. Charge builds up on what was the negative terminal of the motor. LWTL: DC Motor 5 Reverse current Charge build-up can cause damage +5V Reverse current surge – through the voltage supply I + Arc across the switch and discharge to ground LWTL: DC Motor 6 Motor Model Simple model of a DC motor: ❖ Windings have inductance and resistance ❖ Inductor stores electrical energy in the windings ❖ We need to provide a way to safely dissipate electrical energy when the switch is opened +5V +5V I LWTL: DC Motor 7 Flyback diode or snubber diode Adding a diode in parallel with the motor provides a path for dissipation of stored energy when the switch is opened +5V – The flyback diode allows charge to dissipate + without arcing across the switch, or without flowing back to ground through the +5V voltage supply.
    [Show full text]
  • Lecture23-Amplifier Frequency Response.Pptx
    EE105 – Fall 2014 Microelectronic Devices and Circuits Prof. Ming C. Wu [email protected] 511 Sutardja Dai Hall (SDH) Lecture23-Amplifier Frequency Response 1 Common-Emitter Amplifier – ωH Open-Circuit Time Constant (OCTC) Method At high frequencies, impedances of coupling and bypass capacitors are small enough to be considered short circuits. Open-circuit time constants associated with impedances of device capacitances are considered instead. 1 ωH ≅ m ∑RioCi i=1 where Rio is resistance at terminals of ith capacitor C with all other v ! R $ i R = x = r #1+ g R + L & capacitors open-circuited. µ 0 π 0 m L ix " rπ 0 % For a C-E amplifier, assuming C = 0 L 1 1 ωH ≅ = Rπ 0 = rπ 0 Rπ 0Cπ + Rµ 0Cµ rπ 0CT Lecture23-Amplifier Frequency Response 2 1 Common-Emitter Amplifier High Frequency Response - Miller Effect • First, find the simplified small -signal model of the C-E amp. • Replace coupling and bypass capacitors with short circuits • Insert the high frequency small -signal model for the transistor ! # rπ 0 = rπ "rx +(RB RI )$ Lecture23-Amplifier Frequency Response 3 Common-Emitter Amplifier – ωH High Frequency Response - Miller Effect (cont.) v R r Input gain is found as A = b = in ⋅ π i v R R r r i I + in x + π R || R || (r + r ) r = 1 2 x π ⋅ π RI + R1 || R2 || (rx + rπ ) rx + rπ Terminal gain is vc Abc = = −gm (ro || RC || R3 ) ≅ −gm RL vb Using the Miller effect, we find CeqB = Cµ (1− Abc )+Cπ (1− Abe ) the equivalent capacitance at the base as: = Cµ (1−[−gm RL ])+Cπ (1− 0) = Cµ (1+ gm RL )+Cπ Chap 17-4 Lecture23-Amplifier Frequency Response 4 2 Common-Emitter Amplifier – ωH High Frequency Response - Miller Effect (cont.) ! # • The total equivalent resistance ReqB = rπ 0 = rπ "rx +(RB RI )$ at the base is • The total capacitance and CeqC = Cµ +CL resistance at the collector are ReqC = ro RC R3 = RL • Because of interaction through 1 ω = Cµ, the two RC time constants p1 ! # rπ 0 "Cπ +Cµ (1+ gm RL )$+ RL (Cµ +CL ) interact, giving rise to a dominant pole.
    [Show full text]
  • INA106: Precision Gain = 10 Differential Amplifier Datasheet
    INA106 IN A1 06 IN A106 SBOS152A – AUGUST 1987 – REVISED OCTOBER 2003 Precision Gain = 10 DIFFERENTIAL AMPLIFIER FEATURES APPLICATIONS ● ACCURATE GAIN: ±0.025% max ● G = 10 DIFFERENTIAL AMPLIFIER ● HIGH COMMON-MODE REJECTION: 86dB min ● G = +10 AMPLIFIER ● NONLINEARITY: 0.001% max ● G = –10 AMPLIFIER ● EASY TO USE ● G = +11 AMPLIFIER ● PLASTIC 8-PIN DIP, SO-8 SOIC ● INSTRUMENTATION AMPLIFIER PACKAGES DESCRIPTION R1 R2 10kΩ 100kΩ 2 5 The INA106 is a monolithic Gain = 10 differential amplifier –In Sense consisting of a precision op amp and on-chip metal film 7 resistors. The resistors are laser trimmed for accurate gain V+ and high common-mode rejection. Excellent TCR tracking 6 of the resistors maintains gain accuracy and common-mode Output rejection over temperature. 4 V– The differential amplifier is the foundation of many com- R3 R4 10kΩ 100kΩ monly used circuits. The INA106 provides this precision 3 1 circuit function without using an expensive resistor network. +In Reference The INA106 is available in 8-pin plastic DIP and SO-8 surface-mount packages. Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Copyright © 1987-2003, Texas Instruments Incorporated Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. www.ti.com SPECIFICATIONS ELECTRICAL ° ± At +25 C, VS = 15V, unless otherwise specified.
    [Show full text]
  • Lecture 19 Common-Gate Stage
    4/7/2008 Lecture 19 OUTLINE • Common‐gate stage • Source follower • Reading: Chap. 7.3‐7.4 EE105 Spring 2008 Lecture 19, Slide 1Prof. Wu, UC Berkeley Common‐Gate Stage AvmD= gR • Common‐gate stage is similar to common‐base stage: a rise in input causes a rise in output. So the gain is positive. EE105 Spring 2008 Lecture 19, Slide 2Prof. Wu, UC Berkeley EE105 Fall 2007 1 4/7/2008 Signal Levels in CG Stage • In order to maintain M1 in saturation, the signal swing at Vout cannot fall below Vb‐VTH EE105 Spring 2008 Lecture 19, Slide 3Prof. Wu, UC Berkeley I/O Impedances of CG Stage 1 R = in λ =0 RRout= D gm • The input and output impedances of CG stage are similar to those of CB stage. EE105 Spring 2008 Lecture 19, Slide 4Prof. Wu, UC Berkeley EE105 Fall 2007 2 4/7/2008 CG Stage with Source Resistance 1 g vv= m Xin1 + RS gm 1 vv g AgR==out x m vmD1 vvxin + RS gm R gR ==D mD 1 1+ gRmS + RS gm • When a source resistance is present, the voltage gain is equal to that of a CS stage with degeneration, only positive. EE105 Spring 2008 Lecture 19, Slide 5Prof. Wu, UC Berkeley Generalized CG Behavior Rgout= (1++g mrR O) S r O • When a gate resistance is present it does not affect the gain and I/O impedances since there is no potential drop across it (at low frequencies). • The output impedance of a CG stage with source resistance is identical to that of CS stage with degeneration.
    [Show full text]
  • Transistor Basics
    Transistor Basics: Collector The schematic representation of a transistor is shown to the left. Note the arrow pointing down towards the emitter. This signifies it's an NPN transistor (current flows in the direction of the arrow). See the Q1 datasheet at: www.fairchildsemi.com. Base 2N3904 A transistor is basically a current amplifier. Say we let 1mA flow into the base. We may get 100mA flowing into the collector. Note: The Emitter currents flowing into the base and collector exit through the emitter (the sum off all currents entering or leaving a node must equal zero). The gain of the transistor will be listed in the datasheet as either βDC or Hfe. The gain won't be identical even in transistors with the same part number. The gain also varies with the collector current and temperature. Because of this we will add a safety margin to all our base current calculations (i.e. if we think we need 2mA to turn on the switch we'll use 4mA just to make sure). Sample circuit and calculations (NPN transistor): Let's say we want to heat a block of metal. One way to do that is to connect a power resistor to the block and run current through the resistor. The resistor heats up and transfers some of the heat to the block of metal. We will use a transistor as a switch to control when the resistor is heating up and when it's cooling off (i.e. no current flowing in the resistor). In the circuit below R1 is the power resistor that is connected to the object to be heated.
    [Show full text]
  • The Transistor, Fundamental Component of Integrated Circuits
    D The transistor, fundamental component of integrated circuits he first transistor was made in (SiO2), which serves as an insulator. The transistor, a name derived from Tgermanium by John Bardeen and In 1958, Jack Kilby invented the inte- transfer and resistor, is a fundamen- Walter H. Brattain, in December 1947. grated circuit by manufacturing 5 com- tal component of microelectronic inte- The year after, along with William B. ponents on the same substrate. The grated circuits, and is set to remain Shockley at Bell Laboratories, they 1970s saw the advent of the first micro- so with the necessary changes at the developed the bipolar transistor and processor, produced by Intel and incor- nanoelectronics scale: also well-sui- the associated theory. During the porating 2,250 transistors, and the first ted to amplification, among other func- 1950s, transistors were made with sili- memory. The complexity of integrated tions, it performs one essential basic con (Si), which to this day remains the circuits has grown exponentially (dou- function which is to open or close a most widely-used semiconductor due bling every 2 to 3 years according to current as required, like a switching to the exceptional quality of the inter- “Moore's law”) as transistors continue device (Figure). Its basic working prin- face created by silicon and silicon oxide to become increasingly miniaturized. ciple therefore applies directly to pro- cessing binary code (0, the current is blocked, 1 it goes through) in logic cir- control gate cuits (inverters, gates, adders, and memory cells). The transistor, which is based on the switch source drain transport of electrons in a solid and not in a vacuum, as in the electron gate tubes of the old triodes, comprises three electrodes (anode, cathode and gate), two of which serve as an elec- transistor source drain tron reservoir: the source, which acts as the emitter filament of an electron gate insulator tube, the drain, which acts as the col- source lector plate, with the gate as “control- gate drain ler”.
    [Show full text]