Linear Amplifier Basics; Biasing
Total Page：16
File Type：pdf, Size：1020Kb
Load more
Recommended publications
-
Valve Biasing
VALVE AMP BIASING Biased information How have valve amps survived over 30 years of change? Derek Rocco explains why they are still a vital ingredient in music making, and talks you through the mysteries of biasing N THE LAST DECADE WE HAVE a signal to the grid it causes a water as an electrical current, you alter the negative grid voltage by seen huge advances in current to flow from the cathode to will never be confused again. When replacing the resistor I technology which have the plate. The grid is also known as your tap is turned off you get no to gain the current draw required. profoundly changed the way we the control grid, as by varying the water flowing through. With your Cathode bias amplifiers have work. Despite the rise in voltage on the grid you can control amp if you have too much negative become very sought after. They solid-state and digital modelling how much current is passed from voltage on the grid you will stop have a sweet organic sound that technology, virtually every high- the cathode to the plate. This is the electrical current from flowing. has a rich harmonic sustain and profile guitarist and even recording known as the grid bias of your amp This is known as they produce a powerful studios still rely on good ol’ – the correct bias level is vital to the ’over-biased’ soundstage. Examples of these fashioned valves. operation and tone of the amplifier. and the amp are most of the original 1950’s By varying the negative grid will produce Fender tweed amps such as the What is a valve? bias the technician can correctly an unbearable Deluxe and, of course, the Hopefully, a brief explanation will set up your amp for maximum distortion at all legendary Vox AC30. -
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. -
HF Linear Amplifiers
- • - • --• --•• • •••- • --••• - • ••• •- • HFHF LinearLinear AmplifiersAmplifiers Basic amplifier concepts, types & operation Adam Farson VA7OJ Tube Amplifiers Solid-State Amplifiers 1 October 2005 NSARC HF Operators – HF Amplifiers 1 BasicBasic LinearLinear AmplifierAmplifier RequirementsRequirements - • - • --• --•• • •••- • --••• - • ••• •- • ! Amplify the exciter’s RF output (by 10 dB or more). ! Provide a means of correct matching to load. ! Amplify complex signals such as SSB with minimum distortion (maximum linearity). ! Transmit a spectrally-pure signal. ! Assure a safe operating environment. 1 October 2005 NSARC HF Operators – HF Amplifiers 2 BasicBasic AmplifierAmplifier TypesTypes - • - • --• --•• • •••- • --••• - • ••• •- • ! Tube, grounded-grid triode (cathode-driven) – most popular. Some designs use tetrodes. ! Tube, grounded-cathode tetrode (grid-driven) – less common, but growing in popularity. ! Solid-state, BJT (junction transistors) – 500W or 1 kW. ! Solid-state, MOSFET – typically 1 kW. 1 October 2005 NSARC HF Operators – HF Amplifiers 3 Grounded-Grid Triode Amplifier showing pi-section input & output networks - • - • --• --•• • •••- • --••• - • ••• •- • Input network: C1-L1-C2 Plate feed circuit: RFC2-C5 Output network: C6-L2-C7 Plate tuning: C6 Loading: C7 Input impedance of grounded-grid triode amplifier Is low, complex, and also non-linear (decreases at onset of grid current). Tuned input network tunes out reactive (C) component, and also linearizes tube input impedance via flywheel effect. Cathode choke RFC1 provides DC return path for plate feed, and allows cathode to “float” at RF potential. Heater (or filament of directly-heated tube) powered via bifilar RF choke. Pi-output network matches tube load resistance to antenna, RF drive power added to output. Amplifier can operate in Class AB1 (no grid current) or AB2 (some grid current). 1 October 2005 NSARC HF Operators – HF Amplifiers 4 TubesTubes forfor GroundedGrounded--GridGrid AmplifiersAmplifiers - • - • --• --•• • •••- • --••• - • ••• •- • • Directly-heated glass triode (e.g. -
High Efficiency Power Amplifier for High Frequency Radio Transmitters
High Efficiency Power Amplifier for High Frequency Radio Transmitters M.Vasic, 0. Garcia, J.A. Oliver, P. Alou, D. Diaz, J.A. A.Gimeno, J.M.Pardo, C.Benavente, F.J.Ortega Cobos Radio Engineering Group (GIRA) Centra de Electronica Industrial (CEI) Universidad Politecnica de Madrid Universidad Politecnica de Madrid Madrid, Spain Madrid, Spain [email protected] Abstract— Modern transmitters usually have to amplify and One of the techniques that offer high efficiency and high transmit complex communication signals with simultaneous linearity is the Kahn's technique or Envelope Elimination and envelope and phase modulation. Due to this property of the Restoration (EER) technique [3]. This method proposes transmitted signal, linear power amplifiers (class A, B or AB) linearization of highly efficient, but nonlinear power amplifier are usually employed as a solution for the power amplifier stage. (class E or D) by modulation of its supply voltage. The These amplifiers have high linearity, but suffer from low modulation of the supply voltage is done through an envelope efficiency when the transmitted signal has high peak-to-average amplifier according to the reference signal that is proportional power ratio. The Kahn envelope elimination and restoration (EER) technique is used to enhance efficiency of RF to the envelope of the transmitted signal, while the phase transmitters, by combining highly efficient, nonlinear RF modulation of the transmitted signal is conducted through the amplifier (class D or E) with a highly efficient envelope amplifier nonlinear amplifier. The basis for EER is the equivalence of in order to obtain linear and highly efficient RF amplifier. -
Bias Circuits for RF Devices
Bias Circuits for RF Devices Iulian Rosu, YO3DAC / VA3IUL, http://www.qsl.net/va3iul A lot of RF schematics mention: “bias circuit not shown”; when actually one of the most critical yet often overlooked aspects in any RF circuit design is the bias network. The bias network determines the amplifier performance over temperature as well as RF drive. The DC bias condition of the RF transistors is usually established independently of the RF design. Power efficiency, stability, noise, thermal runway, and ease to use are the main concerns when selecting a bias configuration. A transistor amplifier must possess a DC biasing circuit for a couple of reasons. • We would require two separate voltage supplies to furnish the desired class of bias for both the emitter-collector and the emitter-base voltages. • This is in fact still done in certain applications, but biasing was invented so that these separate voltages could be obtained from but a single supply. • Transistors are remarkably temperature sensitive, inviting a condition called thermal runaway. Thermal runaway will rapidly destroy a bipolar transistor, as collector current quickly and uncontrollably increases to damaging levels as the temperature rises, unless the amplifier is temperature stabilized to nullify this effect. Amplifier Bias Classes of Operation Special classes of amplifier bias levels are utilized to achieve different objectives, each with its own distinct advantages and disadvantages. The most prevalent classes of bias operation are Class A, AB, B, and C. All of these classes use circuit components to bias the transistor at a different DC operating current, or “ICQ”. When a BJT does not have an A.C. -
First-Order Circuits
CHAPTER SIX FIRST-ORDER CIRCUITS Chapters 2 to 5 have been devoted exclusively to circuits made of resistors and independent sources. The resistors may contain two or more terminals and may be linear or nonlinear, time-varying or time-invariant. We have shown that these resistive circuits are always governed by algebraic equations. In this chapter, we introduce two new circuit elements, namely, two- terminal capacitors and inductors. We will see that these elements differ from resistors in a fundamental way: They are lossless, and therefore energy is not dissipated but merely stored in these elements. A circuit is said to be dynamic if it includes some capacitor(s) or some inductor(s) or both. In general, dynamic circuits are governed by differential equations. In this initial chapter on dynamic circuits, we consider the simplest subclass described by only one first-order differential equation-hence the name first-order circuits. They include all circuits containing one 2-terminal capacitor (or inductor), plus resistors and independent sources. The important concepts of initial state, equilibrium state, and time constant allow us to find the solution of any first-order linear time-invariant circuit driven by dc sources by inspection (Sec. 3.1). Students should master this material before plunging into the following sections where the inspection method is extended to include linear switching circuits in Sec. 4 and piecewise- linear circuits in Sec. 5. Here,-the important concept of a dynamic route plays a crucial role in the analysis of piecewise-linear circuits by inspection. l TWO-TERMINAL CAPACITORS AND INDUCTORS Many devices cannot be modeled accurately using only resistors. -
Basic Electrical Engineering
BASIC ELECTRICAL ENGINEERING V.HimaBindu V.V.S Madhuri Chandrashekar.D GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING AND TECHNOLOGY (Autonomous) Index: 1. Syllabus……………………………………………….……….. .1 2. Ohm’s Law………………………………………….…………..3 3. KVL,KCL…………………………………………….……….. .4 4. Nodes,Branches& Loops…………………….……….………. 5 5. Series elements & Voltage Division………..………….……….6 6. Parallel elements & Current Division……………….………...7 7. Star-Delta transformation…………………………….………..8 8. Independent Sources …………………………………..……….9 9. Dependent sources……………………………………………12 10. Source Transformation:…………………………………….…13 11. Review of Complex Number…………………………………..16 12. Phasor Representation:………………….…………………….19 13. Phasor Relationship with a pure resistance……………..……23 14. Phasor Relationship with a pure inductance………………....24 15. Phasor Relationship with a pure capacitance………..……….25 16. Series and Parallel combinations of Inductors………….……30 17. Series and parallel connection of capacitors……………...…..32 18. Mesh Analysis…………………………………………………..34 19. Nodal Analysis……………………………………………….…37 20. Average, RMS values……………….……………………….....43 21. R-L Series Circuit……………………………………………...47 22. R-C Series circuit……………………………………………....50 23. R-L-C Series circuit…………………………………………....53 24. Real, reactive & Apparent Power…………………………….56 25. Power triangle……………………………………………….....61 26. Series Resonance……………………………………………….66 27. Parallel Resonance……………………………………………..69 28. Thevenin’s Theorem…………………………………………...72 29. Norton’s Theorem……………………………………………...75 30. Superposition Theorem………………………………………..79 31. -
Chapter 4 BJT BIASING CIRCUIT Introduction – Biasing the Analysis Or Design of a Transistor Amplifier Requires Knowledge of Both the Dc and Ac Response of the System
Chapter 4 BJT BIASING CIRCUIT Introduction – Biasing The analysis or design of a transistor amplifier requires knowledge of both the dc and ac response of the system. In fact, the amplifier increases the strength of a weak signal by transferring the energy from the applied DC source to the weak input ac signal The analysis or design of any electronic amplifier therefore has two components: •The dc portion and •The ac portion During the design stage, the choice of parameters for the required dc levels will affect the ac response. What is biasing circuit? Biasing: Application of dc voltages to establish a fixed level of current and voltage. Purpose of the DC biasing circuit • To turn the device “ON” • To place it in operation in the region of its characteristic where the device operates most linearly . •Proper biasing circuit which it operate in linear region and circuit have centered Q-point or midpoint biased •Improper biasing cause Improper biasing cause •Distortion in the output signal •Produce limited or clipped at output signal Important basic relationship IECB= II + I β = C I B IE =+≅ (β 1) IIBC VVVCB= CE − BE Operating Point •Active or Linear Region Operation Base – Emitter junction is forward biased Base – Collector junction is reverse biased Good operating point •Saturation Region Operation Base – Emitter junction is forward biased Base – Collector junction is forward biased •Cutoff Region Operation Base – Emitter junction is reverse biased BJT Analysis DC AC analysis analysis Calculate gains of the Calculate the DC Q-point amplifier -
Class D Audio Amplifier Basics
Application Note AN-1071 Class D Audio Amplifier Basics By Jun Honda & Jonathan Adams Table of Contents Page What is a Class D Audio Amplifier? – Theory of Operation..................2 Topology Comparison – Linear vs. Class D .........................................4 Analogy to a Synchronous Buck Converter..........................................5 Power Losses in the MOSFETs ...........................................................6 Half Bridge vs. Full Bridge....................................................................7 Major Cause of Imperfection ................................................................8 THD and Dead Time ............................................................................9 Audio Performance Measurement........................................................10 Shoot Through and Dead Time ............................................................11 Power Supply Pumping........................................................................12 EMI Consideration: Qrr in Body Diode .................................................13 Conclusion ...........................................................................................14 A Class D audio amplifier is basically a switching amplifier or PWM amplifier. There are a number of different classes of amplifiers. This application note takes a look at the definitions for the main classifications. www.irf.com AN-1071 1 AN-1071 What is a Class D Audio Amplifier - non-linearity of Class B designs is overcome, Theory of Operation without the inefficiencies -
Eimac Care and Feeding of Tubes Part 3
SECTION 3 ELECTRICAL DESIGN CONSIDERATIONS 3.1 CLASS OF OPERATION Most power grid tubes used in AF or RF amplifiers can be operated over a wide range of grid bias voltage (or in the case of grounded grid configuration, cathode bias voltage) as determined by specific performance requirements such as gain, linearity and efficiency. Changes in the bias voltage will vary the conduction angle (that being the portion of the 360° cycle of varying anode voltage during which anode current flows.) A useful system has been developed that identifies several common conditions of bias voltage (and resulting anode current conduction angle). The classifications thus assigned allow one to easily differentiate between the various operating conditions. Class A is generally considered to define a conduction angle of 360°, class B is a conduction angle of 180°, with class C less than 180° conduction angle. Class AB defines operation in the range between 180° and 360° of conduction. This class is further defined by using subscripts 1 and 2. Class AB1 has no grid current flow and class AB2 has some grid current flow during the anode conduction angle. Example Class AB2 operation - denotes an anode current conduction angle of 180° to 360° degrees and that grid current is flowing. The class of operation has nothing to do with whether a tube is grid- driven or cathode-driven. The magnitude of the grid bias voltage establishes the class of operation; the amount of drive voltage applied to the tube determines the actual conduction angle. The anode current conduction angle will determine to a great extent the overall anode efficiency. -
Chapter 2: Kirchhoff Law and the Thvenin Theorem
Chapter 3: Capacitors, Inductors, and Complex Impedance Chapter 3: Capacitors, Inductors, and Complex Impedance In this chapter we introduce the concept of complex resistance, or impedance, by studying two reactive circuit elements, the capacitor and the inductor. We will study capacitors and inductors using differential equations and Fourier analysis and from these derive their impedance. Capacitors and inductors are used primarily in circuits involving time-dependent voltages and currents, such as AC circuits. I. AC Voltages and circuits Most electronic circuits involve time-dependent voltages and currents. An important class of time-dependent signal is the sinusoidal voltage (or current), also known as an AC signal (Alternating Current). Kirchhoff’s laws and Ohm’s law still apply (they always apply), but one must be careful to differentiate between time-averaged and instantaneous quantities. An AC voltage (or signal) is of the form: V(t) =Vp cos(ωt) (3.1) where ω is the angular frequency, Vp is the amplitude of the waveform or the peak voltage and t is the time. The angular frequency is related to the freguency (f) by ω=2πf and the period (T) is related to the frequency by T=1/f. Other useful voltages are also commonly defined. They include the peak-to-peak voltage (Vpp) which is twice the amplitude and the RMS voltage (VRMS) which is VVRMS = p / 2 . Average power in a resistive AC device is computed using RMS quantities: P=IRMSVRMS = IpVp/2. (3.2) This is important enough that voltmeters and ammeters in AC mode actually return the RMS values for current and voltage. -
Linear Electronic Circuits and Systems Graham Bishop Beginning Basic P.E
Linear Electronic Circuits andSystems Macmillan Basis Books in Electronics General Editor Noel M. Morris, Principal Lecturer, North Staffordshire Polytechnic Linear Electronic Circuits and Systems Graham Bishop Beginning Basic P.E. Gosling Continuing Basic P.E.Gosling Microprocessors and Microcomputers Eric Huggins Digital Electronic Circuits and Systems Noel M. Morris Electrical Circuits and Systems Noel M. Morris Microprocessor and Microcomputer Technology Noel M. Morris Semiconductor Devices Noel M. Morris Other related books Electrical and Electronic Systems and Practice Graham Bishop Electronics for Technicians Graham Bishop Digital Techniques Noel M. Morris Electrical Principles Noel M. Morris Essential Formulae for Electronic and Electrical Engineers: New Pocket Book Format Noel M. Morris Mastering Electronics John Watson Linear Electronic Circuits andSystems SECOND EDITION Graham Bishop Vice Principal Bridgwater College M MACMI LLAN PRESS LONDON © G. D. Bishop 1974, 1983 All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, without permission First edition 1974 Second edition 1983 Published by THE MACMILLAN PRESS LTD London and Basingstoke Companies and representatives throughout the world ISBN 978-0-333-35858-0 ISBN 978-1-349-06914-9 (eBook) DOI 10.1007/978-1-349-06914-9 Contents Foreword viii Preface to the First Edition ix Preface to the Second Edition xi 1 Signal processing 1 1.1 Voltages and currents 1 1.2 Transient responses 4 1.3 R-L-C transients 6 1.4 The d.c. restorer