Operational Amplifier Applications Part 2-Analogue Integerated Electronics-Lecture Slides, Slides of Analog Electronics

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EE 4623: Analog Integrated Electronics^ Operational Amplifier Applications

Objectives

Students should be able to:^ ^ Explain basic amplifier terms including:^ ^ Gain, Linear, Distortion, Decibel, Saturation, Biasing, Models, Cascade,Coupling Capacitor,

Transconductance, Open- and Closed-Circuit Models. ^ Calculate gains for amplifier configurations. ^ Understand tradeoffs inherent in amplifier designs. ^ Identify the four amplifier types. ^ Understand how frequency response relates to amplifiers. ^ Analyze op-amp simple circuits and effect of a finite open-loopgain. ^ Understand the effects of offset voltage and offset current in anOp-Amp.

Amplifier Gain in Decibels  Amplifier gain is expressed in decibels (dB)  Originally it was expressed as “Bels” (named after Alexander GrahamBell), but these proved to be of insufficient size so we multiply “Bels”by 10^ ^ “decibels.”  Decibels are a log-based ratio and are therefore

dimensionless. ^ Purpose:^ We want to measure the ratio of some value relative toanother (e.g. sound power in a stereo amplifier). ^ Derivation of dB…

Derivation of Decibels  Ratio of power of interest (call it “

p ”) to some other reference^1 power (say,^ p ):^2  However, these values are generally quite huge and tend to belogarithmically related; thus, creation of “the Bel:”

p^1 p^2 p^1 log^ Bel  p^2

In-Class Exercise: dB for Voltage  Given the following equation for expressing power indecibels, write a similar equation expressing

voltage^ in decibels:

1 10 log^2

power

p

decibel^

 p

dB for Voltage ^ First, let’s relate voltage to power:

p^ vi^  / i v^ r^ ^2 p v^ r 

Let’s Draw some Physical Conclusions ^ if dB is positive, then

v> v ,^ ^ the signal is amplified.^1 ^ if dB is negative, then

v< v ,^ ^ the signal is attenuated.^1 ^ if dB is 0, then^ v

= v. 1 2

Signal Amplification  “A” is the amplifier^ gain.  The premise is that this is a^ linear

amplifier. ^ Amplifiers that are not linear exhibit

nonlinear distortion

. )()( tAvt v^  io^

The Meaning of “Active” in EE What makes an amplifier an^ active

circuit component? ^ Active components are devices that “add intelligence” in some way to a signal thatpasses through it (in contrast to passive components which consume – but do notproduce – energy). Passive components are

incapable^ of power gain. ^ Active components can also

switch^ the flow of current and are capable of

gain.

Examples:^ Transistors, diodes, and vacuum tubes.

Amplifier Saturation  What is the range of^ v? I  L and L are the positive, and negative + – (^) saturation levels , respectively.  In order to avoid output saturation, theinput must be kept within^ the linearrange of operation: L L   v   I A Av v

Biasing ^ The bias point is also referred to asthe…^ ^ quiescent point (Q-point).^ ^ DC bias point.^ ^ operating point. ^ The time-varying input signal

v ( t )^ is i^ superimposed on the DC biasvoltage^ V to create the total I^ instantaneous input,

v ( t )^ ^ ( ) I^

( ) v t V^ v t ^  I I^ i

Coupling Capacitors ^ You will be using

coupling capacitors

rather heavily so it is good to get an idea about what they are accomplishing!

Closed- and Open-Circuit Amplifiers

Open-Circuit Amplifier Model  What is the relationship of^ v to^ o^

v in the^ open-circuit i^

voltage amplifier model? Here,^ R accounts for the fact that the amp draws an input current ( i^

i^ ) from ______. i R accounts for changes in output voltage as the amp is called on to supply output o^ current ( i ) to _____. o  A is the “open-circuit” (voltage) gain factor (i.e., it is the gain of the vo^

unloaded amplifier)