amplifiers. basic amplifier concepts ideally, an amplifier produces an output signal with identical...

Amplifiers

BASIC AMPLIFIER CONCEPTS

Ideally, an amplifier produces an output signal with identical waveshape as the input signal, but with a larger amplitude.

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Inverting Amplifiers

Inverting amplifiers have negative voltage gain, and the output waveform is an inverted version of the input waveform.

Non-inverting Amplifiers

Non-inverting amplifiers have positive voltage gain amplify the input signals.

Voltage-Amplifier Model

Ri: input resistance Ro: output resistanceAvo: Open loop voltage gain ( vo / vi )

Voltage-Amplifier Model

Ri: input resistance Ro: output resistanceAvo: Open loop voltage gain ( vo / vi )

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Operational Amplifier

1. Ideal Op-Amp and its analysis2. Practical Op-Amp and its limitations3. Application of Op-Amp

IDEAL OPERATIONAL AMPLIFIERS

Power Supply Connection of Op-amp

Characteristics of Ideal Op Amp

Infinite gain for the differential input signal

Infinite input impedance

Zero output impedance

Zero gain for the common-mode input signal

Infinite bandwidth

OP-Amp Model

Ideal OP-Amp•Rin = ∞, so that it will not draw any power fromthe input signals•Rout = 0so that it will not degrade the signal due to the output resistance•Avd = ∞ it is to amplify the differential signals•Avcommon = 0 it is to reject any common mode input signalsBandwidth = ∞ so that it can be used for any signal spectrum

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Ideal op-amp rule1. No current ever flows into either input terminal. i1, i2 = 0

2. There is no voltage difference between the two input terminals v- = v+

We call this Summing Point Constraint

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v- = v+It is called ;• summing point constraint, or • virtual ground concept

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INVERTING AMPLIFIERS

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Common Mode Rejection

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An op-amp is a differential amplifier. It is desirable to rejectany signal in common to V_ and V+ terminal. In other words, Acm should be as small as possible. The quality of rejecting the common mode signal is defined byCMMR (Common mode rejection ratio)

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It is desirable for the amplifier to amplify the differenceof v1 and v2, that is 3 sin10t, and not to amplify the common component 2V.

How good the amplifier does to reject the common component is defined by the CMMR.

OP-AMP IMPERFECTIONS IN THE LINEAR RANGEOF OPERATION

Real op amps have several categories of imperfections compared to ideal op amps.

Real op amps have finite input impedance, nonzero output impedance and finite open loop gain

Ri ≠ ∞, Avo ≠ ∞, Ro ≠ 0iin ≠ 0

Bandwidth

Bandwidth = fH-fL

Idea op-amp, the bandwidth is infinity, so that signal at anyfrequency can be amplified by the amplifier.

Practical op-amp, the bandwidth is limited. That is, the gainis not uniform.

The gain at frequency higher than the fBOL is diminished graduallyat a -20dB rate of decline. The unit bandwidth product is to define how good is the frequency response of the amplifier, i. e, how wide is it bandwidth.Unity bandwidth product = Avo*fBOL

LINEAR WAVEFORM DISTORTION

If the gain of an amplifier has a different magnitude for the various frequency components of the input signal, a form of distortion known as amplitude distortion occurs. Due to bandwidth limitation.

Phase Distortion

If the phase shift of an amplifier is not proportional to frequency, phase distortion occurs.

NONLINEAR LIMITATIONS

The output voltage of a real op amp is limited to the range between certain limits that depend on the internal design of the op amp. When the output voltage tries to exceed these limits, clipping occurs.

Slew-Rate Limitation

Another nonlinear limitation of actual op-amp is that the magnitude of the rate of change of the output voltage is limited.

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DC IMPERFECTIONS