Electronics II Essentials

By The Editors of REA

REA’s Essentials provide quick and easy access to critical information in a variety of different fields, ranging from the most basic to the most advanced. As its name implies, these concise, comprehensive study guides summarize the essentials of the field covered. Essentials are helpful when preparing for exams, doing homework and will remain a lasting reference source for students, teachers, and professionals. Electronics II covers operational amplifiers, feedback and frequency compensation of OP amps, multivibrators, logic gates and families, Boolean algebra, registers, counters, arithmetic units, oscillators, radio-frequency circuits, flip-flops, and waveshaping and waveform generators.

• Language: English
• Publisher: Research & Education Association
• Release date: Jan 1, 2013
• ISBN: 9780738672229

Book preview

GENERATORS

CHAPTER 10

OPERATIONAL AMPLIFIERS

10.1 THE BASIC OPERATIONAL AMPLIFIER

Ideal op amp:

Ri = ∞

Ro = 0

Av = –∞

B.W. = ∞

Vo = 0 when V1 = V2, independent of the magnitude of V1

no drift of characteristics

Ideal op amp with feedback impedances

This is the basic inverting circuit. This topology represents voltage-shunt feedback.

Inverting operational amplifier:

Small signal model

For a small-signal model, |Av| ≠ ∞, Ri ≠ ∞ and Ro ≠ 0.

(where the y’s are the admittances)

Non-inverting op amp:

The configuration is that of a voltage-series feedback amplifier, with the feedback voltage, vf, equal to v2.

The feedback factor

If Av β >> 1, then

Configuration:

10.2 OFFSET ERROR VOLTAGES AND CURRENTS

Input bias currents IB1 and IB2 and offset voltage Vio.

The input offset current is the difference between the input currents entering the input terminals of a balanced amplifier. In the figure above,

(when Vo = 0)

, where

ΔVio = the change of input offset voltage

and

ΔT = change in temperature.

Input offset voltage − When applied to the input terminals, this voltage will balance the amplifier.

Input offset voltage drift:

ΔVio = change of input offset voltage.

Output offset voltage − This voltage marks the difference between the dc voltages measured at the output terminals on grounding the two input terminals.

Input common mode range − This is the range of the common mode input signal for which the differential amplifier remains linear.

Input differential range − This range is the maximum difference signal that can safely be applied to the op amp input terminals.

Output voltage range − This is the maximum output swing that can be obtained without significant distortion at a specified load resistance.

Full-power bandwidth − This bandwidth is the maximum frequency at which a sinusoid whose size is the output voltage range is obtained.

Slew rate − This is the time rate of change of the closed-loop amplifier output voltage under large signal conditions.

The model of an op amp and balancing techniques:

Model:

Universal balancing technique:

It is necessary to apply a small dc voltage in the input to bring the d output voltage to zero.

The following circuit supplies a small voltage in a series