0195136047.pdf

5.3 PRACTICAL PROPERTIES OF OPERATIONAL AMPLIFIERS 243

Solution

vo=Vmsinωt

dvo

dt

=ωVm cosωt

slew rate=maximum value of

dvo

dt

=ωVm=

0. 5

10 −^6

Hence,

ω=

0. 5

1. 5 × 10 −^6

or f=53 kHz

EXAMPLE 5.3.3
Consider the op-amp circuit shown in Figure E5.3.3 and obtain expressions for the open-loop
voltage gain at (a) low and (b) high frequencies. Also determine relations for the 3-dB point
frequency and the phase shift.

Solution

Using phasors and the voltage-divider rule,

V ̄o=

(

XC

XC+Ro

)

AV ̄d, whereXC=

1

jωC

(a) At low frequencies,XCbecomes very large so thatXC>> Ro. Then,

V ̄o=AV ̄d

The output signal is in phase with the input signal, since complex voltage gainA ̄is the

same asA.

(b) At higher frequencies,XCbecomes comparable toRo. LetA ̄Fbe the complex open-loop

voltage gain at frequencyf. Then,

A ̄F=^1 /j ω C

[Ro+( 1 /j ω C )]Ao

−

+

vo

Ro

v− − v+ = vd

Avd

C

+

Figure E5.3.3