Question

Consider an ideal inverting op-amp circuit as shown in the figure below:

$\text{Both the resistance}{R}_1\text{and}{R}_2\text{are constructed with a tolerance of 5\%, then the range in which the gain of the amplifier can approximately vary is}$

• A. $-8<G_v<-10$
• B. $-8<G_v<-11$
• C. $-9<G_v<-10$
• D. $-9<G_v<-11$

Answer 1

The correct option is D $-9<G_v<-11$

$\text{Gain}=\frac{R_L}{R_1}=\frac{-R_2(1\pm x\%)}{R_1(1\pm x\%)}$
$\therefore G_{\text{max}}=\frac{-R_2(1\pm x\%)}{R_1(1\pm x\%)}=\frac{-R_2(1+\frac{5}{100})}{R_1(1-\frac{5}{100})}$
$=\frac{-100(1+0.05}{10(1-0.05)}=-10\times \frac{1.05}{0.95}\approx -11\text{V/V}$

$\therefore G_{\text{min}}=\frac{-R_L(1-\frac{5}{100})}{R_1(1+\frac{5}{100})}=-10\times \frac{0.95}{1.05}\approx -9\text{V/V}$