Question

In a voltage series feedback network the open loop gain A = - 100, $R_i=10k\Omega and{R}_0=20k\Omega$. If feedback factor $\beta$ is -0.1, then $Z_{if}and{Z}_{0f}$ respectively are

• A. $122k\Omega and1.64k\Omega$
• B. $1.64k\Omega and122k\Omega$
• C. $110k\Omega and1.82k\Omega$
• D. $1.82k\Omega and110k\Omega$

Answer 1

The correct option is C $110k\Omega and1.82k\Omega$

$Z_{if}=Z_i(1+\beta A)$
$=10k(1+(-0.1)\times (-100\left)\right)=110k\Omega$

$Z_{0f}=\frac{Z_0}{1+\beta A}=\frac{20\times {10}^3}{1+(-0.1\times -100)}$

$=1.82k\Omega$