Topic: Analog Circuits
For the circuit shown below if $g_m = 3 \times 10^{-3}$ and $R_s = 3000~\Omega$, then the approximate value of $R_o$ is
- A. 3000 $\Omega$
- B. 1000/3 $\Omega$
- C. 300 $\Omega$
- D. 100 $\Omega$
Answer: C. 300 $\Omega$
Explanation: $r_d = \frac{1}{g_m} = \frac{1000}{3} \Omega$\n$R_o = r_d || R_s = \frac{\frac{1000}{3} \times 3000}{\frac{1000}{3} + 3000} = \frac{1000 \times 3000}{3} \times \frac{3}{10000} = 300~\Omega$