# Microelectronics NMOS amplifier

I am trying to solve a Sedra/Smith problem involving NMOS transistors. Given that both transistors are biased at the same point. Question is to find $g_{m2}, i_d, v_{d1}$ and the value of $R_D$ for which $v_o$ is pulses of amplitude 1V.

However I can't manage to find the value of the voltage pulses at the drain of $Q_1$ I actually found the solution manual for the corresponding text book, however I think that the solution is not well implemented as it suggest that the solution would be determined by: $$V_{D_1}=i_{D_1}50\Omega$$ which have no sense.

We have to find out $$\g_{m2}, i_d, v_{d1}\$$ and $$\R_D\$$.

Since $$\R_{i2} = 1/g_{m2} = 50\Omega,\$$ $$\g_{m2} = 0.02\mho\$$.

Since both transistors are biased at the same point, $$\g_{m1} = g_{m2}\$$.
$$i_d = g_{m1}v_i = 0.1\text{ mA}$$ now, $$v_{d1} = i_d\times 1/g_{m1}=i_d\times 50\Omega$$

Now the equation in solution manual makes sense. I think you can do the rest your own.

• I was actually reading about it, but, one more thing, it says that it is 0.5V (in the solutions manual), however I obtain 5mV, which one is correct?.
– Hans
May 19 '14 at 6:37
• Is it? I am also getting 5mV. What is the value of $R_D$ given in the manual? Is it $1k\Omega$? May 19 '14 at 6:41
• Well, assuming we are getting 1V at $V_O$ I obtain $10\text{-}k\Omega$ (the manual as well). I use the T-Model to explain that, I guess is the best way to do it.
– Hans
May 19 '14 at 6:51
• the same $i_d$ flows through both the transistors and hence $v_o = 0.1mA\times R_D = 1V$ or $R_D = 10k\Omega$. May 19 '14 at 7:04