1.8V Single stage opamp

Gain = 18763 Notice when calculate gain, Vp2p=0.04mV The output is clipped at upper Vdd If you decrease Q3 and Q4 dc offset, there is no use because they only determine wheter Q3 and Q4 goes to triode, but won't affect dc value of Vout. Instead, dc value of Vout is determined by Vsg of Q2 and Q1, decrease W/L of Q2 and Q1 can increase Vsg, thus shift down Vout, but notice if ac output swing beyond Vdd-(Vsg-Vth), Q1 goes to triode, notice decrease W/L to shift down Vout can't solve this problem as maximum Vov decreases as Vsg increases, i.e. Q1 still saturate even Vout shift down Here Q1 saturate beyond 1.8-(1.1-0.4) = 1.1V, so you can see the gain decreases beyond this value