Re: Diff Amp with active load vs diff amp with linear resist
For resistive loaded differential amplfiers, gain will be gm*Rl, which requires high values of Rl to achieve moderate gain .However, these resistors will consume a voltage drop of Rl*Io/2 which would lead to a very limited headroom and would drive your transistors quickly out of saturation ,besides they consume lots of chip area .
So, for higher gains ,using active loads is more convenient .For active loads implementation, you can either use current sources at loads (MOS transistors each with a constant Vgs and none is diode connected) and in this case you'll need to have a CMFB network (Common Mode Feedback network) which is not easy to design .Or, you can use a current mirror at the load (single ended or unbalanced amplifier) and in this case your o/p will be single ended and more sensitive to Common Mode variation even in the case of perfect matching .