I am designing the circuit shown in the figure below, In my first design I didn't use the source floower transistors MT1 and MT2, thus I gout a high current at the output stage (1.3mA). It was explaned by Allen holberg that the use of the source follower is to shift the dc level to the output stage so VSG6= VSD4, comparing without using the source follower VSG6= VSD4+VSD4C... this mean that the source follower shifted the value by the amount of VSD4C... it is illustrated in the graph as well.
my question, how we design the source follower in this circuit to get shift by that value, up to my knowledge that the shift of the source amplifier is equal to VSD+Vth.
So please help me on designing the aspect ratio of the source follower that satisfy this condition
Why? The center voltage vo1 should be around VDD/2 (to achieve high swing), so you need that high shift 'cause VSG6 shouldn't get too much overdrive voltage. You can adjust Id6 by its W/L(6) ratio - I think this is meant by the Id6 vs. VSG6 diagram.