I am designing a folded cascode OTA for pipelined ADC. It requires 400M Hz GBW with lowest power consumption. the load capacitance is fixed (i.e. 4 pF), so i need to design the input MOST to get the largest gm under the lowest id of the input MOST.
as we know, gm is inversely propotional to (Vgs-Vth), the question is: what is the proper Vgs-Vth?
i designed the mosts and simulation result is:
#(0.18um process) the simulation tool is Spectre.#
w=300u, L=0.18u, Id=1.023mA, Vgs=558mV, Vth=470mV, Vdsat=118mV, Vds=1.187mV, gm=14.6mS, ron=1.16K
is this value (Vgs-Vth=88mV) proper? would it course some problems in reality? or can i still decrease the Vgs for more larger gm? what is the proper value in reality?
Would you give me some hints? Thank you in advance!