" Increasing current would look easy, but it will affect your current source's bias margin reducing CMRR. Increasing current will reduce the gain. But varying Rs will not give you a great range, but will not affect your dc operating much as it carries incremental current. "
" Increasing current would look easy, but it will affect your current source's bias margin reducing CMRR. Increasing current will reduce the gain. But varying Rs will not give you a great range, but will not affect your dc operating much as it carries incremental current. "
With a Q of 15, this circuit requires sufficiently fine tuning steps, hence the need for a coarse control (the tail currents) and a fine control (the degeneration resistance).
Now you may replace Gm2= gm6/(1+Rs*gm6)
if you increase Rs you are decreasing Gm2 so your inductor will increase.
If you increase the current source you increase Gm2 (but it has minor effect since it is source degeneration and Gm2 mostly depends on Rs). for higher gm6 -> Gm2 = 1/Rs
This was also my first assumption (see post #7), but according to the paper linked in post #8, it's not true for this circuit implementation, (see post #9). Rs is apparently relative small so that it only provides a fine adjustment of total gm.If you increase the current source you increase Gm2 (but it has minor effect since it is source degeneration and Gm2 mostly depends on Rs). for higher gm6 -> Gm2 = 1/Rs.
This was also my first assumption (see post #7), but according to the paper linked in post #8, it's not true for this circuit implementation, (see post #9). Rs is apparently relative small so that it only provides a fine adjustment of total gm.
Why minor effect ? There is no terminology on current source in the equation of Gm2 due to small-signal nature.
This was also my first assumption (see post #7), but according to the paper linked in post #8, it's not true for this circuit implementation, (see post #9). Rs is apparently relative small so that it only provides a fine adjustment of total gm.
Generally you dont choose small value for Rs since you want to have a linear gm
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