Weak inversion biasing - need for or advantage of

[mickey_melomane]

weak inversion

What is the (need for/advantage of) biasing a transistor in Weak inversion region? Plz list some tutorials if anyone might know!

Sidharth

 

[safwatonline]

weak inversion current source

largest gm/ID for MOS

 

[saro_k_82]

gm in weak inversion

plus you also get better bias margins

 

[mickey_melomane]

Re: Weak inversion biasing

Could you please explain in detail as to why you need larger gm/I ratio... and what is meant by bias margin... Shouldn't Vgs increase for higher drain currents, provided Vd does not fall below Vdsat...?

 

[saro_k_82]

Re: Weak inversion biasing

Biasing in weak inversion means making the device much larger so that the VGSeff is not much to drive the required current. So VDS sat becomes low which provides more voltage range where the devices work properly.
More gm provides more gain. gm can also be improved by increasing I., which makes gm/I the figure of merit.

 

[mickey_melomane]

Weak inversion biasing

Does the same thing apply to the input transistors of a 5-T NMOS input differential amplifier?

Or which amplifiers of a 5-T diff pair, be biased in weak inversion. (assuming current source load or current mirror load)