Re: Bandwidth of OPAMP
usually the bandwidth of any amplifier can be dependent on gm, R and C
( sometimes L if peaking method is used). gm is a transconductance of an amplifier, R is resistance at the load and C is capacitance seen at the load.
gm is increased when bias current increases, and it helps to achieve a wider bandwdith
in CMOS Opamp, R is usually composed of rds of nmos and pmos. rds is inversely proportional to the current due to the channel length modulation, therefore, increasing bias current reduces rds, which pushes a pole into higher frequency resulting in wider bandwidth.
usually C is fixed even though a bias current is increased if the size of device isnt
changed. but C can be affected if C is miller cap that is related to the gain of a amp cell. usually gain can be expressed as gm*R. generally gm is increased by sqrt of current and R is decreased by 1/current. so gain is decreased by 1/sqrt
of current which leads to decrease in C as well, and it achieves a wider bandwidth
by pushing a pole into higher frequency.
therefore generally, by increasing a bias current, you get wider bandwidth in opamp