Why could increasing biasing currents increase the bandwidth?

[Evy]

How can an increase of biasing currents increase the bandwidth of a negative feedback amplifier? Please explain in easy terms since I am pretty new to electronics. Thanks.   

[w2aew]

In general - increased bias currents mean that lower resistances are generally used.  For example, a load resistor might be 200 ohms instead of 20kohms.  Why does this affect BW?  In a word - parasitics.  Every component has some (unwanted) parasitics like lead inductance, shunt capacitance.  These parasitics are generally related to the physical construction of the device, not the value.  So, a 200 ohm resistor will have the same parasitic inductance and capacitance as a 20kohm resistor.  At a given frequency, the parasitic elements will alter the value of a 20k resistor much more than a 200 ohm resistor - thus making the 200 ohm resistor usable at higher frequencies.

[rfeecs]

In general - increased bias currents mean that lower resistances are generally used.  For example, a load resistor might be 200 ohms instead of 20kohms.  Why does this affect BW?  In a word - parasitics.

It could help with parasitic capacitances, but not inductances.  Higher current could charge/discharge capacitances faster.  As you say, for smaller resistances, capacitance will have a smaller effect but inductance will have a larger effect.

For bipolars, higher current would give higher transconductance, which might help with gain BW product

The question is too vague.

[danadak]

Confirming its a direct impact on Ft.


https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-720j-integrated-microelectronic-devices-spring-2007/lecture-notes/lecture37.pdf


Regards, Dana.