Can anyone explain passive and active biasing?

:lol:

I would guess (by the names)

That passive uses something like voltage divider networks to fix bias.

Active probably has something like a feedback circuit to control gain.

Maybe more knowlegable ppl can "enlighten" us. But, I will look up and try to find answer.

WA

right

The above discussion is close. Passive bias uses the device's own characteristics. One example would be putting a source rssitor in a depletion mode fet. The old traditional method of bjt bias uses a bypassed emitter resistor and base voltage derived from the power supply or collector voltage.

Active bias meaures the drain current and uses an external transistor or op amp to adjust the transistor gate/base voltage.

Re: right

flatulent said:

The old traditional method of bjt bias uses a bypassed emitter resistor and base voltage derived from the power supply or collector voltage.

Active bias meaures the drain current and uses an external transistor or op amp to adjust the transistor gate/base voltage.

Click to expand...

Is there any books talk about bjt biasing topics? :roll:

the active biasing has the ability to make the working point more ability but it need more space .
i have find some about it in a place ,but now i'v forget where
but you can search with google i think you can find some about it

Active biasing is often used in rf power amplifiers where emitter or source is grounded. Such amplifiers are usually dissipating heat. To improve temperature stability negative dc feedback is used to keep average collector (drain) current constant. Feedback is usually made with PNP transistor.

Hi,
Passive biasing is still used widely in biasing of discrete circuits and transistors, it depends on the voltage division using resistors potential divider, its main advantage is the simplicity of biasing, yet the main disad is the high sensitvity to supply variation, as it directly depends on the supply for obtainig the desired voltage drop.
Active biasing is dominant in IC design, tolerances in monolithic resistors up to 20% make it un-practical for passive basing on-chip.
Active biasing is composed of a bias cell core(PTAT,constant-gm,band gap) which generates a reference current, and current mirroring transistors to mirror current from bias cell to the the desired circuit with a well defined ratio from the refernce current.
Active biasing topics can be found in many literature, Design of Analog Integrated circuits, by P. Gary and Meyer is a good place to read about it.
regards,