High speed opamp -depends on GBW or BW?

[analogartist]

Wondering what causes High speed in an opamp(closed loop).. I derived the step input for an closed loop single pole system to be
V0(1-e(-wf))
where wf is the closed loop bandwidth= wo(1+βAo)

where wo is open loop BW , Ao is open loop gain and β is feedback factor..

Is it good to approximate this wf to wo*β*Ao... considering wo << wo*β*Ao.

If I do this then the speed of the system depends on GBW and not BW.? But most of the books say speed depends on the BW(Rise time =0.35/BW).

Put it in another way
If I have an opamp1 which has say a BW of 300MHz and GBW of 1MHz and
and another opamp2 which has a BW of 500Mhz and GBW of 800Hz. Which is is faster pamp1 or opamp2?

Would appreciate enlightment on a simple (bothersome ) question?

Thanks

 

[imjasmine]

http://www.elektrotekno.com/forum-10.html

visit this link to download the required stuff

cheers

Wondering what causes High speed in an opamp(closed loop).. I derived the step input for an closed loop single pole system to be
V0(1-e(-wf))
where wf is the closed loop bandwidth= wo(1+βAo)

where wo is open loop BW , Ao is open loop gain and β is feedback factor..

Is it good to approximate this wf to wo*β*Ao... considering wo << wo*β*Ao.

If I do this then the speed of the system depends on GBW and not BW.? But most of the books say speed depends on the BW(Rise time =0.35/BW).

Put it in another way
If I have an opamp1 which has say a BW of 300MHz and GBW of 1MHz and
and another opamp2 which has a BW of 500Mhz and GBW of 800Hz. Which is is faster pamp1 or opamp2?

Would appreciate enlightment on a simple (bothersome ) question?

Thanks

 

[analogartist]

What is this link... goes to some foreign language website...?

 

[fxxjssc]

hi analogartist,
i'am not sure GBW is Gain-bandwidth product or not. for one pole system,if GBW stands for gain-bandwidth, as soon as you gets GBW, BW can be derived from GBW. For example, GBW=10M, (80db at 1K), BW=10M(0db at 10Mhz)
may help.