Newbie level 4
I am checking the definition of Gain Bandwidth Product in op amp design, but the definitions are different on different materials. Is there anybody can show me the correct definition? Thank you very much!
LvW said:The gain-bandwidth-product (GBW) is the product GBW=Ao*fg .
(Ao=opamp open loop dc gain, fg=3-dB-frequency of the magnitude function).
In most cases the opamp is universal compensated and can be seen as a single pole model. In these cases, the GBW is approximately equal to the transit frequency fT where the gain has dropped to 0 dB.
LvW said:Yes, that´s right. But only in case of universal compensation !
The answer is easy: In a single pole response the gain drops with 20 dB/dec. - which means: When the frequency increases by a factor of 10, then the magnitude gets smaller by a factor of 10. Thus, the corresponding product remains constant.
Comment: fc in your formula is the 3-dB-point of the closed loop gain !
In the Perspective of a hardware circuit (with ampr APEX PA107DP)..how to find the GBP? should the feedbck resistance be removed? if so wen finding unity gain bandwith in open loop (open loop gain=1) the freq will be somewer in 100's of MHZ but the signal generatr is only upto 15MHZ??
Plz help me with my query...thank u!!
Thank u fr ur reply...but the roll off freq in my case is not 20db/decade exactly..and with the closed loop the unity gain is met at freq of 120KHz. Do I need to compensate my circuit and how?
This is a measured value and i'm using a very little gain of 10 or 20 dB (which is Rf=15K,30K and Rin=1.5K)...will my circuit be stable if I increase the Rf eventuallly the gain ??
No i din't try simulating yet,but there is a sight of oscillations near the same freq