Hi

I have a question, how can we calculate the closed loop amplifier bandwidth?
I mean by the closed loop, the inverting amplifier.

Thank You

 

Hello,

Have a look at the following PDF:
sloa011Understanding Operational Amplifier Specifications.pdf

Bertus

 

Jim Karki's paper is good but rather laborious for a simple task. Normally the closed loop bandwidth is defined as the point at which the gain is down 3dB from "0" frequency gain. Look at the op amp's open loop gain curve on its data sheet (if there is no open loop gain curve you got the wrong op amp) enter the y axis at the closed loop gain and cross over till the curves intersect. At the intersection drop down to the frequency axis and read the 3dB freq i.e. the closed loop BW.

 

There is a specification called GBW - Gain Bandwidth product. For the open loop case it is the product of open loop gain gain and the open loop bandwidth. If you change the gain to the closed loop value, the closed loop bandwidth will increase so that the product of closed loop gain and closed loop bandwidth is equal to the same constant GBW.

 

Jim Karki's paper is good but rather laborious for a simple task. Normally the closed loop bandwidth is defined as the point at which the gain is down 3dB from "0" frequency gain. Look at the op amp's open loop gain curve on its data sheet (if there is no open loop gain curve you got the wrong op amp) enter the y axis at the closed loop gain and cross over till the curves intersect. At the intersection drop down to the frequency axis and read the 3dB freq i.e. the closed loop BW.

You need to keep in mind that an inverting unity gain amp (closed loop gain=-1) has half the bandwidth of a noninverting unity gain amplifier (closed loop gain=+1), due to the fact that the inverting amp has a feedback ratio of Rs/(Rs+Rf), which is 0.5 in this case.