OPA211 datasheet report a bandwidth of 45Mhz when gain is 1 and a bandwidth of 80Mhz when gain is 100. How is possibile? Is a documentation error?
The expected bandwidth is 450Khz...
Thnak you.
Fausto,
No, there is no error in the OPA211 PDS but rather what you describe is a difference between the Unity-Gain Bandwidth and Gain-Bandwidth-Product as shown below.
If you look at the graph of open-loop Gain and Phase vs Frequency below, you will see that the gain plot crosses the 0dB axis (close-loop Gain=1) at 45MHz so the unity-gain bandwidth is 1 x 45MHz=45MHz. However, when you look at the frequency at which the gain plot (below) intersects 40dB axis (close-loop gain=100), it occurs at 800kHz and NOT at 450kHz so the Gain-Bandwith Product is: 100 x 800kHz = 80MHz.
The Unity-Gain bandwidth and Gain-Bandwidth-Product are the same ONLY when the Gain/Phase response is a single-pole system (at least until the open-loop gain crosses the 0dB line). However, when a second-pole effects the gain response above 0dB, as it may be seen occurring around 6MHz in the case of OPA211, the unity-gain and a gain-bandwidth-product are NOT the same.
Regards,
Marek LisSr Application EngineerPrecision Analog - Burr-Brown ProductsTexas Instruments - Tucson