Dear Support,
the OPA1611 datasheet says that GBW is 80 MHz @ Gain =100 and is equal to 40 MHz @ Gain = 1.
Could you please explain me such a strange behavior ? Is data in the datasheet correct ?
Does GBW = 80 MHz @ Gain =100 really means I can set the gain @ 100 with an available bandwidth of 80MHz ?
That sounds really strange to me...
Thank you for your time.
Best,
Alberto
Alberto,
If the AOL plot vs frequency had only a single (dominant) pole, the unity-gain bandwidth and GBW would be the same and equation BW=GBW/Gain would work for ALL gains. However, some op amps (including OPA1611) have a second pole (fp2~10MHz - see below) before zero (dB) crossing, which causes the above equation not to work for low gains. In the case of OPA1611, for gains higher than ~10 (or >20dB and thus frequency below 2nd pole) the equation works well and therefore for Gain of 400, BW = 80MHz/400=200kHz - this may be confirmed graphically by looking at the plot below.
