Gain-bandwidth product GBWP, a fixed quantity for any voltage-feedback amplifier (this is not true for current-feedback amplifiers), can be determined from the open-loop gain plot found in a datasheet. Simply pick a point on the linear portion of the open-loop gain response after the –3 dB point, multiply the gain (in V/V, not dB) by the corresponding frequency, and you have the GBWP. You can also use the unity-gain crossover as the GBWP if there are no parasitic poles, but high-speed amplifiers tend to have parasitic poles close to the unity-gain crossover, so we tend to stay away from those when calculating the GBWP. Once the GBWP is calculated, the bandwidth for a given gain or the gain for a given frequency can be determined.
Learn more about GBWP in Great Expectations, as published in the September 2012 issue of Analog Dialogue.
We welcome your feedback. Has this article helped you in your design? Would you like more information on this topic?