Electronic – Op-amp gain bandwidth product

operational-amplifier

I've had this question for a while.

Assume you have an otherwise perfect op-amp with a gain-bandwidth product of 5 MHz. You input a signal of 50mVp-p and amplify it by 10x. This limits your bandwidth to 500 kHz. Now, say you stack another op-amp on the output and configure that as a 10x amplifier. Your overall bandwidth is 500 kHz but you have amplified by 100x, so your GBWP is 50 MHz. Where is the flaw in this logic?

Best Answer

Your logic is sound. More opamps means more gain for a given bandwidth.

Compensated op-amps are made with a single dominant pole so the gain/bandwidth product is constant. If this isn't working for your application, use a decompensated amp and do the compensation network yourself.