In a typical inverting op-amp configuration, increasing the feedback resistor value tends to

In a typical inverting op-amp configuration, increasing the feedback resistor value tends to

• A. No change
• B. Decrease bandwidth
• C. Increase bandwidth
• D. Undefined

Answer: (B)

Gain-bandwidth tradeoff in an op-amp governs how bandwidth changes when you change closed-loop gain. In an inverting configuration, the closed-loop gain magnitude is set by the ratio Rf/Rin. If you increase the feedback resistor while Rin stays fixed, that ratio grows, so the closed-loop gain becomes larger in magnitude. Real op-amps have a finite gain-bandwidth product, so the product of the closed-loop gain and the closed-loop bandwidth remains approximately constant. Therefore boosting Rf lowers the bandwidth to keep that product roughly the same. For example, with a gain-bandwidth product of about 1 MHz, moving from a gain of -1 to -10 reduces the bandwidth from ~1 MHz to ~100 kHz. So the bandwidth decreases.

Gain-bandwidth tradeoff in an op-amp governs how bandwidth changes when you change closed-loop gain. In an inverting configuration, the closed-loop gain magnitude is set by the ratio Rf/Rin. If you increase the feedback resistor while Rin stays fixed, that ratio grows, so the closed-loop gain becomes larger in magnitude. Real op-amps have a finite gain-bandwidth product, so the product of the closed-loop gain and the closed-loop bandwidth remains approximately constant. Therefore boosting Rf lowers the bandwidth to keep that product roughly the same. For example, with a gain-bandwidth product of about 1 MHz, moving from a gain of -1 to -10 reduces the bandwidth from ~1 MHz to ~100 kHz. So the bandwidth decreases.