Explain the gain-bandwidth product concept and how it governs the closed-loop bandwidth for a given op-amp.

Explain the gain-bandwidth product concept and how it governs the closed-loop bandwidth for a given op-amp.

• A. GBW varies with frequency and gain.
• B. GBW is the product of closed-loop gain and bandwidth and is not constant.
• C. GBW is roughly constant; A_cl × f_cl ≈ GBW; as closed-loop gain increases, bandwidth decreases proportionally.
• D. GBW equals the ratio of output voltage to input voltage.

Answer: (C)

The gain-bandwidth product describes how an op-amp trades gain for speed. Because the internal compensation creates a dominant pole, the open-loop gain falls as frequency increases, so you can’t have both high gain and wide bandwidth at the same time. The practical rule is that the closed-loop gain times the closed-loop bandwidth stays roughly constant, equal to the op-amp’s GBW (the unity-gain frequency). So, for a given op-amp, the closed-loop bandwidth is about GBW divided by the closed-loop gain: f_cl ≈ GBW / A_cl. As you raise the desired closed-loop gain, the bandwidth drops in inverse proportion. This explains why higher closed-loop gains give narrower bandwidths, while lower gains allow wider bandwidths, within the range where the op-amp behaves like a single-pole system. In real devices, there are small variations at very high frequencies or gains due to additional poles, but the described relationship is the standard, useful approximation.

The gain-bandwidth product describes how an op-amp trades gain for speed. Because the internal compensation creates a dominant pole, the open-loop gain falls as frequency increases, so you can’t have both high gain and wide bandwidth at the same time. The practical rule is that the closed-loop gain times the closed-loop bandwidth stays roughly constant, equal to the op-amp’s GBW (the unity-gain frequency). So, for a given op-amp, the closed-loop bandwidth is about GBW divided by the closed-loop gain: f_cl ≈ GBW / A_cl. As you raise the desired closed-loop gain, the bandwidth drops in inverse proportion. This explains why higher closed-loop gains give narrower bandwidths, while lower gains allow wider bandwidths, within the range where the op-amp behaves like a single-pole system. In real devices, there are small variations at very high frequencies or gains due to additional poles, but the described relationship is the standard, useful approximation.