The -3 dB point is used to define the bandwidth boundary.

The -3 dB point is used to define the bandwidth boundary.

• A. The frequency at which the output amplitude is reduced by 3 dB
• B. The frequency at which the input equals the output
• C. The phase shift is zero
• D. The gain is unity

Answer: (A)

The bandwidth boundary is defined by where the output has dropped by 3 dB from its passband value. That -3 dB point means the output amplitude is about 0.707 of its maximum, and the power is half of the passband power. This provides a practical, standard cut-off where the signal starts to be noticeably attenuated. So the statement describes the exact criterion used to mark the bandwidth boundary. The other ideas—where input equals output, zero phase shift, or unity gain—don’t define the boundary in terms of how the signal’s strength falls with frequency.

The bandwidth boundary is defined by where the output has dropped by 3 dB from its passband value. That -3 dB point means the output amplitude is about 0.707 of its maximum, and the power is half of the passband power. This provides a practical, standard cut-off where the signal starts to be noticeably attenuated. So the statement describes the exact criterion used to mark the bandwidth boundary. The other ideas—where input equals output, zero phase shift, or unity gain—don’t define the boundary in terms of how the signal’s strength falls with frequency.