9.11 : 周波数応答

Consider a guitar pickup connected to a buffer amplifier. This buffer amplifier, with a non-inverting op-amp, bridges the guitar's high impedance and the amplifier's low impedance.

The Bode magnitude plot of the op-amp maintains a constant gain below the corner frequency and it decreases at a rate of negative twenty decibels per decade beyond it.

The circuit is transformed into an equivalent frequency-dependent configuration, with the output voltage linked to the frequency-dependent gain and the input voltage.

Writing the nodal equation and substituting the expression for the op amp's input voltage yield the circuit's transfer function, which depends on the gain of the ideal non-inverting amplifier.

Using the expression for the amplifier gain, the transfer function can be expressed in terms of the DC gain of the non-inverting amplifier.

Approximations lead to a simplified transfer function, expressed using the corner frequency and ideal gain.

The gain bandwidth product equals the DC gain multiplied by the corner frequency.

This shows that for higher gains, bandwidth decreases, keeping the gain-bandwidth product constant and limiting the effective frequency range.