Unity-gain bandwidth

The eontribution to the drain current from the gate drain capacitance was found to be small for frequencies within the unity-gain bandwidth and is therefore ignored. The gate current becomes ... 

The drain-source capacitance Qs can be neglected since only a constant drain voltage Vis is applied. The total gate capacitance is given by Cg = tot Q with yf tot ihs total gate area. The unity-gain bandwidth can now be calculated from Eqs. (8), (10) and (12) ... 

The open-loop gain A decreases with increasing frequency, typically by a factor of 10 per decade of frequency and A comes close to 1 (unity gain) in the MHz region. This means the useful bandwidth is at least one or two orders of magnitude lower than at unity gain. This is especially important for pulse experiments or experiments at higher frequencies. 

For a resistive network, Gj(s) is a number which may be greater or less than unity. The feedback in this case produces gain stabilization. Amplifier frequency response is increased (gain-bandwidth relation) and stability is improved. There is also a reduction in electrical noise at the output because of signal cancellation. 

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