# Why feedback resistance is high?

simulate this circuit – Schematic created using CircuitLab

In this drain to gain feedback resistance biasing circuit, it is said that the feedback resistance Rg is large and usually in $M\Omega$ range. But no current flow through this resistance.

So why it is needed to be large?

Any value of this resistance should serve the purpose as there is no current or power absorption.

• Sometimes an input is on the gate and this might prefer to see higher impedance components. – Andy aka May 6 '14 at 15:02

• The input impedance is the parallel combination of the resistor and the input capacitance of the MOSFET- which is gate-source capacitance plus gate-drain capacitance $\cdot$ (|gain| + 1). – Spehro Pefhany May 6 '14 at 15:35