On-resistance (RON) is the resistance of the mux path between the drain and source terminal. It is the resistance introduced by the mux to the circuit when the mux is in the closed position. There are many factors that affect RON, such as:

• Temperature
• Input voltage
• Supply voltage
• Gate length “W”

Another important specification related to RON is RON flatness. RON flatness is a measure of how the RON changes over the operating voltage range of the mux. RON flatness can vary dramatically, depending on the type and design characteristics of the mux.Especially the audio applications require low flatness values, because the flatness causes harmonic distortion that should be kept as low as possible

Ideally, RON is as low as possible in order to keep the signal losses and propagation delays small. To achieve very low resistance and flatness for analog mux, two parameters are important. For both PMOS and NMOS, the size must be large as possible, and the voltage thresholds must be low as possible. Increasing the width and length (W/L) ratio of the silicon of a MOSFET not only increases the cost of the mux, but also results in higher parasitic capacitance and a larger silicon area. This larger parasitic capacitance reduces the bandwidth of the analog mux that can pass through the mux without distortion.