Switch Tansistor Topology
An analog or bilateral switch consists of an n-channel transistor in parallel with a p-channel transistor. Given this configuration, as the input voltage or VI approaches V+, the n-channel conductance decreases and the p-channel increases. This results in a RON that is much flatter than any one transistor type switch (as shown in the figure). A flat RON is especially important if the signals that the switch is passing is rail to rail, such as an audio signal.
Using this type of architecture, the overall RON is very low and flat without the expense of increased power consumption. However, this architecture does increase the overall capacitance of the switch. As a result the bandwidth of the analog switch will be lower, but this tradeoff is acceptable given the nature of the application.
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