An analog switch uses a control signal to connect or disconnect an analog signal path. The control chooses the conducting state; the transmitted electric potential difference is not restricted to a binary logic value. Real devices have finite analog switch on-resistance, leakage and parasitic capacitance. The primary tutorial describes a bilateral CMOS switch formed from complementary transistors.[ref]
For an original loading example, connect an ideal source through a stipulated on-resistance to a load. The output isThe closed switch therefore changes the amplitude even before any switching transient is considered. This is a chosen resistor model, not a specification for a particular part. Variation of on-resistance with signal level can additionally produce distortion.
An open switch is also not an ideal infinite impedance. For example, a stipulated analog switch leakage current into changes the node potential at , or in a millisecond if that model remains valid. A high-impedance measurement can be sensitive to this small current.
On a bench, compare the transmitted level and the open-state drift with the same source, load and oscilloscope conditions. Analog switch charge injection concerns the control transition itself, while settling time concerns how long the complete circuit needs to approach its final value. Those effects are separate from the static conducting-state error.
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