1. Field of the Invention
This application relates to an analog switch circuit, and more particularly, to the optimizing circuit characteristics according to the ON/OFF status of the analog switch circuit.
2. Description of the Related Art
Since a metal-oxide-semiconductor field-effect transistor (MOSFET) can easily be downsized and have superior element characteristics as well as readily-integrated process, a MOSFET is usually disposed as an analog switch when a communication system is in need, where the ON/OFF status of the analog switch can be controlled by a bias applied on a gate electrode of the MOSFET. When the analog switch is ON, a carrier channel (N-type or P-type) forms between a drain electrode and a source electrode of the MOSFET, which is equivalent 20 to a resistor present between the drain electrode and the source electrode. When the analog switch is OFF, no carrier channel or only narrow carrier channel exists between the drain electrode and the source electrode of the MOSFET, which is equivalent to a capacitor present between the drain electrode and the source electrode.
In addition to the gate, drain, and source electrodes, the MOSFET may include a body electrode for further tuning. In conventional designs, only one bias is applied on the body electrode, or only one resistor with constant resistance is connected to the body electrode. However, according to the description above, an ON switch and an OFF switch require two completely different element characteristics. Hence, only providing fixed bias to the body electrode or connecting the body electrode to the resistor with fixed resistance cannot further optimize the analog switch, and better quality for signal transmission cannot be obtained.