FET switch 原理

GaAs FETs as control devicesGaAs FETs as Control Devices
APN2015
Gallium arsenide MESFETs are being used in RF control device applications as switches and attenuators. They are very easily adapted to monolithic circuit form, dissipate essentially no power and can easily be designed into broadband circuits. The RF signal flows from source to drain, while the RF isolated gate is the voltage control. The high impedance “off state” is attained by applying a DC voltage on the gate more negative than the “pinch-off” voltage (VP). In this condition the source-drain channel is “pinched off.” The capacitance is typically 0.25 pF per mm of gate periphery (see Figure 1A). The “on” state occurs when zero DC bias is applied to the gate (see Figure 1B). The channel from source to drain is “open” and represents a 2.5