The bootstrapped gate FET (BGFET)-a new control transistor

Si PIN diodes are used almost exclusively when low cost, low distortion variable attenuators are needed. PIN diodes can obtain an input third order intercept IIP3 of +20 to +40 dBm, but at the expense of complicated biasing and high current consumption. GaAs MESFETs used as attenuators require only a control voltage and are easily integrated into monolithic circuits. A major disadvantage of the GaAs MESFET is its high level of distortion. In a series attenuator configuration, a typical GaAs MESFET IIP3 is 0 dBm at 10 dB attenuation. Therefore, GaAs MESFETs are used only under very low level input signals. This precludes their use from most high volume applications such as cable television, DBS receivers and cellular telephones. We present a new transistor, a bootstrapped gate FET (BGFET) which provides about an approximate 20 dB improvement in distortion over a standard GaAs MESFET.