STATIC ELECTRICITY PROTECTION CIRCUIT

摘要

PURPOSE:To prevent a damage to a transmission high frequency amplifier circuit even when a high voltage of static electricity is applied carelessly to an antenna. CONSTITUTION:A microstrip line 18 is connected between a GND and an output transmission line of a transmission high frequency amplifier circuit 10 and a variable capacitor 20 is connected in parallel with the microstrip line 18. The microstrip line 18 is connected to ground and the length is selected to be 1/4 wavelength of a signal with a center frequency at an operating high frequency band. The parallel connection circuit comprising the microstrip line 18 and the variable capacitor 20 has an impedance almost infinite with respect to a high frequency signal and gives no effect on the high frequency amplifier circuit 10 and has nearly a zero impedance with respect to DC, then even when a transmission reception antenna is in contact with cloth of a person or the like and a high voltage of static electricity is applied to the antenna, the charge is discharged to the ground GND through a no loss distributed constant line.