may also be used for a transmitter 39 s preamplifier in a wireless terminal unit but in this case it may necessary to place a low capacitive load at its output this is because a typical preamplifier drives the power amplifier whose input impedance may be set to 50 u03c9 a standard impedance in microwave engineering a pull up capacitor cp u2032 400 may be connected in parallel with the pull up inductor lp 410 and turned on and off with its series connected switch 405 as shown in fig4 a for this preferred embodiment according to the invention switch 405 may be implemented with a complementary mosfet cmos u201c transmission gate u201d in which case the resonant frequency may be shifted down and up correspondingly the resonant frequency may be made to fall on another desired frequency band provided that the amplifier functions stably at the shifted band one example of dual band operation may be an amplifier for wireless communication usable for a cellular band around 800 mhz and a pcs band around 1800 mhz time multiplexingly the desired frequency band may be selected by an external signal that controls the cmos switch additional band selectivity may be achieved by employing the circuit shown in fig4 b which is an alternative preferred embodiment to the circuit in fig4 a the preferred embodiment shown in fig4 b can achieve multi band operation with a single driving transistor mn.