A GaAs monolithic true logarithmic amplifier for 0.5 to 4 GHz applications

A GaAs monolithic dual-gain amplifier stage for 0.5 to 4 GHz logarithmic amplifier applications was developed and tested. A cascade of six of these stages resulted in a true logarithmic amplifier with a 70-dB dynamic range, operational across this band. A stage gain of 10 dB was chosen for each of two ´arms´ in the dual-gain circuit, but because of -6-dB resistive combiner was used, the gains of both amplifier arms were increased 6 dB. The first arm has 12.7-dB gain and a saturated output power of -8 dBm, and the second arm has 6-dB gain and a saturated output power of +11 dBm. A thin-film network external to the monolithic circuit contains the -6-dB resistive combiner in which the outputs of the two amplifier arms are combined to provide the linear gain of 10 dB at low power levels. The stage gain asymptotically approaches 0 dB as input power is increased. Additional circuit elements printed on the thin-film network are two shorted stubs for gain shaping and one series transmission line to equalize the insertion phase between the two paths.<>