130 GHz Band CMOS Amplifier with Miniaturized Interstage Circuit by Stacked Radial Stubs

Low loss matching circuit is a key issue in 130 GHz band multi-stage CMOS amplifier design. We reported the use of radial stubs as AC GNDs is effective to achieve low loss matching circuit. In this paper, we propose stacked radial stub for interstage matching circuits. This stacked radial stub consists of two radial stubs stacked vertically using multi-layered metals. It works as two independent radial stubs whereas it consumes one radial stub’s die area, therefore compact and low loss interstage matching circuit can be realized. The proposed stub has been designed to obtain isolation between stacked radial stubs over 40 dB in 130 GHz band and adopted into the interstage matching circuits of three-stage amplifier. This amplifier has been fabricated in 45nm SOI CMOS process and it shows peak gain of 9.9 dB at 135.8 GHz by measurement.