Unilateralization of MMIC Distributed Amplifiers

Abstract

This paper presents an unilateralization technique for distributed amplifiers (DAs) based on the transformer coupling between the gate and drain lines. Theoretical analysis of the DA indicates that the voltage waves in the gate and drain lines can be described by a system of linear partial differential equations. The transformer coupling between the lines allows for cancellation of the reverse transmission coefficient of the system. There is an optimal value for the coupling coefficient between the lines that unilateralizes the DA. This optimal coupling coefficient is derived in terms of the gate-drain capacitance and capacitances of the gate and drain lines. Using the proposed technique, two monolithic microwave integrated circuit DAs are designed and implemented in a 0.1- μm GaAs pHEMT process. The first DA provides average gain of 10 dB and 3-dB bandwidth (BW) of 39 GHz. The amplifier exhibits the minimum noise figure (NF) of 2.3 dB and the maximum output 1-dB compression point ( P1 dB) of 14.0 dBm, while consuming 80 mW from a 2-V supply. The second amplifier, composed of two cascaded coupled-line DAs, provides average gain of 19.2 dB, 3-dB BW of 37.5 GHz, the minimum NF of 2.3 dB, and the maximum P1 dB of 12.6 dBm. It consumes 131 mW from a 2-V supply. The designed amplifiers can operate with supply voltages as low as 0.5 V to reduce power consumption, while their gain, BW, and NF are preserved. The maximum ratio of gain-bandwidth product to power consumption GBW/Pdc of 11.9 GHz/mW is provided by the cascaded DA.