Highly Sensitive Broadband SiGe HBT LNA: Genetic Algorithm based Optimization and Design Methodology

This paper extends the work of the authors on highly sensitive broadband silicon germanium heterojunction bipolar transistor (SiGe HBT) low-noise amplifiers with regard to their optimization based on the genetic algorithm and proposes a design methodology. The methodology aims at achieving a sub-1 dB noise figure at room temperature. The amplifier uses inductively degenerated common-emitter transistors in a cascode configuration, and a noise figure close to the minimum achievable one is obtained by biasing the SiGe HBTs at an emitter current density corresponding to minimum noise. Noise matching is achieved by connecting several identical transistors in parallel, while impedance matching relies on limiting the number of passive components for the matching network to the absolute minimum. This is done by the base-collector capacitance used as a network element and by means of an additional noiseless on-chip component. A sub-1 dB noise figure of 0.6 dB is shown by simulation without optimization by the genetic algorithm, with a return loss better than 10 dB, using a 130 nm SiGe HBT process. The bandwidth of the low-noise amplifier spans from 300 MHz to 1.4 GHz. The methodology validates that SiGe HBTs are suitable for broadband ultra-low noise amplifiers for radio astronomy and that the performance of the proposed amplifier can be further optimized.