Design and analysis of a high-performance cascode bipolar low noise amplifier with shunt feedback capacitor

In this paper, a cascode bipolar low noise amplifier (LNA) employing a shunt feedback capacitor is presented, for which the linearity and the noise figure (NF) can be optimized by reducing the transistor size and degeneration inductance. We also show that the second-order interaction, which affects the third-order nonlinearity, becomes insensitive to low-frequency input termination as the DC current increases. Finally, the method of removing the low-frequency trap is presented. The fabricated LNA in 0.35-mum SiGe BiCMOS process showed NF of 0.9 dB with 16-dB power gain and IIP₃ of +11 dBm with current consumption of 10 mA from 2.8-V power supply at 900 MHz. The demonstrated LNA satisfies stringent sensitivity and linearity requirement of code-division multiple-access (CDMA) applications quite well.