Integrated low noise amplifier with capacitive shunt feedback impedance matching for radio astronomy

The noise performance of integrated low noise amplifiers (LNAs) is impaired by on-chip inductors owing to their low-quality factor, especially when inductors are used in the signal path at the input, such as for the inductively degenerated common-emitter amplifier. The inductively degenerated common-emitter configuration is largely used in LNA design, owing mainly to its ability to achieve impedance and noise matching simultaneously. This paper proposes an LNA configuration that achieves impedance matching and noise matching simultaneously without an inductor in the input signal path, owing to capacitive feedback and transistor sizing. Only the resistive component of the optimum noise resistance is matched to the source resistance. The impact of the mismatch due to the reactive component to the noise figure is reduced by the ratio G_s/R_n. A technique initially developed for the broadband matching of a single-layer microstrip patch antenna is used for the output matching network. Using a 130 nm silicon–germanium heterojunction bipolar transistor process, simulation results indicate a noise figure of 2.3 dB, a gain of 26 dB and S₁₁ and S₂₂ that are better than −12dB at 1.42 GHz. This frequency corresponds to the 21 cm hydrogen line. This novel multi-stage LNA can be used for the detection of electromagnetic radiation from neutral hydrogen atoms from space in radio astronomy and the proposed design methodology can be generalized to LNAs.