On the Design of Broadband Power-to-Current Low Noise Amplifiers

Aiming for the simultaneous realization of constant gain, accurate input impedance match, and minimum noise figure over a wide frequency range, the circuit topologies and detailed design of two broadband dual-loop negative feedback power-to-current low noise amplifiers (LNAs) are presented in this paper: 1) a resistive indirect-feedback power-to-current LNA, which requires an active part with two output terminal pairs, and 2) a transformer feedback power-to-current LNA, which requires a transformer in its current feedback path having a high turn ratio with high magnetic coupling. For both LNAs the feedback networks and active part implementations are discussed in detail. It is shown that for this purpose a novel stacked transformer can be realized using only two metal layers. The two LNAs are designed to be implemented in a 0.2 m GaAs p-HEMT technology process to verify the theory presented. Counter measures are applied to deal with the effects of bond wires and the effects of transformer parasitics on the circuit performance are analyzed. Simulation results show that the resistive indirect-feedback power-to-current LNA exhibits a 0.6-0.8 dB noise figure, an input return loss well below dB, a 200 mS voltage-to-current gain (which corresponds to 23 dB power gain for a 50 load) from 0.3 GHz to 4 GHz, a dBm third-order input intercept point (IIP3) and a 23 dBm second-order input intercept point (IIP2) at 2 GHz. It consumes 73 mA current from a 4 V power supply. The transformer-feedback power-to-current LNA achieves a 0.5-0.8 dB noise figure, an input return loss of less than dB, a 22 dB power gain from 0.8 GHz to 4 GHz, and a 0 dBm IIP3 and 22 dBm IIP2 at 2 GHz while drawing 53 mA current from the 4 V power supply.