Multifunctional Single-Ended and Balanced Low-Noise Amplifiers With Co-Designed Bandpass Filtering Capabilities

The comprehensive RF co-design techniques for single- and multistage single-ended and balanced bandpass filtering low-noise amplifiers (BPF-LNAs) are presented. They are based on complex-matched bandpass filtering matching networks (BPF-MNs) and bandpass filtering balun matching networks (BPF-BMNs) with quasi-elliptic transfer functions that directly match the transistor impedances while at the same time exhibiting bandpass filtering (BPF) characteristics. Frequency dependent interresonator coupling elements are used in the BPF-MN to enhance the transfer function selectivity by means of transmission zeros (TZs). A technique to intrinsically switch-off the BPF-LNAs is also reported. The concepts have been validated at C- and S-bands through the design, manufacturing, and testing of four prototypes, namely: Prototype 1: a single-stage BPF LNA with f_cen of 4.63 GHz, gain of 12.28 dB, noise figure (NF) of 2.52 dB, and one TZ at the lower side of the passband, Prototype 2: a single-stage BPF-LNA with f_cen of 4.72 GHz, gain of 13.76 dB, NF of 2.26 dB, and two symmetrically allocated TZs, Prototype 3: a multistage BPF-LNA with f_cen of 4.65 GHz, gain of 20.57 dB, NF of 2.54 dB, and three TZs asymmetrically allocated on either side of the passband, and Prototype 4: a balanced BPF-LNA with f_cen of 3 GHz, gain of 16.8 dB, and NF of 1.41 dB. By removing the dc biasing, the single-stage, multistage, and balanced BPF-LNAs can be intrinsically switched-off with an isolation (IS) >25 dB across an ultrabroad frequency range.