Design Aspects of Single-Ended and Differential SiGe Low-Noise Amplifiers Operating Above f<sub>max</sub>/2in Sub-THz/THz Frequencies
Sumit Pratap Singh, Timo Rahkonen, Marko E. Leinonen, Aarno Pärssinen
Abstract
This article presents a single-stage single-ended (SE) and a multistage pseudo-differential cascode low-noise amplifiers (D-LNA) with their center frequencies at 235 and 290 GHz, respectively. Both low-noise amplifiers (LNAs) are designed beyond half of the maximum frequency of oscillation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_\text{max}$</tex-math> </inline-formula> ) in 130-nm SiGe BiCMOS technology with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{t}/f_\text{max}$</tex-math> </inline-formula> of 300 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$/$</tex-math> </inline-formula> 450 GHz. Implications of gain-boosting and noise reduction techniques in cascode structure are analyzed and it is observed that beyond <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f_\text{max}}/2$</tex-math> </inline-formula> , these techniques do not provide desired benefits. The single-stage SE LNA is designed to ascertain the theoretical analysis, and the same analysis is further implemented in staggered tuned four-stage LNA. Single-stage SE LNA provides a small signal gain of 7.8 dB at 235 GHz with 50 GHz of 3-dB bandwidth by consuming 18 mW of power. Four-stage differential LNA gives 12.9 dB of gain at center frequency 290 GHz and 11.2 dB at 300 GHz by drawing 68 mA current from the 2-V supply. The 3-dB bandwidth of differential LNA is measured to be 23 GHz. Noise figure measurements of both LNAs are performed using a gain-method technique with their measured noise figure values of 11 and 16 dB, respectively. This work successfully demonstrates the possibility of using a Si-based process to implement amplifiers beyond <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_\text{max}/2$</tex-math> </inline-formula> . To the authors’ best knowledge, the four-stage differential LNA achieves, without any gain-boosting technique, the highest gain at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2/3(f_\text{max})$</tex-math> </inline-formula> with decent noise figure performance in SiGe technology.