Abstract
This brief proposes a variable gain power amplifier (VG-PA) with stable linearity for n257/n258 frequency band applications. A switched-capacitor array is proposed in the cascode (CC) circuit to control the gain while maintaining linearity. A compensation inductor is introduced between the common-emitter (CE) and common-base (CB) transistors to suppress the phase variation. For the proof of concept, the VG-PA was fabricated in a 0.13- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> SiGe BiCMOS technology with a core size of 0.59 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 0.46 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Measurements show that at 24/26/28/29.5 GHz, over 5.7/5.5/7.0/7.5-dB gain tuning range, the output 1-dB compression point (OP1dB) is better than 14 dBm with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ {\Delta }$ </tex-math></inline-formula> OP1dB less than 1.2 dB, the third-order output intercept point (OIP3) is better than 22 dBm with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ {\Delta }$ </tex-math></inline-formula> OIP3 less than 3.4 dB, and the phase variation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ {\Delta }{\varphi }$ </tex-math></inline-formula> ) is from 3 to 9.5°. To the author’s best knowledge, this work has the lowest linearity variation among Si-based variable gain amplifiers at millimeter-wave frequency band.
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