Design of a 60-GHz High-Output Power Stacked- FET Power Amplifier Using Transformer-Based Voltage-Type Power Combining in 65-nm CMOS

In this paper, a 60-GHz transformer (TF)-based voltage-type-combined single-stage stacked field-effect transistor (FET) power amplifier (PA) is demonstrated using a 65-nm CMOS process. A stacked-FET structure is adopted in the PA design to overcome the low breakdown voltage limit of MOSFETs. The TF-based voltage-type combiner used in the design has 0.9-dB insertion loss with a compact size of 0.023 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The additional output balun is utilized to transform the differential output of the voltage-type combiner to the single-ended output for testing consideration. The thermal problem of the PA was discovered and improved during measurement. With a 3-V supply, the measured PA achieves the saturated output power ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm {SAT}}$ </tex-math></inline-formula> ) of 21.8 dBm, the maximum power-added efficiency (PAE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) of 12.4%, and a 8.7-dB small-signal gain <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(\vert S_{21}\boldsymbol \vert)$ </tex-math></inline-formula> at 60 GHz with the loss of the output balun. Without considering the loss of the output balun, which is 0.825 dB, the measured PA achieves <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathrm {SAT}}$ </tex-math></inline-formula> of 22.8 dBm, the PAE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 15.9%, and a 9.5-dB gain at 60 GHz.