Direct-digital frequency synthesizers (DDSs) are highly attractive in wireless communications because of their fast frequency hopping characteristics. Generally, DDSs adopt truncation and thermometer decoding for high-frequency resolution and monotonicity, respectively. However, the truncation causes poor spectral purity due to periodical errors in phase accumulation. Also, the thermometer decoding scheme of digital-to-analog converter (DAC) requires many current sources, which creates large parasitic components and nonlinearity. This article presents several techniques for addressing the above challenges. First, a fixed-weight decoder (FWD) with an auxiliary DAC is proposed to remove the truncation spur in the phase accumulation. Since FWD controls the amplitude regardless of the phase, it removes the periodic errors without significant power increment. Second, the proposed tristate decoding scheme reduces the number of current sources to reduce timing mismatches and capacitances. Finally, a fine current source reusing technique is developed to reduce the number of current sources and power consumption. The proposed DDS was fabricated in a 65-nm CMOS technology. The worst spurious-free dynamic range (SFDR) is 57.35 dBc at 2.5 GHz with a power consumption of 104 mW. The measured figure of merit is 18 124 GHz <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot$</tex-math> </inline-formula> 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${}^{(SFDR/6)}$</tex-math> </inline-formula> /W.

This paper proposes a novel packaging and large-scale antenna-assembled structure for a printed circuit board (PCB) that reinforces productivity, facilitates cost reduction, and maintains reliability. This was achieved by splitting the antenna from the main board and packaging it into a radio-frequency integrated circuit. In addition, two innovative solutions—an externally attachable flexible PCB antenna and a PCB-embedded coaxial line—are introduced to overcome the degradation in antenna performance and vertical RF transition loss in the proposed low-cost hybrid PCB. First, the proposed externally attachable flexible PCB antenna and a parasitic aircoupled antenna, which were easily assembled on the PCB, achieved an antenna efficiency of 95% and an impedance bandwidth of 7 GHz. Second, the fabricated coaxial line exhibited enhanced impedance matching over a wide frequency range of 30–40 GHz and improved insertion loss of approximately 1.4 dB. Furthermore, the packaged antenna, composed of 256 dual-polarized antenna elements per stream, incorporated a 39 GHz CMOS-based 16-channel phased-array transceiver IC. The set-level beam-forming measurements were verified considering an effective isotropic radiated power of 55 dBm at boresight and a steering range &gt;±60°. In addition to being suitable for mass production in terms of cost and reliability, the proposed structures and solutions met the required antenna and beam-forming performance for commercial 39 GHz base stations without sacrificing performance.