Direct Digital RF Technology - Challenges for Beyond Nyquist Frequency Range

Since the maximum operational frequency of digital RF based on A/D and D/A is Nyquist frequency, it has been difficult to apply digital RF concept to higher microwave frequency range. In this paper, direct digital RF technology is introduced to break this Nyquist limit. This technology utilizes the higher-order Nyquist Zones (beyond the Nyquist frequency range) and higher microwave frequency signal can be handled directly. Higher order direct RF undersampling architecture is introduced for receiver and a fabricated results of 28GHz-band receiver using 1GHz sampling clock will be shown. A 1-bit bandpass $\mathbf{\Delta}\mathbf{\Sigma}$ modulator is introduced for transmitter which generates a 26GHz-band RF signal directly from 8Gbps 1-bit digital stream. In order to enhance the image signal level and SNR, RZ signaling and Manchester coding techniques are examined. This direct digital RF technology brings really digital rich microwave/MMW transceivers in future CMOS era.