A Highly Power Efficient 2×3 PIN-Diode-Based Intercoupled THz Radiating Array at 425GHz with 18.1dBm EIRP in 90nm SiGe BiCMOS

Efficient THz generation in silicon technologies has been of great interest over the recent years, as it enables an integrated low-cost solution for sensing, radar, communication, and spectroscopy [1]. Due to the limited
$\mathrm{f}_{\mathrm{T}}/\mathrm{f}_{\max}$
of transistors, direct THz generation using a fundamental oscillator is not feasible; therefore, various approaches have been developed based on harmonic extraction and the frequency multiplication of a fundamental oscillator [2]. In these techniques, the nonlinearity of transistors is utilized to generate higher harmonics from a fundamental oscillator or frequency-multiplier cells; however, such systems have a poor efficiency and low radiated power due to device limitations. To compensate for the low generated power, a coherent array scheme is preferred to increase EI RP and radiated power. Adjusting the phase and locking the frequency of elements for coherent operation are important factors in array architectures, which can be performed through central LO distribution [3] and mutual coupling [4]. LO distribution can cause phase mismatch between elements and significantly increases the DC power consumption by adding more blocks. Mutual coupling through injection locking can maintain phase alignment. However, this type of coupling has low tuning range, which makes it challenging to synchronize elements over a broad frequency range. In this work, a technique for THz CW generation is presented, in which, instead of relying on transistor nonlinearity, a PIN diode is used in the reverse recovery mode for strong harmonic generation. A PIN diode, similar to a step recovery diode (SRD), benefits from a sharp reverse recovery and is highly nonlinear in the recovery mode, which enables efficient THz harmonic generation by upconverting the output of a mm-wave oscillator without requiring additional blocks and multipliers. The PIN-based array consists of 2x3 elements, where differential Colpitts oscillators are used as the core to push the PIN diodes into reverse recovery. Array elements are intercoupled using a collective coupling approach that enables wide tuning range and phase match between elements. The PIN-based array achieves a radiated power of 0.31 mW and 18.1dBm EIRP at 425GHz.