0.3 THz CMOS Transceiver Pixels for Reflection Mode Active Imaging


December 2022


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Electromagnetic waves at frequencies ranging from 0.1 to 10THz, commonly referred to as THz waves have a wide variety of medical, security and industrial imaging applications. However, generation and detection of signals at these frequencies are quite challenging. The complementary metal-oxide semiconductor (CMOS) technology which is widely used in most of the modern consumer electronic devices is an affordable means for generation and detection of THz signals. Near-millimeter-wave and terahertz imagers are expected to complement visible light, IR, Radar and Light Detection and Ranging (LiDAR) imaging by providing a unique combination of angular resolution and a capability to image in visibly impaired conditions such as fog, rain and dust as well as for imaging through other materials. This research aims at the design of concurrent transceiver pixels operating at frequencies around 300GHz for reflection mode active imaging using a CMOS process technology. A 7-element array of 287-GHz CMOS transceiver pixels with pixel area smaller than (λ/2)2 housed in a QFN package is demonstrated. Each pixel concurrently performs transmission and coherent detection using a push-push VCO, that functions as a 287-GHz transmitter, a 143-GHz LO, and a sub-harmonic mixer at the same time. An effective isotropic radiated power (EIRP) of −2.5dBm and sensitivity of −88dBm for 1-kHz noise bandwidth are achieved. Link budget analyses suggest that it should be possible to perform reflection-mode active imaging at 10 m using the array, and a reflector with a diameter of 15-cm and a simulated near-field gain of 44.6dB. The packaged array exhibits a 2.5-dB higher EIRP and a 3-dB lower noise figure than the array without QFN packaging due to the antenna performance enhancement. This demonstrates that it is possible to package 300- GHz integrated circuits with an on-chip patch antenna using a low-cost technique. Lens-less short-range reflection-mode imaging through cardboard is demonstrated at 275GHz using a pair of concurrent CMOS transceiver pixels separated by ~5mm on a PCB. An isolation study employing EM simulations is performed to quantify the unwanted coupling. This is first such demonstration at frequencies above 100GHz. The separation between the imaged object and pixels is ~1cm and the operation at 275GHz allows the lateral resolution to be reduced to ~2mm due to a smaller wavelength. This pixel achieves an EIRP of -18.9dBm and a double-sided noise figure (NFDSB) of ~51dB in an area of 0.45×0.49 mm2. An 1x3 array of 296-GHz CMOS concurrent transceiver pixels incorporating circuits for baseband signal extraction in addition to the RF section in an area of (λ/2)2 is demonstrated. The EIRP of array is ~-6dBm and NFDSB is ~48dB. An E-shaped patch antenna to broaden the antenna bandwidth is used. Using a pair of these arrays, lens-less short-range reflection-mode imaging of a target ~1cm away through a cardboard is demonstrated. More importantly, use of the arrays improves isolation between the pair by ~10 dB to ~70 dB compared to that when single pixels are used. This work points to a path for incorporation of millimeter and sub-millimeter wave imaging capabilities in a handheld device.



Engineering, Electronics and Electrical