Hani Sherry

A 1kpixel CMOS camera chip for 25fps real-time terahertz imaging applications

Future imaging applications in the submillimeter-Wave range (300GHz to 3THz) require RF systems that can achieve high sensitivity and portability at low power consumption levels. In particular, CMOS process technologies are attractive due to their low price tag for industrial, surveillance, scientific, and medical applications. Recently, CMOS-based detectors have shown good sensitivity up to 1THz with NEPs on the order of 66pW/√(Hz) at 1THz [1]. However, CMOS terahertz imagers developed thus far have only operated single detectors based on lock-in measurement techniques to acquire raster-scanned images with frame rates on the order of minutes [2]. To address these impediments, we present a low-power 1kpixel terahertz camera chip fully compliant with an industrial 65nm ft/fmax=160GHz/200GHz CMOS process technology. The active-pixel circuit topology is designed to accommodate the optics for wide bandwidth (0.6 to 1THz) in stand-off detection with a 40dBi Si-lens. It includes row/col select and integrate-and-dump circuitry capable of capturing terahertz images with video frame rates up to 25fps at a power consumption of 2.5μW/pixel.

25.5 A 320GHz phase-locked transmitter with 3.3mW radiated power and 22.5dBm EIRP for heterodyne THz imaging systems

Non-ionizing terahertz imaging using solid-state integrated electronics has been gaining increasing attention over the past few years. However, there are currently several factors that deter the implementations of fully-integrated imaging systems. Due to the lack of low-noise amplification above fmax, the sensitivity of THz pixels on silicon cannot match that of its mm-Wave or light-wave counterparts. This, combined with the focal-plane array configuration adopted by previous sensors, requires exceedingly large power for the illumination sources. Previous works on silicon have demonstrated 1mW radiation [1,3]; but higher power, as well as energy efficiency, are needed for a practical imaging system. In addition, heterodyne imaging scheme was demonstrated to be very effective in enhancing detection sensitivity [4]. Due to the preservation of phase information, it also enables digital beam forming with a small number of receiver units. This however requires phase locking between the THz source and receiver LO with a small frequency offset (IF<;1GHz). In [5], a 300GHz PLL is reported with probed output. In this paper, a 320GHz transmitter using SiGe HBTs is presented (Fig. 25.5.1). Combining 16 coherent radiators, this work achieves 3.3mW radiated power with 0.54% DC-RF efficiency, which are the highest among state-of-the-art silicon THz radiators shown in the comparison table in Fig. 25.5.6. Meanwhile, the output beam is phase-locked by a fully-integrated PLL, which enables high-performance heterodyne imaging systems.

Real-time video rate imaging with a 1k-pixel THz CMOS focal plane array

Future submillimeter-wave and THz (300GHz-3THz) imaging applications will require low-cost portable systems operating at room-temperature with a video-rate speed and capable of delivering acceptable sensitivity at the very low-power consumption levels to become attractive for truly commercial applications. In particular, CMOS technologies are of interest due to their high integration level offered at a high yield that is capable of massive cost reduction of currently existing THz systems. It has been recently demonstrated that CMOS direct detectors achieve the performance comparable or even superior to the todays existing classical THz devices for active imaging operating at room-temperature. So far, however, only single pixels have been used, allowing only a raster-scan operation. To address this obstacle, we present the very initial work on a 1k-pixel camera chip with a completely integrated readout circuitry and with a full video-rate capability at a power consumption of 2.5μW/pixel. The chip is fully compliant with an industrial bulk CMOS technology and it is intended for active imaging applications. It exhibits a pixel pitch of 80μm, defined by a novel on-chip wire ring antenna, and is designed to accommodate silicon hyper-hemispherical lens for a wide operation bandwidth of at least 0.7-1.1 THz.

5.5 A forward-body-bias tuned 450MHz Gm-C 3 rd -order low-pass filter in 28nm UTBB FD-SOI with >1dBVp IIP3 over a 0.7-to-1V supply

Due to the absence of internal nodes, inverter-based Gm-C filters [1,2] allow achieving bandwidths beyond what is possible with opamp-RC techniques. The class-AB behavior of the inverter, together with the high transconductance for a given quiescent current, results in a high dynamic range for a given power consumption when optimally biased [3]. The major disadvantage of traditional inverter-based Gm-C filters is that they are tuned with the supply voltage, VDD, and hence require a finely controllable supply. Voltage regulators used to accomplish this require a voltage headroom (including margin for tuning) and degrade total power efficiency by tens of percent. In this paper, we show that by exploiting body biasing in an ultra-thin buried oxide (BOX) and body, fully-depleted SOI (UTBB FD-SOI) CMOS technology, we overcome the requirement for a tunable VDD in inverter-based Gm-C filters, while achieving high linearity over a wide supply voltage range.

25.5 A 320GHz subharmonic-mixing coherent imager in 0.13µm SiGe BiCMOS

Terahertz imaging has been gaining increasing attention for its emerging applications in security, biomedical and material characterization. Previous works have demonstrated terahertz imagers on silicon: in [1], the authors demonstrated a 280GHz 4×4 array and an 860GHz pixel using Schottky-barrier diodes; in [2], a 0.7-to-1.1THz 1k-pixel camera was presented. Unfortunately, most previous works are based on incoherent direct detection (Fig. 25.5.1), which causes low sensitivity due to the output droping quickly with input power (∝VRF2), and, as a result, need exceedingly high power sources for illumination. This problem can be alleviated by utilizing coherent heterodyne detection scheme (Fig. 25.5.1), in which the terahertz input (RF) mixes with a local oscillation (LO) signal and generates an output with the amplitude proportional to VRFVLO. As the LO power is normally significantly higher than RF, the sensitivity is much enhanced. Moreover, as the output also carries the RF phase information (φRF), digital beamforming is achievable. For a better comparison, an NPN transistor is configured both as a direct detector (input power injected from the emitter) and a heterodyne detector (-20dBm LO power pumped into the base). The simulated output current with different input power is shown in Fig. 25.5.1, in which we observe a sensitivity enhancement of more than 40dB. However, this coherent sensing scheme introduces a great challenge of synchronizing the frequencies of the transmitter (TX) radiated signal and the receiver (RX) LO. Fortunately, phase-locked terahertz sources have been demonstrated on silicon [3,4]. In this paper, a fully integrated 320GHz high-sensitivity coherent-imaging transceiver chipset is demonstrated.