A 64-Pixel 0.42-THz Source SoC With Spatial Modulation Diversity for Computational Imaging

This article presents a terahertz (THz) source system-on-a-chip (SoC) specifically designed for computational imaging with a single-pixel camera (SPC). The SoC consists of an 8 x 8 array of independent, frequency-unlocked THz sources that together radiate maximum 10.3-dBm power at 0.42 THz. Each source pixel is composed of a fundamental Colpitts oscillator, followed by a common-collector doubler and an on-chip circular slot antenna. The THz power radiated from the array can be modulated in space by turning the pixels on or off individually with 100% modulation depth. The SoC integrates a dedicated memory space where 64 of such spatial patterns can be stored and triggered externally at up to 10-MHz modulation rate. The spatial modulation can be additionally multiplexed with separate programmable chopping rates for individual pixels. The combined modulation diversity provides a highly reconfigurable THz light projection for SPCs. Furthermore, each pixel also incorporates a built-in power-test (BIST) for an in situ radiation power monitoring and calibration. All of the aforementioned functions are programmable with an integrated application-specific integrated circuit (ASIC) through a standard SPI interface. This integration level readily allows low-cost aperture scaling by combining multiple chips at the board level. The SoC was applied in a compact, 8 x 8 pixel, silicon-only THz SPC that captures transmission-mode images at 25 frames/s with 40-dB voltage dynamic range. With an appropriate receiver and baseband processing, the imaging speed of such SPCs can be extended to thousands of frames per second.