Abstract
A CMOS detector with a concurrent mode for high-quality images in the sub-terahertz region has been proposed. The detector improves output-signal coupling characteristics at the output node. A cross-coupling capacitor is added to isolate the DC bias between the drain and gate. The detector is designed to combine a 180° phase shift based on common source operation and an in-phase output signal based on the drain input. The circuit layout and phase shift occurring in the cross-coupled capacitor during phase coupling are verified using an EM simulation. The detector is fabricated using the TSMC 0.25-μm mixed-signal 1-poly 5-metal layer CMOS process, where the size, including the pad, is 1.13 mm × 0.74 mm. The detector IC comprises a folded dipole antenna, the proposed detector, a preamplifier, and a voltage buffer. Measurement results using a 200-GHz gyrotron source demonstrate that the proposed detector voltage responsivity is 14.13 MV/W with a noise-equivalent power of 34.42 pW/√Hz. The high detection performance helps resolve the 2-mm line width. The proposed detector exhibits a signal-to-noise ratio of 49 dB with regard to the THz imaging performance, which is 9 dB higher than that of the previous CMOS detector core circuits with gate-drain capacitors.
Highlights
Terahertz (THz) waves represent frequencies of the 0.1–10 THz bands of the frequency spectrum
The performance of an active system can be expressed by the signal-to-noise ratio (SNR), in which a measurement target is independently placed between a transmitter and a receiver, and the receiver detects and outputs the signal reflected or transmitted from the target
A physical chopper located in the focal plane reduces the flicker noise by transmitting the detected output direct current (DC) voltage along with an alternating current (AC) signal
Summary
Terahertz (THz) waves represent frequencies of the 0.1–10 THz bands of the frequency spectrum. An active full-wave structure is required to develop a safe and high-resolution THz imaging system. The performance of an active system can be expressed by the signal-to-noise ratio (SNR), in which a measurement target is independently placed between a transmitter and a receiver, and the receiver detects and outputs the signal reflected or transmitted from the target. The SNR of the image quality factor can be calculated as the ratio between the output signals when the transmitted signal is reflected away by a metal target and when the transmitted signal passes through a nonreflective target; the reflected transmission output measures the noise of the detector
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