Concurrent-Mode CMOS Detector IC for Sub-Terahertz Imaging System

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 degrees phase shift based on common source operation and an inphase 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-mu m mixed-signal 1-poly 5-metal layer CMOS process, where the size, including the pad, is 1.13 mm x 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/root 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.

Automated summary

This paper proposes a CMOS detector for high-quality images in the sub-terahertz region, and verifies its design and performance. By adding a cross-coupling capacitor and using common source operation, the detector improves the output-signal coupling characteristics. The experimental results demonstrate that the proposed detector achieves excellent detection performance at high frequencies, resolving narrower line widths, and achieving a higher signal-to-noise ratio for THz imaging.