Yongho Oh

The Island-Gate Varactor—A High-Q MOS Varactor for Millimeter-Wave Applications

A new accumulation MOS varactor with island-shaped poly gate layout is proposed to improve the quality factor ( Q-factor) at high frequency, which can be readily employed for CMOS-based millimeter-wave applications. Measured results up to 67 GHz show significant improvements in the Q-factor and the series resistance Rs over the conventional multi-finger MOS varactors with the same ground rule and gate area. The proposed island-gate MOS varactor is expected to improve the overall Q-factor of the LC tank of millimeter-wave oscillators.

A 47 GHz

A 47 GHz LC cross-coupled voltage controlled oscillator (VCO) employing the high-Q island-gate varactor (IGV) based on a 0.13 ¿m RFCMOS technology is reported in this work. To verify the improvement in the phase noise, two otherwise identical VCOs, each with an IGV and a conventional multi-finger varactor, were fabricated and the phase noise performance was compared. With VDD of 1.2 V and core power consumption of 3.86 mW, the VCOs with the IGV and the multi-finger varactor have a phase noise of -95.4 dBc/Hz and -91.4 dBc/Hz respectively, at 1 MHz offset, verifying the phase noise reduction with the introduction of the high-Q IGV. The VCO with IGV exhibited an output power of around -15 dBm, leading to a FoM of -182.9 dBc/Hz and a tuning range of 3.35% (45.69 to 47.22 GHz).

LC

This paper presents a comprehensive study on the high-Q island-gate varactor (IGV), which includes a comparison with the conventional multifinger varactors (MFVs) and analyses on the effect of structural variations on the varactor performance. The study shows that the IGV exhibits smaller Rs and larger Q factor compared to the MFV, while its capacitance tuning ratio is smaller. The effect of the dimension variation and shape of the gate island, as well as the gate thickness, is substantial and the observed trends can be exploited for IGV optimization. This work indicates that the IGV is a highly promising option for millimeter-wave applications.

Cross-Coupled VCO Employing High-

The impact of digital noise coupling through the substrate on RF MOSFETs was investigated in terms of the noise figure (NF) of the device up to 26.5 GHz. Previous works on the substrate digital noise coupling have treated the effect mostly in terms of the electrical isolation between ports, rather than actual devices, which does not provide direct information on the degradation of actual device performance parameters from such coupling. In this work, an actual NMOSFET was employed for test and the effect was described in terms of NF, a practical device performance parameter. The results show that NF is significantly degraded as the device enters the weak inversion state and/or V ds becomes smaller, suggesting a trade-off between low power operation and immunity against the substrate noise coupling. Also, it is experimentally verified that devices with a dual guard ring showed much smaller NF than those with a single guard ring.

Q

Challenges in the implementation of THz circuits based on Si-based technologies such as Si CMOS and SiGe HBT technologies are overviewed in this paper. Major challenges described in this work include the operation speed of Si devices, loss of Si substrate, model accuracy, uncertainty in EM simulation, and the presence of dummy patterns. Possible techniques to partly circumvent the challenges are also discussed. A review of recently reported Si-based circuits operating beyond 100 GHz is provided.

Island-Gate Varactor for Phase Noise Reduction

Noise figure (NF) formulas are presented for RF MOSFETs in the presence of digital substrate noise. When the digital substrate noise is much higher than the intrinsic MOSFET noise, simplified NF formulas can be obtained. For the case of which the digital substrate noise is comparable to the MOSFET thermal noise in magnitude, general NF expressions of RF MOSFETs with digital substrate noise are derived. Comparisons of the derived NF formulas and the experimental results are done showing good agreement between them for RF MOSFETs with digital substrate noise.

A Comprehensive Study of High-

In this letter, the variation in the key RF performance parameters of MOSFETs in the presence of the substrate digital noise coupling is investigated. The parameters, including fT and fmax, showed substantial change up to ~20% with realistic level of noise injection. It is shown that such change in the RF performance with the noise injection is due to the threshold voltage ( VT) variation. The observed VT variation is attributed to the virtual body effect due to the substrate potential fluctuation by the coupled substrate digital noise.