CMOS RF Circuit Design for Reliability and Variability by Jiann-Shiun Yuan

Author:Jiann-Shiun Yuan
Language: eng
Format: epub
Publisher: Springer Singapore, Singapore

5.3 Dual-Band VCO

The explosion of portable wireless communication services results in the demand of multiband and multimode transceivers. Dual-band VCOs play an important role in dual-band transceivers required for multifunction services. The stress effect on dual-resonance VCO was studied [22]. The VCOs were designed and fabricated in the TSMC 0.18 μm 1P6 M CMOS technology. At V tune2 = 0 V, the dual-band VCO operates between 7.86–8.28 GHz at high band and 3.16–3.58 GHz at low band. The VCO transits from its first high parallel resonance frequency to its second low resonance frequency around V tune1 between 0.6 and 0.7 V. The dual-resonance VCO was stressed at V DD = 3 V, V tune1 = 0 V, and V tune2 = 0 V for 1.5 and 3 h. After each stress period, the VCO property is measured again at different lower V DD. High supply voltage increases the gate and drain voltage swings of switching transistors, and hot carrier injection occurs while the output voltage swing is high and the channel electric field is high. When a conventional NMOS is DC biased at maximum substrate current (V GS ≅ 0.5V DS), the hot carrier damage is associated with the creation of interface states [23]. When the nMOSFET is biased at maximum gate bias (i.e., V GS = V DS, condition for hot electron injection), electron traps are created. At low V GS (conditions for hot-hole injection), neutral electron traps are created. During the high V DD stress carried out in the dual-band VCO, the VCO experiences different damage mechanisms [24]. The final dominant mechanism will shows its effect on the device characteristics and circuit performance. The hot carrier damage is localized while the circuit performance is a lumped effect of the overall nonuniform device damage. The dual-resonance VCO is sensitive to hot carrier stress as the hot carrier stress may cause the frequency band shifting out of the original design specification. The stressing also increases device current noises and leads to the increase in the phase noises at both high band and low band.

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