While previous studies on substrate coupling focused mostly on noise induced through drain-bulk capacitance, substrate coupling from planar spiral inductors at radio frequency (RF) via the oxide capacitance has not been reported. This paper presents the experimental and simulation results of substrate noise induced through planar inductors. Experimental and simulation results reveal that isolation between inductor and noise sensor is less than 030 dB at 1 GHz. Separation by distance reduces coupling by less than 2 dB in most practical cases. Practical examples reveal an obstacle in integrating RF tunedgain amplifier with sensitive RF receiver circuits on the same die. Simulation results indicate that hollow inductors have advantages not only in having a higher self-resonant frequency, but also in reducing substrate noise as compared to conventional inductors. The effectiveness of using broken guard ring in reducing inductor induced substrate noise is also examined.

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An extremely high Q monolithic inductor (Q>2000) on silicon substrate was reported recently [I]. The reported Q is 3 order of magnitude higher than previously reported monolithic inductor [2]. Such high quality "factor may greatly improve the performance of monolithic RF circuits. In this paper, both I -Port (one terminal at ground) and 2-Port (no terminal at ground) scattering parameters of the high-Q inductor were compared to examine m y possible differences in device characteristics. A broadband physical model of the active inductor on silicon are presem'ed to illustrate the improvement of quality factor. A design space with a range of gain and phase difference of current in the coils of the active inductor is reported. A typical application of the active inductor in CMOS RF power amplifier design is shown to illustrate the feasibility of applying the active inductor in RF circuits design.

Recently, m u c h s t u d i e s have b e e n d o n e t o inc l u d e on-chip inductors for wireless c o m m u n i c a t i o n IC design. T h e large a r e a m e t a l plane of t h e spiral i n d u c t o r can f o r m large capacitor t o t h e silicon s u b s t r a t e . A t high e n o u g h frequency, excitation of t h e i n d u c t o r will induce noise t o t h e s u b s t r a t e . In t h i s p a p e r , we will present t h e simulation results of t h e coupling effect of a p l a n a r spiral i n d u c t o r on heavily a n d lightly d o p e d s u b s t r a t e by using a c o m p a c t m o d e l of t h e s u b s t r a t e . Results show t h a t t h e insertion of a P+ diffusion g u a r d ring can r e d u c e a b o u t 1 5 d B of noise for lightly d o p e d s u b s t r a t e a n d 7 d B of noise for heavily d o p e d s u b s t r a t e at 3GHz. Variation in t h e size of t h e P+ diffusion g u a r d ring affects t h e efficiency of noise reduction a n d also t h e inductance. Results show t h a t in o r d e r t o optimize for inductance, t h e side length of t h e g u a r d ring needs t o b e twice t h e side length of t h e i n d u c t o r a n d t h e g u a r d ring can only r e d u c e a b o u t 6 d B of noise for lightly d o p e d s u b s t r a t e a n d 1.5dB of noise for heavily d o p e d s u b s t r a t e at 3GHz.