Substrate Noise Coupling Through Planar Spiral Inductor

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 30 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.