Shielding effectiveness of noise coupling on Analog-to-digital converter in magnetic field wireless power transfer system

Abstract

The radio frequency interference (RFI) problems are critical issue for communication devices. Among the components of the communication devices, the Analog-to-digital converter (ADC) is one of the important device which is related to the RFI problems, because of two reasons: one is that it is difficult to decouple the coupled noise after converting to the digital signals by ADC, and the other is that the ADC is becoming of utmost importance in not only communication systems but also automotive systems. With the increased number of magnetic field sources near the ADC that can alter its behaviors significantly, we need to know how magnetic field affects the performance of ADC, and how it could be shielded. In order to accurately evaluate the performance of ADC, the accurate expectation of noise coupling with consideration of shielding material is essentially required. In this study, we use the inductive transmission line model (I-TLM) method for evaluating the performance of ADC with magnetic field [1]. The I-TLM includes three separate sub-models: a model of the magnetic field coupling from the input of magnetic field source to the PCB feeding signal of ADC with or without shielding material, a model of the noise coupling from the PCB to the ADC input, and a model of the ADC behavior from the PCB input of ADC to the digital outputs of ADC. By using the model, the shielding effectiveness of shielding material is fast and accurately expected. The considered shielding material is ferrite, graphene, and copper, the trend of shielding effects are related to the material characteristic. The device under test (DUT) comprise the WPT coil, which is the targeted magnetic field source, and ADC which is fabricated using a 0.13 µm complementary metal-oxide semiconductor (CMOS) process and is wire-bonded to the designed PCB for ADC.