# A Magnetic-Balanced Inductive Link for the Simultaneous Uplink Data and Power Telemetry  
[PERSON]  
1 Institute of Application Specific Instruction-Set Processors, Beijing Institute of Technology,  
5 South Zhongguancun Street, Haidian District, Beijing 100081, China; [EMAIL_ADDRESS] (C.G. ); [EMAIL_ADDRESS] (Z.M. ); [EMAIL_ADDRESS] (M.L.) 1  
[PERSON]  
1 Institute of Application Specific Instruction-Set Processors, Beijing Institute of Technology,  
5 South Zhongguancun Street, Haidian District, Beijing 100081, China; [EMAIL_ADDRESS] (C.G. ); [EMAIL_ADDRESS] (Z.M. ); [EMAIL_ADDRESS] (M.L.) 1  
[PERSON]  
1 Institute of Application Specific Instruction-Set Processors, Beijing Institute of Technology,  
5 South Zhongguancun Street, Haidian District, Beijing 100081, China; [EMAIL_ADDRESS] (C.G. ); [EMAIL_ADDRESS] (Z.M. ); [EMAIL_ADDRESS] (M.L.) 1  
[PERSON]  
1 Institute of Application Specific Instruction-Set Processors, Beijing Institute of Technology,  
5 South Zhongguancun Street, Haidian District, Beijing 100081, China; [EMAIL_ADDRESS] (C.G. ); [EMAIL_ADDRESS] (Z.  
systems ([PERSON] _et al._, 2016; [PERSON] _et al._, 2017; [PERSON] _et al._, 2018). The LSK transmits the uplink data by switching the load impedance of the implant coil to induce detectable current variations on the external coil. However, the load switching could substantially affect the wireless power transmission (WPT). The load switching may decrease the power transfer efficiency (PTE) and cause large voltage ripples on the implant load. To reduce the impacts of the load switching on the WPT, some new LSK methods are proposed ([PERSON] _et al._, 2016; [PERSON] _et al._, 2018). However, these new LSK methods rely on close coupling (\(k\) = 0.5\(\sim\)0.2) and can hardly achieve reliable transmission under weak coupling. To achieve reliable uplink data transmission under weak coupling, a new modulation method was recently proposed in ([PERSON] _et al._, 2018), named passive phase shift keying (PPSK). The fundamental aspect of PPSK is similar to LSK. It transmits the uplink data by shorting the implant coil at a specific period to induce larger current variations on the external coil. However, the short connection of the implant coil could also cause larger voltage ripple on the implant load. To both enhance the reliability under ultra-weak coupling and reduce the impact of the uplink data transmission on WPT, a dual-carrier inductive link scheme is proposed in ([PERSON] _et al._, 2018). In this scheme, dual carriers are used for the power and uplink data transmissions through the same coil pair. It achieves reliable uplink data transmission under ultra-weak coupling without causing significant loss of PTE or ripple on the implant load. However, because the power carrier and the uplink carrier are both transferred through the same coil pair, the external receiver suffers severe power carrier interference. The ratio of signal-to-interference (SIR) could be as low as \(-\)75.79 dB. To avoid such severe interference, researchers once proposed to use multiple coil pairs to separate data links from the power link ([PERSON] _et al._, 2018; [PERSON] _et al._, 2018; [PERSON] _et al._, 2018). They designed a perpendicular structure ([PERSON] _et al._, 2018) and an overlapped structure ([PERSON] _et al._, 2018) for both the implant part and the external part to reduce the cross-coupling between the power coils and the data coils. However, these methods requires multiple implant coils. The extra implant coil will increase the surface footprint and bulk volume of the implant biomedical sensor devices, which renders the multiple coil-pair method unusable for the biomedical sensor devices on certain areas of the body. To reduce the additional surface footprint of the implant, the figure-eight structure ([PERSON] _et al._, 2018) is further proposed. The figure-eight data coils are put inside the power coils. However, it is also unusable for certain areas of the body due to its special structure.