VII. Conclusion This article presented a combined inductive power and data transfer system. For best results, the system specification was jointly defined which makes this system unique. Through this holistic approach the mutual interference could be minimized and therefore all other systems could be outperformed. The coupled power coils are used as channel for both signals. The power is transferred using a switching frequency of 500 kHz and can provide 20 W to the load with an efficiency of 86.0%. The data communication system can be integrated without changes into common IPT systems. The needed circuitry for a proper channel separation was shown. This allows the use of the frequency band below 125 kHz, 0 −10 −20 −30 −40 −20 0 20 40 Frequency (kHz) (a) Power Spectral Density (dBm) Power Spectral Density (dBm) that a large spread between power delivery and frequency exists. The performance of the power transfer matches most of the other systems. The communication parameters also significantly vary but no clear trend or standard technique sticks out. It can be seen that this system outperforms all other systems with a significantly higher data rate. Only [40] reached comparable dimension but needed to add an additional communication coil. Without changing the IPT system only rates of 100 kbit/s were reached by sending in non-switching periods or 19-20 kbit/s for continuous transmission. Compared to current research results, this article does not only match the transmission rates but furthermore measured its robustness in terms of EVM and BER, which is a key factor for evaluating and comparing communication standards. 0 −10 −20 −30 −40 −20 0 20 40 Frequency (kHz) (b) Figure 15. Normalized received baseband spectrum with (a) IPT off and (b) on. which in addition would also cover the specification of the CENELEC A and B band. With theoretical derivation it was shown that the possible frequency band for the data transmission in existing IPT systems can be estimated. For demonstration, data was transmitted using OFDM at a carrier frequency of 70 kHz and an effective bandwidth of 96 kHz. For this transmission mode a data rate of 461 kbit/s at an SFDR of 25.11 dB and an EVM down to 1.68% was reached. These performance parameters offer a very solid and interference tolerant communication as a BER of smaller than 10 -5 was measured. Also the communication system does not affect the power transmission. Compared to the state of the art, this system reaches a significantly higher data rate. Furthermore it is the first system which states link quality parameters like EVM and BER to describe the robustness. Table III. Comparison with previous publications. Ref. Comm. Technology Power Delivery Power Frequency Data Carrier Bidirectional Comm. Cont. Comm. Data Rate [19] Mod. of load 5W 110-205 kHz 2 kHz − + 2 kbit/s [22] Mod. of inverter freq. n/a 50 kHz 10-11 MHz − − 100 kbit/s [37] Mod. of inverter volt. 5W 6.78 MHz − − − n/a [38] Extra coil 10 W 150 kHz 4 MHz + + 19.2 kbit/s [26] Extra coil 5W 50 kHz n/a + + 0.25 kbit/s [39] Extra coil 1000 W 100 kHz 1 MHz + + n/a [40] Extra coil 20 W n/a 13.56 MHz + + 411 kbit/s [41] High comm. freq. n/a 50 kHz n/a + − 100 kbit/s [42] High comm. freq. n/a 10-40 kHz 450 kHz + + 19.2 kbit/s [43] High comm. freq. 500 W 22.4 kHz 1.67 MHz + + 20 kbit/s [44] High comm. freq. 250 W 39-47 kHz 15 MHz + + 19.2 kbit/s [25] Low comm. freq. 3000 W 150 kHz 8 kHz + + 1 kbit/s This work Low comm. freq. 20 W 500 kHz 70 kHz + + 461 kbit/s THIRD QUARTER 2019 IEEE CIRCUITS AND SYSTEMS MAGAZINE 31