Recently, wireless power transfer has attracted much attention for power supplying on not only small electric devices but also large equipments such as electric and hybrid vehicles. Coils are important components in such power transfer systems and their AC resistance is a key factor to determine the transferring efficiency. The AC resistance of wires used in the coils is required to be as lower as possible for high efficiency systems. Copper clad aluminum (CCA) wire which has an aluminum (Al) core surrounded by a thin copper (Cu) layer has been proposed for this purpose. CCA wires are not only light-weight and easy for soldering but also show lower AC resistance than commonly used Cu wires on certain conditions. In this paper, the AC resistance caused by the skin and proximity effects of a CCA wire with circular cross-section is numerically analyzed. The condition that CCA wires are superior to Cu wires in view of AC resistance is discussed. Simulated results are compared with experiments on fabricated coils and good agreement is obtained. It is actually verified that coils wound by CCA wires have lower AC resistance than those by Cu wires under some circumstances, especially at high frequencies.

This paper presents a power amplifier (PA) designed as a part of a transceiver front-end fabricated in 130-nm SiGe BiCMOS. The PA shares its output antenna port with a low noise amplifier using a low-loss transmission/reception switch. The output matching network of the PA is designed to provide high output power, low AM-AM distortion, and uniform performance over frequencies in the range of 24.25-29.5GHz. Measurements of the front-end in TX mode demonstrate peak S21 of 30.3dB at 26.7GHz, S21 3-dB bandwidth of 9.8GHz from 22.2to 32.0GHz, and saturated output power (Psat) above 20dBm with power-added efficiency (PAE) above 22% from 24 to 30GHz. For a 64-QAM 400MHz bandwidth orthogonal frequency division multiplexing (OFDM) signal, -25dBc error vector magnitude (EVM) is measured at an average output power of 12.3dBm and average PAE of 8.8%. The PA achieves a competitive ITRS FoM of 92.9.