5.8GHz ETC SiGe-MMIC Transceiver having Improved PA-VCO Isolation with Thin Silicon Substrate

A fully integrated SiGe-MMIC transceiver having a power amplifier (PA), a transmit/receive switch (T/R SW), and a voltage controlled oscillator (VCO) is developed for electric toll collection system (ETC) terminals. To improve the isolation between the PA and the VCO, the back-polish technique of the silicon substrate (127mum thickness) is employed. Electro-magnetic simulation shows that a MMIC of 127mum thickness achieves the isolation improvement of 12.3dB compared with that of conventional 300mum thickness. As a result, the USB/LSB unbalance of the transmitted amplitude shift keying (ASK) signal can be reduced from 4.2dB to 1.2dB at 13dBm output power. The MMIC transceiver fabricated in 0.35mum SiGe BiCMOS process achieves the maximum output power of 15.5dBm with the adjacent channel power ratio (ACPR) of -33.5dBc