tailieunhanh - Advances in Solid State Part 11

Tham khảo tài liệu 'advances in solid state part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CMOS Integrated Switched-Mode Transmitters for Wireless Communication 291 frequency output power efficiency and linearity requirements. Thus stand-alone PAs have long been manufactured in III-V technologies such as GaAs or GaN or specialized technologies such as LDMOS or SiGe bipolar junction transistors. Largely driven by the drive for integrating more digital functionality on the same chip area CMOS devices have continued to shrink in device dimensions basically following Moore s law. Accordingly transistor ft and fmax are expected to rise to several hundreds of GHz thus allowing for circuit operation in excess of 100GHz Niknejad et al. 2007 . However the trend of shrinking device dimension comes with certain distinct disadvantages for analog circuit design and more specifically for PA design. Due to shrinking oxide thickness the breakdown voltage of the devices is reduced implying that supply voltages must be reduced for safe operation. This has implications for CMOS PAs as the maximum output power assuming load-line matching is then given by Pout Vdd2 2Ri 1 such that in a 500 system and a supply voltage of 1V the output power is limited to 10mW or 10dBm. Thus impedance transformation must be used so that the amplifier sees a lower impedance. This is practically limited to 1-50 Having such a low impedance makes the PA efficiency very sensitive to parasitic series resistance in the output network because of conduction losses A parasitic resistance in series with a load resistance of 10 gives a loss of 10 . Due to these increasing technology limitations in modern CMOS deep-submicron technologies special transistors are provided having a thicker gate oxide and thus allowing for higher supply voltage. Losses in switched-mode amplifiers Looking at RF power amplifiers we want to have an output signal at the frequency of interest - usually the fundamental frequency sometimes a harmonic - but no disturbing output signals at other frequencies. In other words .