A Systematic Simulation of Large Signal on Chip Amplifier Modules Excited by WCDMA Signals

The exponential growth of the mobile communication market is continuing unabated so that more and more demands are being placed on the available spectrum. This has in turn stimulated the development and deployment of spread spectrum systems based on Code Division Multiple Access, CDMA. This paper addresses problems inherent to the design of large signal gain blocks for use in wide-band CDMA systems. Consistent with our previous work we make use of the Envelope Circuit Simulator in Agilent EDA's Microwave Design System, MDS. The large dynamic range of the CDMA power envelope spectrum, expressed in the crest factor, serves to make simulated harmonic load and source tuning attractive for assessing system performance. The input and output immittances seen by the individual gain blocks must be chosen to satisfy the real time function condition. We demonstrate that simulated results using improperly chosen immittances might lead to incorrect interpretation of large signal behavior of the semiconductor devices. The large fluctuation of the CDMA stimulus tries the linearity of the transfer function leading to spectral re-growth. A study of base-band performance (without harmonics) has shown that the Adjacent Channel Power Ratio, ACPR, is primarily dominated by the derivative of the transfer function with respect to the output power level. The use of pre-correction of the overall transfer function has proved to be the most appropriate means to enhance system performance.