Behavioral modeling and simulation of mixed signal front-end for software defined radio terminals

Study of implementation issues for software radio terminals needs a wide design exploration to answer to the largest range of specifications. Behavioral modeling is an efficient solution to meet these requirements. This paper describes the modeling and validation of a mixed-signal front-end (MFE) receiver. This front-end consists in an analog-to-digital converter (ADC) closely linked with a digital front-end (DFE). The VHDL-AMS language, used to model analog and mixed parts, allows behavioral modeling in mixed-signal space. Then, it is possible to model and validate with the same language and a single simulation environment the analog and digital parts of a mixed-signal front-end. This paper presents an example to validate the method of analog and mixed-signal system simulation. For this work, a 4-step-process is followed. First, the behavior of the ADC available on a hardware platform is modeled from electrical measurements. Then, the DFE is designed by selecting and scaling digital blocks. These two main blocks are finally simulated jointly to allow DFE improvement according to the fixed constraints of the ADC. The DFE is implemented in the FPGA of the prototyping platform and the behavior of the global system is analyzed. From the qualitative comparison of measurements with simulation results, the validity of the method can be evaluated.