Finite Word Length analysis and design Of digital automatic gain control system for mobile TV applications

The Finite Word Length (FWL) design is an essential step from the system to the digital logic design. In this paper, a digital automatic gain controller (DAGC) used in digital mobile TV receiver is discussed. The effects of A/D quantization error, rounding-off error caused by multiplication and truncation error due to FWL are analyzed for the purpose of efficient FWL designs. The performance is reflected by some parameters such as the dynamic range, stability, accuracy of static state value and time constant. Considering that the system is nonlinear, a method which can be called as Static State with Tiny Fluctuation Equation is introduced to obtain the system transfer function. In addition, a measure of time constant for digital system is also proposed. The proposed analysis methods and results are verified by the computer simulations. The methods discussed in this paper are also applicable to other digital feedback systems.