Digital Filter Design For Sigma-Delta Converter

Sigma-Delta A/D D/A converter is a kind of high-solution converter which uses oversampling techniques, and it is widely used in audio signal application. Digital filter is the important part in Sigma-Delta converter. The digital filter design is the determining factor of the chip area and the power consumption in the Sigma-Delta converter.The paper introduces the digital filter design for 16bit solution Sigma-Delta converter that the oversampled factor is 64. The paper comprises four parts.The first part discusses oversampled converter theory and its advantage comparing with conventional Nyquist-rate converters. Then it introduces the structure of the Sigma-Delta modulator and the structure for 16bit solution Sigma-Delta converter.The second part introduces the multi-rate digital signal processing theory which is used in the digital filter design. Then it discusses two high- efficiency digital filter structures which are CIC digital filter and half-band digital filter, and proposes the digital filter structures for Sigma-Delta converter.The third part discusses the circuit structure for digital filter, and proposes low power CIC filter structure, the operation element re-using structure and CSD multiplicator structure which are saving chip area and power consumption. The fourth part presents the results of Matlab Simulation, Verilog simulation and FPGA validation. Then it discusses the ASIC implementation.Low power CIC filter structure can save half of the power consumption comparing with traditional CIC filter structure. Using FIR halfband filter structure can save half of hardware and power consumption. By using the operation element re-using structure, the FIR filter only needs two multiplicators and four adders, saving lots of hardware. And CSD multiplicator can save 30% hardware. So the digital filter structure is well suitable for ASIC implementation.Using Matlab simulates digital filter circuit system, and using modelsim simulates verilog code. Then using FPGA validates the function of the circuit. The digital filter circuit satisfies 16bit solution Sigma-Delta converter.