Design Of DAC And Filter In The16Bit Sigma-delta Digital-to-analog Conventer

As the bridge connects the digital world to the analog world, there aretremendous changes have taken place whether on the structural or performance ofDAC since1940s. For the constantly optimized performance of DAC, it hasimportant applications in many fields, such as aerospace, national defense,automotive, electronics consume and so on. The DAC and analog filter in this paperis used in16bit sigma-delta Digital-Analog Converter. The main function isconverted the multi-bit digital signal of modulator to analog signal, and thenfiltered higher harmonics.This paper mainly contains two parts which are the digital circuit and theanalog circuit.The digital circuit is DWA algorithms. It includes: thermometer decoder,4-bitadder and logarithm shift circuit. The main function of it is to achieve the selectionof rotary for unit capacitance and reduce the mismatch errors of capacitance.The analog circuit includes: switched capacitor circuit and the eight-orderButterworth low-pass filter. The timing part of switch-capacitor circuit uses thetwo-phase non-overlapping clock. The filter consists of the classic one that is two-order A-M circuit. It’s-3dB frequency is100KHz and the double cut-off frequencyattenuation is47.86dB.Finally, the paper intergrade all the modules together and get the output rangeof DAC on the ramp wave is6.589mV~4.777V, its DNL is-0.38LSB and INL is-0.46LSB. When the input signal of sinusoidal is100KHz, the clock frequency is5MHz, and then the DAC’s SFDR is90.33dB. To verify the effectiveness of theDWA algorithm, this paper added the mismatch artificially. By comparing thespectrum of filter’s output in the two conditions if the circuit had added the DWAalgorithm, the conclusion is the DWA algorithm does reduce the mismatch errorsand improve performance of the DAC.