Study On The ΣΔADC And Digital Decimation Filter

In the variable methods to achieve the ADCs,∑△A ADC is widely used in the audio and electronic measurement for its advantages of the high resolution, good linearity and easy integration with the digital systems. The high resolution achieved by conventional Nyquist-type A/D converters is limited by the matching precision of components, so it is very difficult to achieve high resolution with this kind of A/D converters in the standard CMOS technology. Employing the oversampling and the quantization noise shaping techniques,∑△ADC can effectively reduce the quantization noise in the band of the signal and improve the SNR greatly, in a result, it is possible to achive the high-precision Analog/Digital converters with the low-precision converters. Compared to the Nyquist-type ADC,∑△ADC reduces the matching requirements of the high precision component and moves the pressure of improving the the accuracy to the digital processing portion.∑△ADC mainly is composed of two parts including the analog modulator and the digital decimation filter. On the base of the analysis of the basic principles of∑△ADC, the digital decimation filters are designed and one of the the appropriate archietectures is selected for the battery meausurement in this paper. Meanwhile we need to consider the requirements of the battery measurement system:(1)Multi-channel monitoring; (2) low-cost, low power, high accuracy; (3) The input singal is very low-frequency near to DC. In this design, the dither method is adopted to sharply reduce the flat-zone in the measurement of the low-frequency signal near to DC with the smaller cost.In this design, the voltage channel and temperature channel have 0～5v measurement range and 12-bit resolution, current channel has -64mv～64mv meashurement range and 14-bit resolution. The Vangard 0.5um process was used in the chip's manufacture and the test results verified that the ADC's performance meets the design's specification.