Research On Data Acquisition Technology Based On Digital-analog Mixed Scramblingand De-interference

With the rapid development of semiconductor manufacturing process,the integration and conversion precision of all kinds of data acquisition systems are becoming higher and higher,Analog-to-digital converter(ADC)is a bridge between analog and digital worlds,which plays an important role in data acquisition systems,Therefore,ADC also requires higher conversion performance.However,due to various inherent non-ideal factors in the ADC,the performance of the ADC is limited.Dither technology is an external digital calibration algorithm.By adding a Dither signal to the input of the ADC,the harmonics in the frequency spectrum of the ADC's quantized output signal can be effectively suppressed,thereby improving the performance of the ADC.This paper theoretically analyzes the source of ADC quantization error and the realization principle of Dither technology.Based on this,it focuses on the three aspects of Dither technology to improve ADC performance index.First,the influence of Dithering on the resolution of ADC is studied by means of multiple super position and averaging of the scrambled ADC quantized output signals,It is found that small amplitude Dither scrambling can increase the resolution of ADC to less than 1LSB.Second,the specific relationship between the ADC quantization error and the input signal is analyzed,and an ADC quantization simulation model is built under Simulink to test the impact of s Dithering on the ADC quantization error.The results show that Dither technology can randomize the correlation between quantization error and input signal.Thirdly,the improvement of spectrum harmonic distortion caused by three different aspects of ADC's coherent sampling,quantization error and differential nonlinearity is studied,the simulation system was built under Simulink for testing,It was found that the Dither technology improved the spurious free dynamic range of the 8-bit ADC by about 8d B.Two typical large amplitude wideband and large amplitude narrowband Dither scrambling and disturbing schemes are designed to study their effects on ADC's spurious-free dynamic range,and simulation is implemented under the Simulink simulation platform.The simulation results show that with the increase of the amplitude value of the Dither signal,both scrambling schemes can make the SFDR indicator of ADC show the trend of increasing first and then decreasing.Among them,the large amplitude narrow band Dither increases the SFDR about 9.26 d B of the ADC,and large amplitude wideband Dither increases the SFDR about 7.09 d B of the ADC.A theoretical and simulation analysis was performed on the deserption of Dither.It was found that descrambling after scrambling did not deteriorate the signal-to-noise ratio.Aiming at the problem that if the amplitude of scrambling signal is too large and the input signal may exceed ADC quantization range after scrambling,an adaptive scheme of external Dither amplitude with input signal is proposed.This scheme compares the input signal with the reference voltage value set in the high-speed comparator,and outputs the flag voltage control signal,so that the Dither signal has an adaptive result of alternating positive and negative signals with the input signal.The simulation test shows that this scheme can effectively control the Dither signal within the ADC quantization range and increase the SFDR for large amplitude narrow-band scrambling by about 10 d B.Scrambled hardware verification is implemented.The shortcomings of traditional large amplitude narrowband Dither signal hardware are analyzed,a narrow band Dither structure based on narrowband code table storage is proposed,and the timing verification of large amplitude narrow band Dither signals is completed in hardware environment.Adding a narrow-band Dither signal and an input sine signal by an analog adder,Write Verilog code to achieve the collection of scrambled data signals,Through the spectrum analysis of the scrambled digital signal collected by the PC,it is found that the scrambling can effectively improve the harmonic distortion caused by the quantization error and increase the spurious-free dynamic range of the data acquisition system by about 6d B.