Electronic scrambling device

With the rapid development of semiconductor manufacturing technology, the integration and conversion accuracy of various data acquisition systems are getting higher and higher. As a bridge between the analog world and the digital world, the analog-to-digital converter (ADC) plays an important role in the data acquisition system. Therefore, the ADC is required to have higher conversion performance. However, due to various non-ideal factors inherent in the ADC itself, the performance indicators of the ADC are restricted. Dither technology is an external digital calibration algorithm. By adding Dither signal to the input end of ADC, it can effectively improve the harmonics in the spectrum of the quantized output signal of the ADC, thereby improving the performance index of the ADC. This paper theoretically analyzes the source of ADC quantization error and the realization principle of Dither technology. First, the scrambled ADC quantized output signal is multiplied and averaged, and the effect of scrambling on the ADC resolution is studied, and it is found that small-amplitude Dither scrambling can improve the ADC resolution to less than 1LSB. Secondly, the specific relationship between ADC quantization error and input signal is analyzed, and a scrambled ADC simulation model is built under Simulink for testing. The simulation results show that the Dither technique can randomize the correlation between the quantization error and the input signal. Third, the improvement of spectral harmonic distortion caused by ADC coherent sampling, quantization error and differential nonlinearity by Dither technology is studied, and a simulation system is built under Simulink for testing. The results show that Dither technology can effectively improve the harmonic distortion of spectrum. Wave distortion, so that the 8-bit ADC spectrum spurious free dynamic range is improved by about 8dB. In this paper, a typical large-amplitude wideband and large-amplitude narrowband Dither scrambling and descrambling scheme is designed, and its influence on the spurious-free dynamic range of the ADC is studied, and the simulation is carried out under the Simulink simulation platform. The simulation results show that with the increase of the amplitude of the disturbance signal, both scrambling schemes can make the SFDR index of the ADC increase first, then remain unchanged and then decrease. Among them, the large-scale narrow-band Dither scrambling can increase the SFDR of the ADC by about 9.26dB, and the large-scale wide-band Dither scrambling can increase the SFDR of the ADC by about 7.09dB. Afterwards, the theoretical analysis of Dither's de-scrambling was carried out, and the simulation results verified that de-scrambling after scrambling would not deteriorate the signal-to-noise ratio. Aiming at the problem that the amplitude of the scrambled signal is too large and the input signal may exceed the quantization range of the ADC after scrambled, a scheme in which the amplitude of the external Dither changes adaptively with the input signal is proposed. Compared with the reference voltage value, the flag voltage control signal is output, so that the Dither signal will appear the self-adaptive result of alternating positive and negative with the input signal. The simulation test shows that the scheme can effectively control the scrambled input signal within the ADC quantization range, and increase the SFDR of the large-scale narrow-band scramble by about 10dB. In this paper, the hardware verification of scrambling is realized, and the disadvantages of traditional large-scale narrow-band Dither signal hardware are analyzed, and a narrow-band Dither structure based on narrow-band code table storage is proposed. generation of signals. The narrowband Dither signal and the input sinusoidal signal are added by the analog adder to realize the data acquisition of the scrambled signal. Through the spectrum analysis of the collected scrambled digital signal on the PC side, it is found that scrambling can effectively improve the harmonic distortion of the spectrum, and increase the spurious-free dynamic range of the data acquisition system by about 6dB.

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