Papers by Keyword: Sigma-Delta

Abstract: Aiming to be applied in silicon gyroscope, a three-order single loop feedforward modulator with three-bit quantizer and local feedback is designed in this paper. Signal band is 200 KHz, sampling rate is 25.6 MHz, OSR is 64. Ideal modulator is then designed and simulated in MATLAB, getting SNR 125dB. Non-ideal factors are also added to ideal model, DWA technology is adopted to restrain the nonlinearity of multi-bit quantizer, getting SNR 104dB. Finally, transistor-level full-difference modulator is designed and simulated in Cadence, fetting SNR 101.3dB.

Abstract: In this paper, a 16 Bits 500 kHz Sigma-Delta DAC for Silicon Micro Gyroscope is proposedin order to enhance the precision of the digital to analog converter level.The interpolation filterhas achieved 64 times interpolation function,using three cascaded manner, it employs three level cascaded of FIR filterstructure. It achieves a 64 times oversampling feature. The signalbandwidth of the designs interpolation filter is 100 kHz, SNR reach 106dB. Fifth-order single-loop structure CIFB achieve noise shaping modulator function to verify the stability of the system, after the completion of CSD coefficient coding, signal to noise ratio reached 119.7dB, effective bits reached 19.59. The switched capacitor technology actualize analog reconstruction filter module, and using a typically switched capacitor DAC achieved high jump "0, 1" digital signal is converted into an analog signal, the digital-analog conversion achieved.

Abstract: Due to the huge potential applications in military and civil fields, silicon micro mechanical gyro has become the most popular research direction in MEMS field today. Therefore, the corresponding interface circuit of silicon gyroscope has also become a hot topic at home and abroad. Now, integration, digitalization and intelligence has become the focus of future research directions of silicon gyroscope, so the research of analog to digital conversion circuit for gyroscope has become a research priority. Therefore, the conduct of Sigma Delta ADCs research for silicon gyro interface circuit has a very important significance and application prospects.This topic briefly introduces the working principle of Sigma Delta ADC. Based on the requirements of the modulator design, Sigma Delta modulator structures are carefully analyzed and also carried on the comparison and optimization. Hereby, a three order three bits quantization in single-loop with partial feedback of feed-forward summation system structure for modulator is designed in this paper, and then the ideal model of modulator system in Matlab is simulated. In addition, the focus of this topic is mainly on the nonlinear factors analysis and modeling, and the Data Weighted Average (DWA) technique used in multi-bit quantization is introduced as well as modeling in system level. Then, the non-ideal modeling of system is simulated in Matlab.In system level design, this paper adopts feed-forward summation and multi-bit quantization structure to reduce the output of the integrator, increase the noise performance of the modulator, and make it easier for the system stability. Furthermore, the use of partial feedback in the structure for zero-point optimization improves the noise shaping ability in signal bandwidth of modulator. This topic employs the single-loop third-order three-bit quantization structure, with the sampling rate 64, signal bandwidth 200 K Hz and the sampling clock frequency 25.6 MHz. For the ideal modeling, the Signal-to-Noise Ratio (SNR) is 125dB, and the Effective Number of Bits (ENOB) is 20.48. When in consideration of modulator’s nonlinear factors, the nonlinear systems Simulink simulation results obtained SNR of 104dB, and the ENOB is 16.98.In order to reduce the harmonic distortion of the modulator, transistor level is implemented by fully-differential switch capacitor circuit. The structure at all levels of the integrator was optimized. To reduce the influence of flicker noise, the integrator adopts Correlated Double Sampling (CDS) technology, and is improved by the partial feedback circuit. The fully-differential operational amplifier with high slew-rate and high bandwidth is designed, and uses switch capacitor circuit as common-mode feedback. Dynamic comparator and multi-bit quantizer are designed to improve the speed of the quantizer and reduce power consumption. The design the nonlinear compensation feedback DAC module--DWA module circuit--realizes noise shaping of capacitance matching error. The overall circuit was simulated in Cadence by 0.6um process. Transistor-level simulation result shows that the SNR is 101.3dB, and the effective number of bits is 16.54bits. The simulation results are consistent with the established non-ideal model of modulator, which verifies the correction of system level design method.

Abstract: In this paper a high-order sigma-delta modulator applied in micro-accelerometer is designed. The modulator chooses the distributed feedback structure. And the signal bandwidth is 500Hz, the oversampling ratio is 250 and sampling frequency is 250KHz. By the MATLAB Simulink simulation, when the input signal is 1g, and the signal frequency is 250Hz, the simulation result is that the noise level is-160dBV at the signal frequency in the ideal situation. And when considering the non-ideal factors, the simulation result shows that the noise level at the input accelerated signal is 20dBV higher than the ideal. The overall circuit was implemented under 0.5 um CMOS process and simulated in Cadence Spectre. The final simulation results show that the signal to noise ratio (SNR) is 97.1dB.

Abstract: In this paper, in order to enhance resolution and guarantee the stability of the micro-gyroscope, a high-resolution lowpass sigma-delta modulator is proposed. It employs single-loop fourth-order and full differential structure. The simulated result on the Simulink platform shows that the SNDR is 105.4dB and the effective number of bits (ENOB) is 17.22bits. The entire circuits are implemented with 0.5μm CMOS process. The simulated result on Cadence shows that the SNDR is 99.7dB. The modulator operates at a sampling frequency of 25.6MHz and the signal bandwidth is 100kHz with 128 oversampling ratio (OSR). The dynamic range (DR) is 120 dB approximately and the SNDR changes linearly with the input level.

Abstract: Mathematical model of sensitive structures and detection principle of Sigma-Delta accelerometer are analyzed in this paper, and then an accelerometer with SNR 107dB is designed using MATLAB, the stability of which is analyzed based on root locus plot. When input is small than-3dBFS, the system is unsaturated. The poles and zeros of accelerometer noise transfer function are then analyzed and the feed-forward coefficient and local feedback coefficient are optimized, achieving a higher SNR of 112.1dB. At last, the circuit-level simulation is conducted and in-band noise level is about-140dB.

Abstract: In this paper, a 4^th-order sigma-delta modulator applied in gyroscope is presented. This modulator adopts the 2-1-1 Multi stage noise shaping structure. The bandwidth of signal is 100 KHz, the over sample rate is 64, and sample frequency is 12.8MHz. By the MATLAB Simulink modeling and simulation, when the input signal is 100 KHz, the SNDR of the MASH ADC is 121.8dB, and the effective number of bit is 19.93 in ideal situation. After considering non-ideal factors, the SNDR is 111.6dB, the effective number of bit of ADC is 18.28. Compared with the ideal situation, the noise floor of PSD has increased 40dB. It explains that non-ideal factors have a significant effect on the performance of the sigma-delta ADC. The 4^th-order MASH sigma-delta modulator has been implemented under 0.5 um CMOS process and simulated under Cadence. The final simulation results show that SNDR is 112.4 dB and effective number of bits (ENOB) is 18.6.

Abstract: Based on requirements on high performance and high resolution of modulators, a fourth-order Sigma-Delta modulator for audio application is developed in this paper. The modulator is designed under the commercial 0.5μm CMOS process and the circuits are given simulations by Spectre. The sampling frequency of sigma-delta modulator is 11.264 MHz, and OSR is 256 within the 22 kHz signal bandwidth. Measure performance shows that Sigma-Delta modulator enables its maximum SNR to achieve 103.5dB, and the accuracy of Sigma-Delta modulator is up to 16 bit.

Abstract: In this paper a fourth-order single-loop sigma-delta modulator applied in micro-gyroscope is designed. The modulator system chose the fully feedforword structure. The signal bandwidth is 200KHz, oversampling ratio is 64 and sampling frequency is 25.6MHz. By system simulation result in Matlab, the signal to noise ratio (SNR) is 92.3dB and effective number of bits (ENOB) is 15.03bits. The whole circuit of modulator is designed and simulated in Cadence Spectre. It is gotten that the SNR is 78.6dB and changes linearly with input level. When input level is bigger than -4dBFs, the modulator becomes overload.

Abstract: A high-order interface circuit based on sigma-delta (ΣΔ) modulation is advantageous to enhance the resolution and reduce the quantization noise of micro-accelerometer, while the performance is restricted by the effect of nonlinearity of op-amp, electrostatic force feedback and quantizer. A fifth-order closed-loop ΣΔ capacitive accelerometer is proposed in this paper and a theoretic nonlinearity of the accelerometer was investigated. The nonlinear behavioral models based on SIMULINK are given in the paper. The simulation and test result are presented through optimization based on the nonlinearity analysis at last.