| Sigma-Delta conversion technology is based on oversampling, noise shaping, and decimation filtering. There are many inherent advantages in S-D based analog-to -digital converters. The major advantage being that it is based predominantly on digital signal processing, hence the cost of implementation is low and will continue to decrease. Also, due to its digital nature S-D converters can be integrated onto other digital devices. Manufacturing technology notwithstanding, S-D technology offers system cost savings because the analog anti-aliasing filter requirements are considerably less complex and the sample and hold circuit is intrinsic to the technology due to the high input sampling rate and the low precision A/D conversion. Since the digital filtering stages reside behind the A/D conversion, noise injected during the conversion process, such as power-supply ripple, voltage-reference noise, or noise in the ADC itself, can be controlled. Also, S-D converters are inherently linear and don't suffer from appreciable differential non-linearity, and the background noise level which sets the system S/N ratio is independent of the input signal level. The last, but certainly not least, consideration is cost. Attaining a high level of performance at a fraction of the cost of hybrid and modular designs is probably the greatest advantage of all. In this paper, a complete analog front end for low frequency measurement applications is presented. The part can accept low level input signals directly from a transducer and outputs a serial digital word. It employs a sigma-delta conversion technique to realize up to 97dB of no missing codes performance. In part 1, the basic concept of the CMOS opamp is discussed,as well as the design of Switched-Capacitor filters. In chapter3, the fundamental principles of SDM design are given. In part 2, SDM design and the SPICE simulation result are presented. In the end, the layout design are shown. |
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