Design Of Continuous-time Sigma-Delta Modulator

In today's electron systems, the ADC which is the bridge between analog and digital realm is a critical important part. The Sigma-Delta ADC is a kind of new converter which can reach quite high precision, low requirement on analog circuit and voltage source and is convenient to integrate on a chip with digital circuit. For which it has been widely studied and applied increasingly. The basic technology of the Sigma-Delta ADC is oversampling and noise shaping. And on the basis of traditional discrete structure, the continuous-time Sigma-Delta ADC which uses continuous-time integrator and multi-bit feedback technology can replace the pipelined structure in the high-speed and high-resolution field with much less power consumption.A continuous-time Sigma-Delta ADC applied in the medical electronics image systems which require high-resolution image is implemented in this paper. And its design skill and hardware circuit are the key research. First, the principle and the typical application are presented. And then the system module is setup under the system requirement with the simulink toolbox in MATLAB. The finite gain-bandwidth and the non-ideal clock are taken into consideration. After that the coefficients are scaled for circuit implement. The simulation of the system module will guide the circuit design and make it easier. At last, a modulator with 5MHz signal bandwidth and an ENOB of 14 are achieved and meet the design goal. The creative works of this paper include: a newest continuous-time Sigma-Delta structure is proposed; the sampling rate reaches to 320MSPS; the signal bandwidth get 5MHZ with the ENOB of 14 which can be used in the medical electronics image systems as the chip-level processing ADC; an ultra-low power consumption of 19.8mW relative to the pipelined structure; an new CMFB circuit is implemented for the high gain-bandwidth amplifier with a common phase margin about 90°to keep the common-mode stable.