A circuit based behavioral modeling of Continuous-Time Sigma Delta modulators

In evaluating continuous-time sigma delta (¿¿) modulators, the generation of highly accurate results requires long simulation time due to the nonlinear nature of the system. In most cases, a compromise has to be made to trade off precision for speed. This paper presents a circuit-based high level model implemented in the MATLAB SIMULINK environment so as to achieve a faster speed of simulation. Designed in a differential manner, the model provides good visualization of the actual circuit at the early stage of design. To maintain simulation accuracy, circuit nonidealities such as system clock jitter, integrator noise, opamp finite gain, bandwidth and slew rate as well as the digital to analog converter (DAC) mismatches are included in the model. For demonstration purpose, a 4
^th
order CT ¿¿ modulator with NRZ (Non-Return to Zero) architecture is implemented. With the proposed models, key design specifications for the functional building blocks are derived.