Systematic design method for LC bandpass Sigma Delta modulators with feedback FIRDACs

In this paper, a generalized technique for the design automation of fs/4 bandpass SigmaDelta modulators using feedback FIRDACs is proposed. The FIRDACs are used to increase the degrees of freedom in order to perform an exact equivalence with high order discrete-time SigmaDelta modulators and also to allow a more efficient circuit implementation of the LC filter. The design technique is based on discrete time-continuous time equivalence simplified by using the method of partial fractions expansion. The excess loop delay is taken into account without making more difficult the calculations since we define how to get the orders of the FIRDACs. Several examples of design are simulated with different values of excess loop delay.

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