Multiple-Signal Single-Loop Filter (MSSF) sigma-delta modulators

Abstract

This paper presents a new family of Sigma-Delta modulators, the so called Multiple-Signal Single-Loop Filter (MSSF) modulators, where several input signals are added at the modulator input, then passed through only one single loop filter, and converted to digital by means of a column of quantizers, equal in number to the number of input signals. As long as a suitable correction path is added to the input of every quantizer, the input signals are separated at the quantizers' outputs in such a way that they are converted to digital independently of each other. Each quantizer output has the digital version of only one of the input signal plus its corresponding quantization noise shaped by the order of the loop filter. The procedure to achieve the above is explained for a general Sigma-Delta modulator in the ideal case. This paper also studies the performance degradation produced by mismatch in the coefficients of the correction paths. High-level simulations show that the MSSF modulator, even under the effects of mismatch, is a power efficient approach to convert multiple input signals.