Image Number 4 for United States Patent #5764171.
A receiver including two sigma delta modulators used to convert a pair of analog quadrature signals into digital quadrature signals. In such sigma delta modulators the quantization noise is shifted into a frequency region in which no signal is present. A cross coupling between the filters is provided to improve the noise reduction without increasing the order of the filters. By providing the cross coupling, it is possible to obtain complex poles and zeros in the noise transfer function which do not have to appear in complex conjugate pairs which results in an increase of the noise suppression in a specified frequency range.