Quantization Noise Reduction Techniques for Digital Pulsed RF Signal Generation Based on Quadrature Noise Shaped Encoding

The digital generation of pulsed radio frequency (RF) signals based on noise shaped encoding in complex baseband is a popular concept in digital RF transmitters. However, as the pulsed complex-baseband signals are up-converted to an RF frequency, a conjugate image overlaps with the signal band, which complicates the center frequency tuning for the transmitters in question. In this paper novel ways related to equalization techniques used for imbalanced digital complex valued systems are presented to mitigate conjugate image noise. Firstly, the distortion generation mechanism of the digital up-conversion is explained. Based on the analysis two cancelation techniques are derived. Secondly, novel quadrature encoder topologies implementing the given compensation techniques are developed. The analytical and the simulation based results show conjugate quantization noise suppression of more than 50 dB, which extends the potential center frequency tuning range considerably. Finally, a comparison with previously given encoders reveals nearly 10 dB improvement in dynamic range.