Joint odd-even quantisation in cartesian delta-sigma (ΔΣ) upconverters

Delta-Sigma (ΔΣ) converters enable good in-band signal to quantisation noise performance from coarse quantisers. They achieve this by oversampling the signal and noise shaping the quantisation noise such that it does not fall in the band of interest. We apply ΔΣ techniques to the direct generation of RF modulated signals using two (binary) or three level waveforms, which are pulse width or pulse position modulated. The ΔΣ filters operate on the baseband IQ signals and quantisation is in the polar domain. Two-dimensional quantisation is required and low complexity methods of achieving this are described and compared. The complexity is more than halved if pulse widths are restricted to an even or odd number of clock cycles. This comes at a 5 dB loss in RF signal to noise performance.