Title :
Analysis of Non-Uniform Polar Quantisers in a Sigma Delta Transmitter Architecture
Author :
Bassoo, Vandana ; Linton, Lance ; Faulkner, Michael
Author_Institution :
Sch. of Innovative Technol. & Eng., Univ. of Technol.-Mauritius, Pointe-aux-Sables, Mauritius
Abstract :
The drive signals for radio frequency switch mode amplifiers can be directly generated by digital circuits using pulsewidth modulation and pulse position modulation. The quantisation noise that occurs when the pulsewidths are quantised to the timing grid can be shaped using sigma delta (ΣΔ) modulation combined with polar quantisation. This paper analyses the behavior of the resulting non-uniform polar quantisation and predicts the signal to noise ratio (SNR) performance of both Cartesian and polar filtered ΣΔ architectures. Practical measurements and simulations support the analysis. Orthogonal frequency division multiplexing and wideband code division multiple access signals are shown to have an increasing SNR with signal strength of 0.5 dB/dB at low signal levels, and 1 dB/dB at medium signal levels prior to entering the overload region. The schemes trade-off improved quantiser fidelity for higher oversampling requirements. They have reduced transitions, better coding efficiency and generally outperform the traditional band-pass ΣΔ scheme. Their complexity grows linearly with the number of quantisation points.
Keywords :
OFDM modulation; code division multiple access; pulse position modulation; pulse width modulation; quantisation (signal); radio transmitters; radiofrequency amplifiers; sigma-delta modulation; ΣΔ modulation; Cartesian filtered ΣΔ architectures; SNR performance; band-pass ΣΔ scheme; digital circuits; drive signals; nonuniform polar quantiser analysis; orthogonal frequency division multiplexing; polar filtered ΣΔ architectures; polar quantisation; pulse position modulation; pulsewidth modulation; quantisation noise; radiofrequency switch mode amplifiers; sigma delta modulation; sigma delta transmitter architecture; signal strength; signal-to-noise ratio; timing grid; wideband code division multiple access signals; Noise measurement; Pulse width modulation; Quantization; Radio frequency; Sigma delta modulation; Noise-shaping; OFDM; RF transmitters; Sigma Delta modulation; non-linear quantisation; pulse width modulation; radiofrequency amplifiers; up-conversion;
Journal_Title :
Circuits and Systems I: Regular Papers, IEEE Transactions on
DOI :
10.1109/TCSI.2012.2206469