Should {\Delta}{\Sigma} Modulators Used in AC Motor Drives be Adapted to the Mechanical Load of the Motor?

We consider the use of {\Delta}{\Sigma} modulators in ac motor drives, focusing on the many additional degrees of freedom that this option offers over Pulse Width Modulation (PWM). Following some recent results, we show that it is possible to fully adapt the {\Delta}{\Sigma} modulator Noise Transfer Function (NTF) to the rest of the drive chain and that the approach can be pushed even to a fine adaptation of the NTF to the specific motor loading condition. We investigate whether and to what extent the adaptation should be pursued. Using a representative test case and extensive simulation, we conclude that a mild adaptation can be beneficial, leading to Signal to Noise Ratio (SNR) improvements in the order a few dB, while the advantage pushing the adaptation to the load tracking is likely to be minimal.Comment: Sample code available at http://pydsm.googlecode.co

Noise Weighting in the Design of {\Delta}{\Sigma} Modulators (with a Psychoacoustic Coder as an Example)

A design flow for {\Delta}{\Sigma} modulators is illustrated, allowing quantization noise to be shaped according to an arbitrary weighting profile. Being based on FIR NTFs, possibly with high order, the flow is best suited for digital architectures. The work builds on a recent proposal where the modulator is matched to the reconstruction filter, showing that this type of optimization can benefit a wide range of applications where noise (including in-band noise) is known to have a different impact at different frequencies. The design of a multiband modulator, a modulator avoiding DC noise, and an audio modulator capable of distributing quantization artifacts according to a psychoacoustic model are discussed as examples. A software toolbox is provided as a general design aid and to replicate the proposed results.Comment: 5 pages, 18 figures, journal. Code accompanying the paper is available at http://pydsm.googlecode.co

Coding of Stereo Signals by a Single Digital {\Delta}{\Sigma} Modulator

The possibility of using a single digital {\Delta}{\Sigma} modulator to simultaneously encode the two channels of a stereo signal is illustrated. From the modulated stream, the two channels can be recovered with minimal processing and no cross-talk. Notably, demultiplexing does not affect the sample-depth so that, after it, one still has a data stream suitable for directly driving a power bridge and convertible into analog by mere low-pass filtering. Furthermore, the approach is very flexible and if one channel is unused, it lets the other get improved dynamic range and SNR. The approach can take advantage of recent techniques for the design of {\Delta}{\Sigma} modulators, including methods for psychoacoustically optimal distribution of quantization noise. Code is available to replicate the proposed examples and as a general computer aided design tool.Comment: 4 pages, 5 figures. Pre-print from conference proceeding

Output Filter Aware Optimization of the Noise Shaping Properties of {\Delta}{\Sigma} Modulators via Semi-Definite Programming

The Noise Transfer Function (NTF) of {\Delta}{\Sigma} modulators is typically designed after the features of the input signal. We suggest that in many applications, and notably those involving D/D and D/A conversion or actuation, the NTF should instead be shaped after the properties of the output/reconstruction filter. To this aim, we propose a framework for optimal design based on the Kalman-Yakubovich-Popov (KYP) lemma and semi-definite programming. Some examples illustrate how in practical cases the proposed strategy can outperform more standard approaches.Comment: 14 pages, 18 figures, journal. Code accompanying the paper is available at http://pydsm.googlecode.co

Towards a nearly optimal synthesis of power bridge commands in the driving of ac motors

The synthesis of low depth command streams for power bridges is considered, with regards to drives for ac motors. Focus is on the exploitation of the degrees of freedom still available once the command rate is set. Using a nonlinear motor model, different options are evaluated up to the mechanical output. Options such as Delta Sigma Modulation (DSM) and Pulse Width Modulation (PWM) are associated to tuples of merit factors defining points in a performance space. Standard DSM is shown to favor perceived drive quality, while PWM helps keeping the switching rate low. Interpreting both PWM and DSM as heuristics for Pulse Density Modulation (PDM), it is shown that DSM may offer some commonly unexploited forms of tuning and may lead to a more flexible choice of placement on the performance space