Sigma-Delta -modulator

Yun, W. and R.T. Howe Sigma-Delta Modulator Interfacing with Silicon Micro sensors. Sensors. 11 (May 1993). 

SIGMA DELTA MODULATORS Nonlinear Decoding Algorithms and Stability Analysis, S. 

Park, S. 1990. Principles of Sigma-Delta Modulation for Analog-to-Digital Converters. Motorola, Inc., Phoenix, AZ. 

This is used in the sigma-delta modulator (Fig. 10). In this case, the staircase generator is not needed, since the feedback integration and the input signal integration are performed by the unique integrator after the sum point, and simple 1-bit A/D and D/A do the job. 

The output y of the sigma-delta modulator is low-pass filtered to s with a digital filter and decimated to a much lower output rate with high resolution. For instance, an internal sample rate of 3 X 10 sps and an output data rate of 100 sps may be typical values. 

Higher order architectures have been successfully used to build converters for digital audio applications [Adams, 1986][Hauser, 1991], However, the complexity of modulator and demodulator increases with the order. Higher order architectures also exhibit stability problems [van de Plassche, 1994], Dithering is a remedy to many of the problems of low level signals (see the previous section) and has been used in sigma delta converters as part of the noise shaping loop [Vanderkooy and Lipshitz, 1989]. 

Analog signals can be converted to digital codes by many methods, including integration, successive approximation, parallel (flash) conversion, delta modulation, pulse code modulation, and sigma-delta... 

Modulation-based readout circuits have gained popularity for interfacing with capacitive and inductive MEMS sensors to reduce the noise levels of l// noise and direct current (dc) offset in the circuit. Modulation-based circuits are based on sigma-delta (2A) converter [56,62,65], successive approximation register (SAR) analog-to-digital converter (ADC) [56,66], chopper modulation [54,55,58], pulse-width modulation (PWM) [57,61,63], and frequency modulation (FM) configurations [42,48,51,64,68],... 

There are various opioid receptors the three major classes of opioid receptors are mu (p), delta (5) and kappa (k) receptors. The p, receptor is the principal pain-modulating site in the CNS, mediating the action of morphine. There is considerable interest in the K receptor, which mediates a sedating analgesia with decreased addiction liability and respiratory depression and which allows for some structural flexibility. Unfortunately, the K receptor seems to be coupled to the sigma (a) receptor, which is implicated in psychotomimetic and dysphoric side effects. 

Fig. 3. Spectrum from bandpass delta-sigma modulator (1-bit digitizer) wiUi clock signal at 800 MHz and input signal at 1020 MHz.

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