Recent research indicates that a direct correlation exists between brain activity and oscillations of the pupil. A publication by Park and Whang shows measurements of excitations in the frequency ...range below 1 Hz. A similar correlation for frequencies between 1 Hz and 40 Hz has not yet been clarified. In order to evaluate small oscillations, a pupillometer with a spatial resolution of 1 µm is required, exceeding the specifications of existing systems. In this paper, we present a setup able to measure with such a resolution. We consider noise sources, and identify the quantisation noise due to finite pixel sizes as the fundamental noise source. We present a model to describe the quantisation noise, and show that our algorithm to measure the pupil diameter achieves a sub-pixel resolution of about half a pixel of the image or 12 µm. We further consider the processing gains from transforming the diameter time series into frequency space, and subsequently show that we can achieve a sub-micron resolution when measuring pupil oscillations, surpassing established pupillometry systems. This setup could allow for the development of a functional optical, fully-remote electroencephalograph (EEG). Such a device could be a valuable sensor in many areas of AI-based human-machine-interaction.
A novel purely VCO-based architecture for a second-order ΔΣ ADC is presented. The proposed architecture achieves in-band second-order quantisation noise shaping. The proposed ADC is highly digital ...and well suited for design in scaled technologies. The architecture has been validated with MATLAB Simulink based models.
In this Letter, an opamp-free noise shaping successive-approximation register (SAR) ADC is proposed. Third-order noise shaping is achieved by implementing a second-order passive filter and a passive ...error feedback topology. In the proposed scheme, the SAR error signals (including quantisation noise, comparator thermal noise, DAC thermal noise and settling error) are subjected to third-order noise shaping. Therefore, the thermal noise specifications of the comparator can be relaxed. Also, since no active element is used, the proposed scheme achieves a higher power efficiency than earlier SAR ADCs.
This Letter proposes an operational-amplifier free with an embedded passive gain technique to implement an oversampling, noise shaping successive approximation register (SAR) ADCs. In the proposed ...scheme, the comparator noise, quantisation noise, settling errors and DAC thermal noise are alleviated. A third-order noise shaping SAR ADC with inserted passive gain design in 40 nm CMOS technology is well suited for low power application because of using passive elements like capacitors and switches. Due to the oversampling and shaping scheme, the structure can be used for high-speed and high-resolution operation.
A novel 0-2 Multi-Stage Noise Shaping (MASH) analogue-to-digital converter (ADC) is proposed. The first stage is implemented using a 4-bit SAR ADC. The second stage uses a voltage controlled ...oscillator (VCO)-based quantiser (VCOQ). Unlike earlier VCOQs which provide first-order noise shaping, the VCOQ proposed in this Letter achieves second-order noise filtering. To implement this noise shaping, the quantisation noise of the VCOQ is extracted as a pulse-width-modulated signal, and it is fed back to the VCO input using a charge pump circuit. In the proposed scheme, the input signal to the VCO is small. Therefore, the linearity requirement of this block is relaxed. Also, any error related to the charge pump circuitry will be first-order shaped at the output. Simulation results confirm the second-order noise shaping of the output of the ADC, and an excellent (14-bit signal-to-noise and distortion ratio) performance with the over-sampling ratio of 16.
The dependence of the noise performance of a 0.6–1.2 V continuous-time delta-sigma modulator (DSM) on its supply voltage is analysed. The noise performance and benchmark figure of merit (FoM) mainly ...depend on the power dissipation, thermal noise contributions from the analogue loop filter, and the quantisation noise from the quantisers. Theoretical estimates for the supply dependence of loop noise and quantisation noise, and their respective FoM are derived and verified with simulations for a 2 MHz third-order continuous-time DSM, while operating from a supply between 0.6 and 1.2 V. At a larger supply voltage, the FoM related to the loop filter noise improves, whereas at lower supplies, the FoM related to the quantisation noise improves. As a result, the overall FoM of the DSM reaches an optimum at a particular supply. The supply voltage with the best FoM of the DSM is derived with the supply-scaling FoM of the loop filter and quantisers. For an equal FoM of the loop filter and quantisers at a supply V$_{\rm DD\comma\;0}$DD,0, the optimal supply voltage is 0.66 V$_{\rm DD\comma\;0}$DD,0.
A low-power delta–sigma modulator based on inverter operational-transconductance amplifiers (OTAs) using correlated level shifting technique (CLS) is presented. The CLS technique boosts the DC gain ...of inverter-based OTA from 42 to 79 dB and extends the linear output swing from 55 to 80% of the full scale. Simulation results show that design in 180 nm CMOS technology, the proposed second-order delta–sigma modulator achieves a signal-to-quantisation-noise ratio improvement of 10.4 dB compared to a conventional inverter-based modulator implementing the identical loop filter with the same oversampling ratio.
This study deals with three-level scalar quantisation of a Gaussian source, followed by Huffman encoder, especially suitable for signal compression purposes. The variance-matched and ...variance-mismatched versions of quantiser are considered. Simple approximate closed-form expressions for performance evaluation in terms of signal-to-quantisation-noise ratio and bit rate are derived using the corresponding Q-function approximations. The accuracy of the derived formulas is tested using the relative error as a measure of performance. It is shown that the derived formulas for variance-matched (for a reference variance) and variance-mismatched (in a wide range of input signal variances) provide higher accuracy in comparison to baselines using other available Q-function approximations or available approximate formulas for non-uniform scalar quantisation of Gaussian source.
In this study, the uplink performance of cell-free massive multi-input multi-output (mMIMO) system with multi-antenna access points (APs) and users is investigated, assuming low-resolution ...analogue–digital converters (ADCs) are employed at the APs. By exploiting the additive quantisation noise model, a tight closed-form rate expression is derived. This tractable finding characterises the impacts of the multi-antenna APs and users, the imperfect quantisation error and the channel estimation error. In order to maximise the uplink sum-rate, a joint quantisation bit and power control problem is formulated, subjecting to the backhaul capacity and each user power constraints. The original resource optimisation problem is non-convex and it is decomposed into two sub-problems, namely quantisation bit design and power allocation problem, to alleviate the difficulties. In particular, the resultant two sub-problems can be efficiently determined by utilising the Lagrange Multiplier and sequential convex approximation methods, respectively. Finally, numerical simulations are presented to examine the analytical findings and evaluate the effectiveness of the proposed algorithm.
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