In this paper we present the practical implementation of a high-speed polyphase sampling and demultiplexing architecture for optoelectronics analog-to-digital converters (OADCs). The architecture consists of a one-stage divideby-eight decimator circuit where optically-triggered samplers are cascaded to sample an analog input signal, and demultiplex different phases of the sampled signal to yield low data rate for electronic quantization. Electrical-in to electrical-out data format is maintained through the sampling, demultiplexing and quantization processes of the architecture thereby avoiding the need for electrical-to-optical and optical-to-electrical signal conversions. We experimentally demonstrate a 10.24 giga samples per second (GS/s), 12-bit resolution OADC system comprising the optically-triggered sampling circuits integrated with commercial electronic quantizers. Measurements performed on the OADC yielded an effective bit resolution (ENOB) of 10.3 bits, spurious free dynamic range (SFDR) of -32 dB and signal-to-noise and distortion ratio (SNDR) of 63.7 dB.
Herein, we apply theoretical models to characterize the transfer function and frequency response of a complex optoelectronic circuit that comprises a primary ultrafast sampling circuit followed by a cascade connection of N demultiplexing stages. The successive radio-frequency optoelectronic samplers were based on the cascade connection of positive-intrinsic-negative-photodiodes (PIN-PDs). We developed a procedure to calculate the principal design parameters that allows us to use optical power for each sampling and demultiplexing stage, such that the circuit can be designed based on the application requirements. The results obtained from the theoretical models were compared with the measurements obtained from the 2.5 GS/s sampling circuit connected in cascade with a 1.25 GS/s and a 625 MS/s demultiplexing circuit implemented using commercial PIN-PDs
In this work we have developed equivalent circuit models for the frequency response of an optically triggered switch based on a positive-intrinsic-negative photodiode (PIN-PD) for the On state (light applied to the PIN-PD) andthe Off state (without applying light to the PIN-PD). From measurements it was found the frequency response in Off state behaves as a high-pass filter whereas in the On state as a low-pass filter; this means that depending on the input signal frequency there could be an approach or even an overlap between the output amplitude in the On and in the Off state. The developed models allow the calculation of the highest permissible frequency in the input signal to avoid distortion due to overlap of the On and Off state response, and the models take into account circuit parameters such as bias voltage, load resistance, resistance, and capacitance of PIN-PD, which in turn depend on the operating point and the desired linear range for the input's amplitude. Experimental measurements of the frequency response were made in both conditions (On and Off state) using three commercial photodiodes of bandwidth higher than 1 GHz. The measured frequency response as well as amplitude separation between the On and Off states to avoid the overlap is very well matched by the calculated results. Although the tests were performed for photodiodes with 1 GHz bandwidth, the technique can be applied for photodiodes with higher bandwidth.
We propose a mandatory invasive mechanical ventilator prototype for severe COVID-19 patients with volume and pressure control operation modes. This system comprises basic pneumatic elements and sensors. Its performance is similar to commercial equipment, and it presents robustness to external disturbances and parametric uncertainties. To develop a control strategy, we propose a mathematical model with a variable structure that incorporates the dead zone phenomenon of the proportional valve, and considers external disturbances and parametric uncertainties. Based on this model, we propose a global control strategy that is based on pressure and flow regulation controllers, which use the active disturbances rejection control structure (ADRC). In this strategy, we propose robust state observers to estimate disturbances and the signals necessary for implementing the controllers. We illustrate the performance of the prototype and the control strategy through numerical simulations and experiments. We also compare its performance with PID controllers. These results corroborate its effectiveness and the possibility of its application in invasive mechanical ventilators with a simple structure, which can significantly help critical care of COVID-19 inpatients.
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