In this brief, a new low-voltage CMOS circuit to produce current-mode exponential characteristics is proposed. MOSFET transistors in weak-inversion region and translinear principle for the temperature cancellation were used. The functionality of the proposed design confirmed with 0.35 μm CMOS process technology using ±0.75 V supply voltage. Results demonstrate the theoretical analysis and verify the efficiency of the proposed structure compared with previously reported designs. Around 96 linear-in-dB output current range is achieved with ±0.5 dB linearity error over normalized input range from -5.75 to 5.75. The maximum deviation in the output current is ±1.27 and ±3.35 dB due to 100 °C temperature variations and ±10% supply voltage fluctuation, respectively.

A linearization technique of voltage-to-frequency characteristics of voltage-controlled oscillator (VCO) analog-to-digital converters (ADCs) is presented. In contrast to previous works, the proposed technique is an open-loop calibration-free configuration, so it can operate at higher frequencies. It is also independent of the delay element structure, so it can be applied to various VCO ADC topologies. The analog input signal is first mapped through a preweighted resistor network in which every delay element experiences a different version of the input and produces the corresponding delay. As a result, the proposed approach suppresses the impact of V/F nonlinearity on the ADC performance by expanding a linear region of the transfer curve over the full rail-to-rail input. This technique shows substantial improvement results by keeping nonlinearity within ±0.5% over the full input scale (dBFS) and achieves a peak signal-to-noise and distortion ratio (SNDR) of 75.7 and 60.4 dB for input of -8 and 0 dBFS, respectively.

Measuring fluid flow velocity using ultrasonic based sensors has been established for some time, however implementation of this technology in respiratory systems is relatively recent. This paper presents the design of a respiratory flow sensor made possible by the air-coupling ultrasound principle. A prototype has been developed as a proof-of-concept. To enhance the signal to noise ratio (SNR), the modulated ultrasound arrival time is translated to a digital word using Time-to-Digital Conversion (TDC). Hence, the respiration is digitally captured in real-time to offer a synchronous respiratory monitoring. The near-zero deviation is further alleviated by Least Mean Square (LMS) technique accomplished off-line. Down to 0.03 L/s of resolution and over 95% of linearity is achieved. The bidirectional transmit/receive echo signals have been leveraged to provide a system level cancelation of the environmental conditions affecting measurement accuracy. The developed sensor was used on adult volunteers and tested experimentally using an ASL5000 lung simulator. The results validate the system functionality in the presence of real-world conditions.

Analog-to-digital converters (ADCs) based on voltage-controlled oscillators (VCOs) demonstrate superior hardware efficiency. They benefit from the technology scaling; however, they exhibit inferior performance against supply noise. The objective of this work is, therefore, to present a VCO-based ADC architecture with built-in immunity against supply noise. The proposed technique exploits the dynamics of injection locking oscillation in multiphase ring topology. It provides a system-level cancelling of power supply noise, independent of the VCO architecture used in the time-mode ADC. The design functionality has been demonstrated using behavioral and transistor-level simulations using 65nm technology. Under a 10% mismatch of VCO gain and a 128 MS/s data rate, the reported power supply noise rejection (PSNR) improvement is 25 dB, as compared with a typical VCO-based ADC.

A continuous‐time four‐quadrant multiplier in subthreshold region is presented. Besides its simplicity, the structure features inherent process–voltage–temperature (PVT) variation cancellation while working under low voltage supply and dissipating an ultra‐low power. The PVT variation was alleviated through an inherent log/anti‐log cancellation technique, making it as a good candidate for bio‐potential acquisition systems. The input and output signals are currents resulting in a wider bandwidth and larger dynamic range compared with the voltage‐mode counterparts. The circuit is versatile and can be configured as a modulator, frequency doubler, and linear variable gain amplifier as shown in theory and simulation results.