This paper proposes a battery-compatible electronic interface based on a general purpose lock-in amplifier (LIA) capable of recovering input signals up to the MHz range. The core is a novel ASIC fabricated in 1.8 V 0.18 µm CMOS technology, which contains a dual-phase analog lock-in amplifier consisting of carefully designed building blocks to allow configurability over a wide frequency range while maintaining low power consumption. It operates using square input signals. Hence, for battery-operated microcontrolled systems, where square reference and exciting signals can be generated by the embedded microcontroller, the system benefits from intrinsic advantages such as simplicity, versatility and reduction in power and size. Experimental results confirm the signal recovery capability with signal-to-noise power ratios down to −39 dB with relative errors below 0.07% up to 1 MHz. Furthermore, the system has been successfully tested measuring the response of a microcantilever-based resonant sensor, achieving similar results with better power-bandwidth trade-off compared to other LIAs based on commercial off-the-shelf (COTS) components and commercial LIA equipment.
This paper presents a low-voltage 3V single supply analog lock-in amplifier (LIA) for processing small AC sensor signals buried in noise, including those presenting a relative phase with respect to the reference signal. Reference and bias sensor signals are provided by a quadrature oscillator. Experimental results confirm the capability of the proposed lock-in amplifier to effectively recover information from signal to noise ratios below 0.025, with an error below 9%.
This Letter presents a capacitive-based sensor system for fingertip contact applications. It is capable of simultaneously measuring normal (pressure) and tangential (shear) stresses at the interface between a fingertip and external objects. This could be potentially exploitable for applications in the fields of upper limb prosthetics, robotics, hand rehabilitation and so on. The system was calibrated and its performance was tested using a test machine. To do so, specific test protocols reproducing typical stress profiles in fingertip contact interactions were designed. Results show the system's capability to measure the applied pressure and stresses, respectively, with high linearity between the measured and applied stresses. Subsequently, as a case study, a 'press-drag-lift' based fingertip contact test was conducted by using a finger of a healthy subject. This was to provide an initial evaluation for real-life applications. The case study results indicate that both interface pressure and shear were indeed measured simultaneously, which aligns well with the designed finger test protocols. The potential applications for the sensor system and corresponding future works are also discussed.
A squaring circuit is introduced that boosts the tail current source of an opamp to improve its slew rate. It operates as a differential voltage magnitude detector, which generates opamp tail currents proportional to the magnitude (square) of the opamp's differential input voltage. Experimental results from a fabricated test chip verify current and slew rate enhancement between 900 and 1400% with respect to its initial value with <20% static current increase.Introduction: Output currents limit the positive and negative slew rates SR + and SR − of class A operational amplifiers (opamps). In one-stage opamps, these are limited by the maximum output currents to a value SR + = I o + MAX /C L and SR − = I o − MAX /C L , where C L is the load capacitance and I o + MAX and I o − MAX are the maximum output currents of the opamp. On the other hand, in two-stage opamps the slew rate can be limited either by the opamp's maximum output current to values SR + = I o + MAX /(C L + C c ) and SR − = I o − MAX /(C L + C c ) or by the maximum current that the first stage delivers to the compensation capacitor C c to values SRI + = I oI−MAX /C c and SRI − = I oI + MAX /C c . Here, C c is the compensation capacitance and I oI+MAX and I oI−MAX are the maximum output currents of the first stage.In this Letter, we report tail current boosted class AB two-stage and folded cascode opamps that use a squaring circuit (SC) as a differential voltage magnitude detector. The SC is based on wide swing cascoded flipped voltage followers (CASFVFs) [1, 2] which allows a current and slew rate enhancement of up to 1400% with respect to its value in the class A configuration with <20% static current increase.
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