DC Offset Voltage Research Articles

Pretilt‐angle control of liquid‐crystal alignment by using projections on substrate surfaces for dual‐domain TN‐LCD

Abstract— It was found that the value of the pretilt angle of liquid‐crystal alignment achieved by a rubbing technique increases when small projections are present on the substrate surface. A dual‐domain TN‐LCD with very small dc offset voltage across the LC layer was realized by utilizing triangular‐shaped projections.

Circuit techniques for reducing the effects of op-amp imperfections: autozeroing, correlated double sampling, and chopper stabilization

In linear IC's fabricated in a low-voltage CMOS technology, the reduction of the dynamic range due to the dc offset and low frequency noise of the amplifiers becomes increasingly significant. Also, the achievable amplifier gain is often quite low in such a technology, since cascoding may not be a practical circuit option due to the resulting reduction of the output signal swing. In this paper, some old and some new circuit techniques are described for the compensation of the amplifier's most important nonideal effects including the noise (mainly thermal and 1/f noise), the input-referred dc offset voltage as well as the finite gain resulting in a nonideal virtual ground at the input.

Evidence for unpinned magnetic flux vortices above theI ctransition in the 2223-phase high-T csuperconductor

A similarity in the dc voltage-current (V-I) curves for both direct and alternating transport currents is used to propose that unpinned flux vortices are generated above theI ctransition for dc transport currents, when Abrikosov flux vortices begin to penetrate the superconductor. Two methods can be used to give a dc voltage drop for an ac transport current: (1) if there is a slight dc offset voltage in the ac current which favors vortex loop collapse as in a traditional dcI ctest, or (2) if an asymmetric transverse magnetic field is present which favors vortex loop collapse for current in one direction over the reverse direction.

A MODFET-based optoelectronic integrated circuit receiver for optical interconnects

The design, fabrication, and characterization of a 0.85- mu m sensitive photoreceiver is described. The monolithically integrated optoelectronic receiver is based on pseudomorphic InGaAs on GaAs modulation-doped field-effect transistors (MODFETs) and metal-semiconductor-metal (MSM) photodetectors. High-performance quarter-micrometer MODFETs with f/sub t/'s of approximately 70 GHz are utilized in a two-stage transimpedance amplifier. An asymmetric and a symmetric amplifier design are compared. The symmetric design is found to provide the desired zero DC offset voltage for a variety of supply voltages. Excess MSM-detector dark current and low-frequency internal gain are greatly reduced through the use of a silicon passivation layer and/or AlGaAs cap layer. Receiver transimpedances between 100 and 5000 Omega are obtained by varying the bias on an active feedback resistor. The parasitic capacitances of this common-gate feedback FET are studied. A transimpedance amplifier bandwidth as high as 14 GHz and an overall photoreceiver bandwidth of 11 GHz are measured.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Phased array control using phase-locked-loop phase shifters

The work investigates the use of phaselocked loops (PLLs) as phase shifters in the control of a phased antenna array. The phase error of a PLL can be altered by adding a DC offset voltage to the output of the phase detector. If a digital phase detector, with its inherently linear response, is used, then the phase error, and hence the relative phase shift, will vary linearly with applied control voltage. Such phase shifters can act on their own at VHF or they can provide an IF reference signal to a mixer to create a linear phase shifter at microwave frequencies. Four prototype phase shifters, fed in series, have been built, driving a linear array of four monopoles, in transmit mode at 1.5 GHz. By use of a single common control voltage, a single main beam can be swept through 180° with an accuracy of better than±2° within the range±70°.

Mass Transfer Requirements for Alternating Polarity, Alternating Voltage Synthesis

Operation of electrosynthesis reactors with 60 Hz transmission power modulates the electrode potential as a sine wave with no dc offset voltage. Alternating polarity alternating voltage (APAV) describes the synthesis because an electrode changes polarity every half cycle. In APAV electrosynthesis, products from electrode reactions must be removed from the electrode to prevent back reaction and loss of net current efficiency before the next half‐cycle. An experimental study was made of the bromine current efficiency in the indirect electrosynthesis of alkene oxides. Reduction of soluble electrogenerated bromine at polarity reversal decreased the current efficiency for the production of bromine. High mass transfer, rapid homogeneous reaction, and low current density conditions produced high bromine current efficiencies. Bromine current efficiency was correlated as a function of three dimensionless numbers incorporating the homogeneous reaction rate constant, mass transfer coefficient, frequency, average current density, and exchange current density. A mass transfer criterion predicted process conditions required to produce bromine at 95% current efficiency. The correlations were applied to determine the suitability of a candidate chemical pathway for APAV electrosynthesis. Electrogenerated species in direct and indirect syntheses can be produced at 95% current efficiency with above 5.6. Electrogenerated species in indirect syntheses with rapid homogeneous reactions can be produced at 50 to 95% current efficiency with .

Modulation of a gated ion channel admittance in lipid bilayer membranes

A future class of amperometric biosensors may utilize gated ion channels such as acetylcholine and glutamate receptors as chemical detection components. In this study, bilayer lipid membranes containing voltage-dependent anion channels (VDAC) were used to model an ion-channel-based biosensor which could continuously monitor AC amperometric changes resulting from induced changes in channel conductance. The in-phase and quadrature components of the induced alternating membrane current were monitored as a function of the applied DC offset voltage which was superimposed on the sinusoidal test voltage. The accuracy and sensitivity of the AC-measured VDAC response was dependent on the magnitude of the AC test voltage relative to the DC offset necessary for channel closure. The VDAC channel appears to be a suitable model protein for AC impedance-based biosensor fabrication.

Techniques for the determination of left ventricular mass by signal-averaged electrocardiography

The standard ECG correlates poorly with LV mass. The SAECG precisely measures myocardial energy and may allow more exact noninvasive assessment of LV mass. A commercially available system (Corazonix Predictor I) was tested for its ability to reproduce and measure known input energy in square wave and QRS waveforms, using frequency bandwidths different from those used for late potential analysis. A test group of 15 patients was studied to determine optimum filter type and bandwidth for comparison of SAECG energy measurement versus LV mass as determined by echocardiography (Penn conversion) and LV hypertrophy via standard ECG criteria. The best means of energy measurement were maximum and total RMS voltage and the integral of the area under the QRS curve. Optimum correlation with echocardiography was seen with a bidirectional bandpass filter of 5 to 250 Hz applied either to the vector sum of the three orthogonal leads or to the Z lead alone ( r values 0.61 to 0.73), which was equal to or superior to standard ECG LV hypertrophy determinants. A second group of 20 patients was studied prospectively to confirm these findings, which yielded similar results. Conclusion: (1) the SAECG when appropriately modified serves as a rapid noninvasive assessment of LV mass. (2) These modifications must examine the entire duration and energy spectrum of the surface ECG and not just the region of late potentials. (3) Very low frequencies (below 5 Hz) must be excluded to eliminate the energy present due to DC offset voltage.

Compensating for Light Soaking Effects in Optically Addressed Spatial Light Modulators Incorporating A-Si:H Photodiodes

ABSTRACTWe characterize the effects of light soaking on optically addressed spatial light modulators (OASLMs) incorporating a-Si:H photodiodes and relate these effects to the light-induced degradation observed in the photodiodes. After illuminating the OASLMs with white light for up to 100 hours, the rise time of the OASLM optical response decreases, the fall time increases, and the undesirable modulation in the absence of write light (electrical modulation) also increases. We were able to compensate for these effects and approximately restore the original optical transfer characteristics by applying a dc offset voltage across the device. The results can be interpreted by considering series resistance changes in the a-Si:H photodiode.

Switched-capacitor ladder filters with offset-insensitive time-continuous feedback integrators

The possibilities of designing high-order switched-capacitor (SC) ladder filters which are insensitive to the DC offset voltage and at the same time guarantee that all operational amplifiers operate permanently in their active region are investigated. The proposed circuit technique is based on an offset-insensitive fully differential topology, where all operational amplifiers are maintained in the active region by time continuous feedback capacitors. The damping introduced by these additional capacitors leads to a lossy SC ladder filter. A comparative example between a lossless and a lossy 5th-order allpole ladder filter is given in terms of Monte-Carlo sensitivity simulation, showing how the suggested technique can show similar performances. The effect of the finite operational amplifier DC gain on the frequency response of the lossy SC ladder filters can be compensated by the use of a simple predistortion method. The technique seems to be attractive for GaAs technology, where real operational amplifiers can put serious limitations on monolithic analogue designs.

Design Optimization Case Studies

Designing high quality products at low cost is an economic and technological challenge to the engineer. A systematic and efficient way to meet this challenge is a new method of design optimization for performance, quality, and cost. The method, called “robust design,” has been found effective in many areas of engineering design. In this paper, the basic concepts of robust design will be discussed and two applications will be described in detail. The first application illustrates how, with a very small number of experiments, highly valuable information can be obtained about a large number of variables for improving the life of router bits used for cutting printed wiring boards from panels. The second application shows the optimization of a differential operational amplifier circuit to minimize the dc offset voltage by moving the center point of the design, which does not add to the cost of making the circuit.

The electronic pantograph: amplifier couples microscope stage to X-Y plotter

A system is described that allows the X-Y movement of a microscope stage to be coupled to the movement of the pen of a X-Y plotter. Linear potentiometers are displaced by any X- or Y-axis movement of the microscope's stage and are connected to a DC amplifier which provides a varying DC voltage to the inputs of a X-Y plotter. The pen of the X-Y plotter becomes yoked to the movement of the stage and it is possible to draw or count the image that is being viewed at magnifications which are independent of those used for observation. The coupling DC amplifier provides a DC offset voltage at all gain settings of the pantograph which is sufficient to reposition the pen of the X-Y plotter in the center of the plotter's platen, regardless of the location of the specimen on the microscope slide. The electronic pantograph overcomes the limitations of a camera lucida, and is well suited for analyzing connectional neuroanatomical material with bright- and darkfield, polarized light or florescent illumination at a reasonable price and without the complexity and hardware requirements of a computerized system.

Offset-compensated bilinear SC filter of leapfrog type using a two-phase clock

A bilinear switched-capacitor filter realisation of leapfrog type is proposed, which is compensated for the DC offset voltage of the amplifiers. By using offset-compensated integrators in combination with unity-gain buffers, a filter can be realised which operates with a two-phase clock. The realisation is parasitic-insensitive.

Radio frequency magnetron sputtering of radio frequency biased quartz on a scanning pallet

The microstructure and step coverage of silicon dioxide was studied with respect to its use as a planarization layer. The bonded 37.75×12 cm SiO2 target and the 31×31 cm pallet were independently driven by two rf amplifiers using a common exciter. A sliding rf contact was made to the pallet. Target power was fixed at 2.5 kW while rf induced dc offset voltage at the pallet was varied between 0 and 120 V negative on different runs. During each scan the dc offset voltage at the pallet was kept constant, and hence, the rf power to the pallet was increased when it came in front of the denser magnetron target plasma. The average film growth rate was 800 Å/min. The argon pressure in the system was varied between 5.3×10−1 to 2 Pa. It was observed that ion bombardment during film growth, when bias is used, eliminates the columnar morphology and nodular growth and results in SiO2 films that approach the quality of those grown thermally. Such films provide good step coverage for planarization.

Design techniques for dynamic range improvement in CMOS circuitry

Circuit design techniques that improve the dynamic range of signal processing circuitry are discussed. These techniques use differential processing techniques to minimize the effect of correlated and low-frequency noise sources (including feedthrough from power supplies) and dc offset voltage.

Improved offset-compensation schemes for switched-capacitor circuits

Novel switched-capacitor stages which are free from the effects of op-amp DC offset voltage are described. The op-amps used in the stage need not slew between the desired output voltage and the offset voltage as in previously described offset-free circuits. The use of the new scheme in general applications is also discussed.

Scanning MeV-ion microprobe for light and heavy ions

The University of Oregon scanning ion microprobe uses a 65 cm focal length plasma lens to form 8.65 × demagnified image of an object aperture. The plasma lens focuses a positive ion beam using the self-electric field of a trapped cylindrical column of electrons of density 3−9 × 10 9 cm −3 and length 13–18 cm. Since the focusing field is electric, the focal length depends only on ion accelerating voltage and not on ion mass or charge state. Our 5 MV Van de Graaff accelerator illuminates the object aperture with a current density of ∼ 0.5 pA/mu;m 2. The lens aperture is defined by a set of slits 3.35 m beyond the object aperture slits and 2.79 m from the lens. Four pairs of deflection plates are located between the intermediate aperture and the lens. Two pairs of plates are used for each scanning direction so the beam always passes through the lens center during rastering. The 1 kV operational amplifiers that drive these plates combine three sets of signals. Computer generated voltages raster the beam. Individual dc offset voltages align the beam with the lens axis. A small 60 Hz signal cancels the effects of background 60 Hz magnetic fields along the beam line. With 1 kV rastering voltage the rastered field at the focal plane is 3 mm square for 3 MeV ions. Focal spot size is now 10 μm with a 2 mm diameter lens aperture and 5 μm with a 0.5 mm lens aperture.