Differential Photodiode Research Articles

Electrical characteristics of silicon differential photoreceivers

The volt-ampere curve of silicon differential photodiodes were measured. It was found that the current-voltage curve of the photodiodes of the main and additional channels had a similar shape, without revealing a significant dependence on the implantation dose of the additional channel. The main parameters of the equivalent circuits of photodiodes are determined. In the reverse branch, the dominant impact was exerted by the surface leakage conductivity with a differential resistance of about 10 GΩ. Measurements from minus 60 °C to 60 °C showed that when using amplifiers with an input impedance of about 103 Ω, differential photoreceivers can be successfully used as selective short-wavelength and two-color ones.

Synthesis of a new 1,3,4-thiadiazole-substituted phenanthroimidazole derivative, its growth on glass/ITO as a thin film and analysis of some surface and optoelectronic properties

A novel phenanthroimidazole derivative with p-type conductivity was prepared and fabricated as a heterostructure, exhibiting a negative differential resistance and photodiode properties.

Maxwell stress excitation of wire vibrations at difference and sum frequencies of electric currents in separate circuits.

Oscillating electric currents through a wire under tension can excite transverse vibrational modes of the wire when a perpendicular static magnetic field is present and the frequency of the current is close to the natural frequency of the mode of interest. The excitation of the mode is associated with temporally oscillating Maxwell stresses on the wire, often also known as oscillating Lorentz forces. That excitation process is sometimes demonstrated in educational contexts. The investigation here concerns situations where a temporally oscillating magnetic field generated by oscillating electric currents in a cylindrical coil replaces the imposed perpendicular static magnetic field. The frequencies of the currents in the wire and in the coil are related to the frequency of the oscillating stress. In this experiment, this effect is documented for sum-frequency excitation (with input frequencies in the range of half that of the excited lowest vibrational mode of the wire) and the difference-frequency excitation (with input frequencies an order-of-magnitude larger than the mode frequency). This coupling may be useful when it is desirable to use only high-frequency currents. The experiment uses tone-burst stress excitation and a differential photodiode for detecting transverse low-amplitude wire oscillations. Signal envelopes decayed exponentially after the tone-burst.

High-Sensitivity Optical Receiver Using Differential Photodiodes AC-Coupled with a Transimpedance Amplifier

High-Sensitivity Optical Receiver Using Differential Photodiodes AC-Coupled with a Transimpedance Amplifier

High-performance fully differential photodiode amplifier for miniature fiber-optic gyroscopes.

Electrical cross coupling is regarded as a major obstacle to achieving high-performance miniature fiber-optic gyroscopes (FOGs), because it can cause dead bands, which are critical errors in FOGs. Using a differential photodiode amplifier has proven to be effective in rejecting coupled interference. However, the conventional three-op-amp instrumentation amplifier cannot provide a miniature FOG's bandwidth requirements, because of the large photodiode capacitance and parasitic capacitance. We present a high-performance, fully differential photodiode amplifier, where the bandwidth limitations are removed by applying a reverse bias to the photodiode and replacing the feedback resistor with a modified tee-network and a DC cancellation loop. For an experimental FOG with a 300 m fiber coil, we demonstrate a fully differential photodiode amplifier with 880 kΩ gain and 3.5 MHz bandwidth. In the FOG performance test, it not only reduces the angular random walk and bias drift, but also eliminates the approximately 1°/h dead band observed in the same FOG using a PINFET receiver, demonstrating its effectiveness in suppressing coupled interference.

Detection of the Spontaneous Action Potentials of HEK 293 Cells by Prussian Blue thin Films

The gold standard for investigating neuronal electrical activities has been electrodes. Modern electrophysiology methods boast high sensitivity and temporal resolution with the ability to measure single ion channels and networks of neurons. However, the spatial resolution and robustness are limited by the size and geometry of the electrode. In this era, optical methods have picked up momentum as powerful tools to measure the electrical activities of neurons by using an optical probe that transduces the electrical signal into an optical signal. Prussian blue (PB) is a mixed-valence inorganic material composed of alternating ferric and ferrous ions in a cubic, cyano-bridged lattice with open sites for alkaline metal intercalation. This material is known for its biocompatibility, insolubility in water, activities toward alkaline metal ions and electrochromicity. It is the latter property that makes Prussian blue an excellent candidate to measure the electrical potentials of excitable membranes. The color of this material depends on the applied electrical potential which in turn controls the redox state of the irons. Its blue color is turned to colorless by reduction and is recovered by oxidation. We hypothesize that the electrical potential of excitable membranes will modulate the spectral properties of the material which will be detected through a differential photodiode detector. A PB thin film was electrodeposited onto an ITO-coated glass slide and its optical properties were characterized. As a model for electrophysiology measurements, a clone line of modified HEK 293 cells that stably express Nav 1.3 and KIR 2.1 and generate spontaneous electrical action potentials were used. Herein, we demonstrate the ability to detect the extracellular action potentials of HEK 293 cells and evaluate the film's potential for imaging networks of neuronal cells.

Spectral sensitivity of a differential photodiode in a bipolar integrated circuit

We consider the spectral characteristics of an integrated differential photodiode in a bipolar integrated circuit for which the depth of the photosensitive region is limited by the depth at which the buried layer is located in the substrate, while one of the p-n junctions is covered with a standard filter blocking visible radiation. We show that it can be used as a light intensity sensor.

High-Speed Optical Receivers With Integrated Photodiode in 130 nm CMOS

The design and measurement of two optical receivers with integrated photodiode in 130 nm CMOS is presented. The low bandwidth, which is typical for photodiodes in CMOS technologies, is circumvented by a differential photodiode topology on the one hand and by including an optimized equalizer in the receiver chain on the other hand. The low responsivity of a CMOS photodiode is compensated by a very low-noise design for the differential TIA. The disadvantage of such a low-noise design is its high power consumption. Therefore, a design strategy is presented where part of the circuit is biased in weak inversion. Doing so, the power consumption is decreased from 138 mW for the standard design to only 74.16 mW. Both designs are measured optically with 850 nm modulated light and are able to operate at 4.5 Gbit/s with a BER lower than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> . The sensitivities for this BER and speed are - 3.8 dBm and -3.4 dBm respectively. The receivers even work up to 5 Gbit/s for BER values around 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> .

Optimised equaliser for differential CMOS photodiodes

An optimised equaliser to enhance the bandwidth of differential photodiodes, integrated in a standard CMOS technology, is presented. This way, the speed performance of those photodiodes is improved. The advantage over an equalised single-ended photodiode is discussed. Finally, the measured frequency response of a 0.18 μm CMOS equaliser is shown.

Analytical characterization of SOA-based optical pulse delay discriminator

Semiconductor optical amplifier (SOA)-based optical timing extraction and clock-recovery schemes offer compact size, low operating power, and added possibility for integration into an all-optical circuitry. In this paper, we analyze a device that could measure the relative delay between counterpropagating pulses incident on an SOA. Unlike previous designs based on differential photodiodes, our optical pulse delay discriminator (OPDD) uses the voltage difference between two contacts on the SOA. We therefore eliminate the two photodiodes and two optical couplers, making integration far easier. After giving a qualitative description of the operation of the proposed design, we carry out a comprehensive analytical analysis of the operation of the device performance. At each stage, we demonstrate the accuracy of the derived approximate formulas. An analytical expression for the transient response of OPDD shows it to be exponential with a time constant set by the carrier-recovery lifetime. We show that it is possible to reliably measure the incident delay between counterpropagating, periodic pulse trains by measuring the mean value (or low-pass-filtered value) of the induced voltage difference. Our analysis shows the OPDD has excellent linearity.

Reduced component count optical delay discriminator using a semiconductor optical amplifier-detector

Cross-gain modulation between pairs of counter-propagating pulses within a semiconductor optical amplifier is used as a pulse delay detector. Unlike previous designs based on differential photodiodes, the difference between average powers of the pulse trains after propagation are deduced from the voltage difference between two contacts on the SOA, eliminating the photodiodes and two optical couplers. Simulations show the design can be improved by adding a third contact. The linearity, sensitivity and noise performance of the design equal or surpass the original design.

Telescopic refractive index gradient diagnostic of an ion diode anode plasma

We present a general analysis of possible variants of refractive index gradient (RING) diagnostics with a laser beam probe. Using a differential bicell photodiode as a detector, the sensitivity, dynamic range, and geometric restrictions of RING deflectometry have been found for lensless, one lens, and “three-telescope” optical schemes. The three-telescope method is found to be the most flexible and easily aligned. If the refracted/deflected laser beam cross section in the back focal plane of the output lens is also recorded using a fast framing camera, measurements of the beam deflection and its spatial frequency spectrum after passing through the refractive medium can be obtained simultaneously. A general relation is presented between the Fourier transform of a Gaussian beam by the output lens and the spatial frequency spectrum of the inhomogeneities. From these considerations, we present the specific design of a RING diagnostic for study of anode plasma evolution in a magnetically insulated ion diode on the Cornell Beam Research Accelerator (COBRA) (800 kV, 80 ns pulse). The maximum density gradient was found to be located about 0.4 mm from the anode surface at the peak of the diode voltage pulse. The electron density at this position was about 2×1015 cm−3. The transverse spatial frequency distribution of the probe laser beam after passing through the anode plasma was recorded using the optical Fourier transform technique. This experiment demonstrates that the combined integrated deflection. (RING) and Fourier transform optical techniques can give a great deal of information about this thin (∼1 mm) anode plasma layer.

Laser-ultrasonic measurements of thin-film properties using surface acoustic waves

High-frequency, laser-ultrasonic methods to evaluate the mechanical properties of thin films have been developed. The approach is based on the optical generation and detection of surface acoustic waves (SAWs) to determine the frequency dependence of the phase velocity (dispersion relation). Broadband or variable-frequency, quasi-plane wave SAWs are generated by a line-focused, 200-ps pulsed laser. The out-of-plane SAW displacement amplitudes are measured using a path-stablized Michelson interferometer with line-focus detection. The apparatus incorporates differential photodiode detection with a −3-dB bandwidth of 40 kHz–800 MHz. With this system, several displacement waveforms over a range of propagation distances are acquired and used to determine the SAW dispersion. Dispersion relations up to 200 MHz are presented for a variety of specimens, including a series of Si wafers with TiN films 0.2–1.3 micrometers thick and containing residual stress. The results illustrate the applicability of this technique to various conditions such as stiffening and loading films and isotropic and anisotropic substrates. The experimental dispersion curves obtained with this method are compared to theoretical predictions to evaluate the film elastic properties.

A vibrating optical fiber tip as a new sensor to monitor organic vapors

A novel transducer concept using a vibrating fiber tip for sensing vapors of organic compounds is outlined. It is based on a vibrating optical glass fiber, which is excited via a dither piezo tube (DPT), whereby changes of the vibration of the fiber tip are monitored using position-sensitive detection (PSD). The latter consists of a light source in the form of an appropriate laser diode, the emission of which is coupled into the vibrating fiber, and a matching differential photodiode as the detector. The influence of both polar and non-polar organic vapors on the vibrating fiber tip has been investigated. Our measurements show that the vibration even of a bare fiber tip (e.g. of a glass fiber without any coating of an active layer) is affected by the presence of polar organic vapors, apparently by their influence on the elastic behavior of the fiber. This sensor reaction is influenced by the surface properties of the fiber, because fibers with HMDS-treated surfaces or fibers coated with active layers react intrinsically different from bare fibers.

Three-Dimensional Motion of the Organ of Corti

The vibration of the organ of Corti, a three-dimensional micromechanical structure that incorporates the sensory cells of the hearing organ, was measured in three mutually orthogonal directions. This was achieved by coupling the light of a laser Doppler vibrometer into the side arm of an epifluorescence microscope to measure velocity along the optical axis of the microscope, called the transversal direction. Displacements were measured in the plane orthogonal to the transverse direction with a differential photodiode mounted on the microscope in the focal plane. Vibration responses were measured in the fourth turn of a temporal-bone preparation of the guinea-pig cochlea. Responses were corrected for a “fast” wave component caused by the presence of the hole in the cochlear wall, made to view the structures. The frequency responses of the basilar membrane and the reticular lamina were similar, with little phase differences between the vibration components. Their motion was rectilinear and vertical to the surface of their membranes. The organ of Corti rotated about a point near the edge of the inner limbus. A second vibration mode was detected in the motion of the tectorial membrane. This vibration mode was directed parallel to the reticular lamina and became apparent for frequencies above ∼0.5 oct below the characteristic frequency. This radial vibration mode presumably controls the shearing action of the hair bundles of the outer hair cells.

A force transducer for measuring mechanical properties of single cardiac myocytes

We have described a transducer design capable of recording forces generated by single cardiac myocytes with sufficient temporal resolution to detect force responses to rapid length changes. Our force sensors were made from thin steel foils that act as cantilevers whose bending is monitored by reflection off a laser beam. Deflection of the laser beam is measured by a differential photodiode detector. A small, 50-micron-thick tungsten needle attached to the free end of the steel foil allowed us to glue single cardiac cells to the force transducer. The transducers have compliances of approximately 0.02 m/N and resonance frequencies between 2 and 3 kHz. The resolution is approximately 18 nN rms at a detector bandwidth of 16 kHz, so we were able to resolve 0.2% of the maximum isometric force ( approximately 12 microN) developed by a single cardiac myocyte. We have demonstrated that the transducer is well suited to analysis of mechanical properties of single ventricular myocytes, for example, the recording of isometric forces and rate constants of force redevelopment after rapid release-restretch maneuvers.

Reduced-noise-displacement measurements with a correlated differential photodiode sensor

A measured displacement resolution of <3 nm is demonstrated with a common cathode differential photodetector combined with a laser-diode optical source and a fiber-optic collimator. Resolution, standard deviation, and differences between maxima and minima values for the residuals of the least-squares fit suggest that a coherent laser-diode source temporally correlates photoelectron flux between adjacent detector segments, suggesting reduced signal variance and associated electronic (shot) noise. For otherwise similar systems, the laser-diode source provides approximately an order of magnitude reduction in standard deviation compared with a light-emitting-diode source, which implies an equivalently improved measured (including standard deviation) resolution. Combined variances for correlated and uncorrelated detectors and their measured variances are outlined. The measured resolution is a sum of both the (ideal) mathematical variance based on the detector noise (millivolts) divided by the system sensitivity (millivolts per nanometer, and the standard deviation of the noise (nanometers).

Mechanical and electromechanical properties of the stereovillar bundles of isolated and cultured hair cells of the chicken

Isolated single chicken hair cells and pieces of epithelium without the tectorial membrane, either freshly isolated or in tissue culture, were studied using water-jet stimulation of their stereovillar bundles and current injection. Responses were measured under enhanced video-microscopic observation or while using a differential photodiode technique sensitive down into the nanometer range. When stimulated with a water jet at low displacement amplitudes up to about 200 nm, the stereovillar bundle displacement was asymmetrical, indicating a lower stiffness in the excitatory direction, but the reverse was true at higher displacement amplitudes. Undamaged bundles showed no mechanical resonances below 1 kHz. In damaged bundles, however, such resonances were prominent and accompanied by splaying of the stereovilli. Hair cells in the epithelium showed small bundle movements (0.6 nm/mV) whose polarity depended on the polarity of the injected current. These movements probably resulted from activation of the bundle's adaptation motors.

Reversible inhibition of voltage-dependent outer hair cell motility and capacitance

Outer hair cells (OHC) from the organ of Corti are capable of fast voltage-induced length changes (Santos-Sacchi and Dilger, 1988), suggesting that an associated voltage sensor should reside in the OHC plasma membrane. Voltage-dependent mechanical responses and nonlinear charge movement of isolated OHCs from the guinea pig were analyzed using the whole-cell voltage-clamp technique. Ionic currents in the cells were blocked. Nonlinear voltage-dependent charge movement or, correspondingly, voltage-dependent capacitance was measured with step or AC analysis. OHC movements were measured either from video or using a differential photodiode technique. Maximum charge movements up to 2.5 pC were measured in OHCs from the low-frequency region of the cochlea. Both AC and step analyses indicated a peak nonlinear capacitance of 16-17 pF. The voltage dependence was fit to a Boltzmann relation with the step analysis indicating a maximum nonlinear capacitance at -23 mV step potential from a holding potential of about -120 mV, and AC analysis indicating a maximum at a holding potential near -40 mV. AC analysis probably provides a more accurate evaluation of voltage dependence. Measures of OHC motility magnitude versus voltage follow the nonlinear capacitance-voltage function obtained from AC measures. Treatment of the cells with gadolinium ions (0.5-1 mM) blocked OHC motility. This treatment also produced a shift of the nonlinear capacitance function along the voltage axis in the depolarizing direction, which can be explained by membrane surface charge screening. However, maximum capacitance was reduced as well and may correspond to the reduction or abolition of OHC motility in response to gadolinium treatment. Gadolinium effects were reversible. Nonlinear capacitance is not a function of membrane deformation due to length changes, since removal of OHC cytosol via the patch pipette abolished longitudinal movement but did not reduce nonlinear charge movement. It is interesting to note that the nonlinear capacitance will dynamically influence the time constant of the OHC during acoustically evoked receptor potential generation.

An automatically capillary viscometer with accuracy of one part in 5×106

An automatic Ubbelohde type viscometer with accuracy of 0.1 p.p.m. was developed. It was shown that using a differential photodiode, flow-times of the order of 1000 s could be measured with an accuracy of +or-100 mu s. A description of the viscometer and time measuring system is given.