Carrier Leak Research Articles

Infliximab after Boston Keratoprosthesis in Stevens–Johnson Syndrome: An Update

ABSTRACTPurpose: To report our experience using intravenous infliximab for the treatment of tissue melt after Boston keratoprosthesis (B-KPro) types I and II in patients with autoimmune disease.Methods: Case series.Results: We identified four patients who were treated with intravenous infliximab in the context of tissue melt after B-KPro. Stevens–Johnson syndrome-associated corneal blindness was the primary surgical indication for B-KPro implantation in all patients. Two patients received a B-KPro type I and two patients received a B-KPro type II. The patients received intravenous infliximab for skin retraction around B-KPro type II, melting of the carrier graft or leak. Treatment resulted in a dramatic decrease in inflammation and, in some cases, arrest of the melting process. Cost and patient adherence were limiting factors to pursuing infliximab therapy. In addition, one patient developed infusion reactions.Conclusions: Intravenous infliximab may be considered as globe- and sight-saving therapy for tissue melt after B-KPro.

Size Quantization Effects on Interfacial Electron Transfer Dynamics in Ru(II)–Polypyridyl Complex Sensitized ZnO QDs

Quantum-size confinement in semiconductor material offers size based tunability of interband gap energy as well as intraband sublevels. In this work, size quantization of wide bandgap ZnO quantum dots has been explored in the study of interfacial charge separation reaction using a catechol functionalized Ru(II)–polypyridyl complex as a photosensitizer molecule. Femtosecond time-resolved transient absorption studies have revealed multiple electron injection events based on discrete conduction band states of ZnO QDs. The electron injection rates have been rationalized for quantum confinement effects owing to different sizes of ZnO QDs. Furthermore, the size dependency of the intrinsic lifetime of electrons injected into discrete energy levels of ZnO QDs has been revealed in charge recombination reaction with the Ru(III)–polypyridyl complex cation. The charge recombination dynamics reveals a competing trend of carrier confinement and carrier leak upon reducing particle size. This study shows the optimization of finite size effects in achieving better interfacial charge separation at the dye/semiconductor interface.

A 26 GHz Transceiver Chipset for Short Range Radar Using Post-Passivation Interconnection

We demonstrate a 26 GHz SiGe bipolar complementary metal oxide semiconductor (BiCMOS) transceiver chipset for short-range spread-spectrum (SS) radar system. The integrated frequency triplers lower the local oscillation frequency down to 8.8 GHz, and eliminate the carrier leak in the transmitting signal which enables high sensitivity. The on-chip balun connected to the mixer demodulating by the pseudo noise (PN) code in the receiver increases the dynamic range of the receiving signal. Low-loss transmission lines on Si substrate are fabricated by post-passivation interconnection process using thick benzocyclobutene (BCB). We have confirmed the transmitting signal having spread-spectrum with suppressing the carrier leak, the improvement of the dynamic range of the receiver, and the reduction of the transmission loss on Si substrate. We have demonstrated the operation of the 26 GHz ultra wide band (UWB) SS radar, corresponding to detecting a human located at 7 m away from the system.

Residual-carrier-free burst oscillator for automotive UWB radar applications

The design and performance of an MMIC burst oscillator that oscillates only while the driving pulse is applied are described. Since it does not generate carrier leak, a UWB radar using this oscillator may effectively mitigate interference with services using the restricted frequency band by locating its spectrum sufficiently far from the band.

A CMOS Oversampling Bandpass Cascaded D/A Converter With Digital FIR and Current-Mode Semi-Digital Filtering

An oversampling bandpass digital-to-analog converter has been designed so as to eliminate the carrier leak and in-band SNR degradation that accompany I and Q channel mismatch in wireless transmitters. The converter combines a cascaded noise-shaping sigma-delta (/spl Sigma//spl Delta/) modulator with digital finite impulse response (FIR) and mixed-signal semi-digital filters that attenuate out-of-band quantization noise. The performance of the converter in the presence of current source mismatch has been improved through the use of bandpass data weighted averaging. An experimental prototype of the converter, integrated in a 0.25-/spl mu/m CMOS technology, provides 83 dB of dynamic range for a 6.25-MHz signal band centered at 50 MHz, and suppresses out-of-band quantization noise by 38 dB.

A new radio receiver system for personal communications

A new radio receiver system for personal communications is described. This technology incorporates direct conversion into an integrated circuit in such a way that the need for discrete IF filters is avoided. It also employs a second IF functional circuit that contains a carrier leak detector and an adjustment-free system. The carrier leak detector suppresses the level of unwanted carrier leak and the adjustment-free system automatically compensates for any variation in circuit response that corrupts the performance of the receiver. The resulting design is particularly suitable for use in wireless devices such as pagers and cordless telephones. >

Spectral sensitivity of power amplifiers to quadrature modulator misalignment

Misalignments in the quadrature modulator feeding a nonlinear high power amplifier can produce distortion products that lead to spectrum leakage into adjacent channels. Expressions are derived relating the out-of-band spectra to these misalignments and to the complex coefficients of the power series describing the amplifier. For most applications the adjacent channel leakage is proportional to the square of the misalignment error (carrier leak, differential gain, differential phase and level error) except in the case of some higher order products of continuous phase modulations (CPM). A technique for estimating the spectrum for the above situations is described. It involves summing the weighted spectrum of each distortion product. The weighting coefficients can be varied to account for amplifier characteristics, backoff, and misalignment error. The analysis is applicable to linear or continuous phase modulations with or without predistortion. The spectrum estimate is particularly good for continuous phase modulated signals where the error is normally much less than 1 dB.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Correction of mixer nonlinearity in quadrature modulators

Baseband preconditioning is used to partially cancel third order nonlinearities in mixers. Calibration is by means of a simple diode detector, but requires the presence of a carrier leak signal. The technique led to an improvement of 8dB in IM3 for a 900 MHz system.

Automatic adjustment of quadrature modulators

A technique for the automatic correction of errors in RF quadrature modulators is described. The method uses a diode detector to provide amplitude feedback to guide the adaption of baseband circuits that correct for carrier leak, differential gain and phase mismatch errors.

A modified N-path filter suited for practical realization

A method is presented which makes it possible to build filters that, in some respect, behave like N -path filters but without suffering from the well-known disadvantages associated with the implementation of these latter filters, namely, incomplete cancellation of unwanted sidebands and interference caused by carrier leakage. In conventional N -path filters the output signal is formed by summing signals which have been processed by N distinct paths, each path containing an intermediate network between input and output modulators. The method to be presented consists in using one single path completely in time division multiplex. This way the generation of interfering sidebands is avoided and carrier leak occurs at frequencies where it causes no trouble. A general output-to-input relationship is derived for the ideal case, and the result is given as a time-varying system function. With the aid of an example the effect of nonideal behavior which is encountered with practical circuits is analyzed. Some practical results are shown.

Feedback method for suppressing carrier leak

A feedback method for suppressing carrier leak (and any carrier-frequency output component due to a d.c. offset at the input) in balanced modulators and multipliers is described which promises to be particularly effective when used in quadrature modulation systems. The method is basically simple, but a search of the literature has failed to uncover any reference to a similar scheme.

Narrow-bandpass filtering with modulation

To overcome the problems of carrier leak etc. experienced with N-path filters incorporating active lowpass filters, it has been suggested that N-path filters incorporating bandpass filters (which must be well matched) be used to produce a pair of passbands away from the carrier frequency, with another filter at the required final frequency to discriminate between the wanted and the image passbands. An alternative and practical solution is described here in which neither the well matched low-frequency filters nor the additional high-frequency filter are required; instead a single low-frequency bandpass filter and two pairs of elementary phase-shift networks are used. The circuit is well suited to realisation as a thin-film or hybrid integrated circuit, since all the frequency-selective circuits operate at the low frequency.

Optoelectronic amplitude modulators

An optoelectronic amplitude modulator is described, which uses a GaAs diode as a carrier source and a PbS photoconductor as the modulation element. Wide dynamic range, negligible carrier leak and a poor frequency response are features.

Balanced modulators with stable low carrier leak

Balanced modulators with stable low carrier leak

Carrier-voltage control for improved dynamic range in rectifier modulators

A technique for increasing the dynamic range of a balanced modulator by automatic adjustment of the carrier amplitude is described. A peak detector is used to sense the amplitude of input signals, and to control a variable-gain amplifier which reduces the carrier amplitude—and hence the carrier leak—for small inputs. It is shown that some commercially available modulator diodes are satisfactory for use in the system, although ideally bilinear diodes are required. Some experimental results on a phase-sensitive detector are included.

The sources of error in Hall-effect multipliers

The errors produced in a Hall-effect multiplier are examined and shown to belong to one of two categories: either they are due to coupling between input or output, or they are produced by non-linear processes within the device. An estimate of the magnitude of the errors is given and interpreted in terms of carrier leak, modulation leak and envelope distortion for the particular application of a Hall-effect modulator. A comparison is made between plates constructed of indium antimonide and indium arsenide on the bases of carrier suppression, temperature stability, conversion efficiency and distortion. Carrier suppressions of up to 80 dB can be obtained for both materials.

A rectifier modulator with stable low carrier-leak

The paper is concerned with the development of a modulator capable of giving much lower stable levels of carrier leak than previously obtained. After consideration of various types of modulator, the conclusion is reached that the constant-current modulator, originally proposed by Cooper, is probably capable of giving the highest stable level of carrier rejection. This modulator consists, essentially, of a ring modulator whose input transformer is, ideally, replaced by infinite-impedance valve generators feeding each rectifier input terminal. The action of the constant-current modulator is analysed in detail on the basis of small differences in the characteristics of the rectifying elements, and associated topics are discussed. Experimental evidence, obtained using a carrier frequency of 3 kc/s, is given which, to a considerable degree, supports the theoretical analysis. The modulator, thus developed, is capable of giving carrier leak levels more than 90 dB below the carrier current from each source which are stable with temperature and time. Also, the action of the modulator is such that the fundamental component of the carrier leak is not affected by relatively large unbalances in the carrier currents from each source.

Carrier-leak in rectifier modulators of the shunt type

An experimental study has been undertaken in an endeavour to achieve an understanding of the mechanism of carrier-leak in shunt modulators, to elucidate some of the factors affecting the attainment of low leak levels (in the range 40 to 80 dB below the carrier voltage), and to investigate the possibilities of d.c. balancing of the rectifier bridge.With a square-wave carrier voltage in a non-reactive circuit (or at low frequencies) conditions approximate to those of ideal switching; carrier-leak is a function of the unbalance of the rectifier resistances for two specific voltages (one positive and one negative) and is quite calculable. A very low total leak voltage (i.e. including all frequency components) can be obtained by means of a simple resistance balance. The correlation of d.c. and a.c. components of the leak is excellent if rectifiers with high or alternatively well-balanced back-resistances are used.With a sinusoidal carrier supply, carrier-leak arises during the transition period of rectifier switching (i.e. during the change from forward to backward resistance and vice versa), and can therefore no longer be completely eliminated by a simple resistance control. Complete suppression of any one component (usually the fundamental) is theoretically possible in the non-reactive case, but in practice, unbalance of rectifier and stray reactances gives rise to a finite leak voltage. Results, even at low frequencies (less than 5 kc/s), are thus inferior to those obtained using a square-wave carrier, and in the experimental circuit it was difficult to obtain, by resistance balancing, fundamental components of the leak voltages lower than 0.1% of the carrier forward peak potential difference. Correlation between d.c. and a.c. balance conditions is also inferior, and zero d.c. leak might correspond to anything up to 0.4% leak of fundamental a.c. component. It is shown that the use of a capacitive as well as a resistive balance control can reduce leak voltages to a very low order, approaching—and with care equalling—zero on a short-term basis.At higher frequencies, reactance unbalance plays a very large part in the production of carrier leak. It is demonstrated that the minimum fundamental leak voltage obtainable with a resistive balance alone rises linearly as frequency is increased, and that a combination of resistive and reactive balance controls can be used to achieve suppression of one component as good as, or better than, that obtained at low frequencies without a reactive balance.The a.c./d.c. correlation at high frequencies is quite reasonable, even with a reactive unbalance. With an unbalance of 50 μμF at 1 kc/s (equivalent to the probable value of 0.5ppμμF at 100kc/s) correlation was such that for zero d.c. leak the a.c. fundamental leak did not exceed about 0.5% of the carrier forward peak potential difference.It appears to be a fairly safe general conclusion that control of carrier-leak adjustment by the use of a d.c. meter is likely to prove very useful in practice and, provided that efficient rectifiers are used, should enable a.c. leak voltages to be maintained at least 40 dB below the carrier voltage across the rectifiers.Under reactive conditions, the effect of carrier-generator impedance is complicated. If it is itself partly reactive, the capacitance balance becomes frequency dependent, i.e. a different adjustment of the balancing capacitor is required at each frequency. This dependence on the carrier-generator impedance is probably due to the fact that the rectifier bridge is not truly balanced over the whole switching cycle, but is merely adjusted to give a minimum output of one particular frequency.Some results are given for the type of shunt modulator having no transformer—a useful alternative to the Cowan type. Very low leak voltages are shown to be obtainable by adjustment of the relative value of the two coupling capacitors.

Some aspects of the design of balanced rectifier modulators for precision applications

The design of balanced rectifier modulators of ring and Cowan types is discussed, and it is shown how the performance of the modulator depends on rectifier characteristics, the circuit impedance in which the modulator operates, the resistance of the carrier generator and the carrier voltage.The main performance features discussed are efficiency, stability, production of unwanted modulation products, impedance, and carrier leak.It is shown that there are advantages in designing a modulator for maximum efficiency by choosing a circuit impedance of optimum value and a carrier supply of high resistance. Variations in efficiency due to variations in carrier voltage, circuit impedance and temperature are then a minimum although it may be necessary to have each rectifier shunted with a constant resistance to achieve this. The production of modulation products of higher order is greatest in a modulator of maximum efficiency in which the circuit providing the carrier is of high resistance, and is reduced considerably if inefficient working and a low-resistance circuit are used. Further reduction, if desired, can be obtained by the use of a large bias on the rectifiers, and it has been found possible to reduce the 3fc±f sidebands to over 26 db below the fc + f sidebands (where fc = carrier frequency and f = signal frequency). This method is of value only in ring modulators, as with the Cowan circuit it introduces products of the type 2fc + f.It is shown that the ordinary potentiometer adjustment for carrier leak compensates only the unbalances between the low forward resistances of the rectifiers, and there remains an out-of-balance current at small values of the instantaneous carrier voltage. This effect can be reduced by using a high-resistance carrier supply and by appropriate selection of the rectifiers; a further improvement, in the case of ring modulators, can be obtained by the use of large biases on the rectifiers. Carrier leaks as low as − 60 db relative to 1 volt in 600 ohms, or 40 db below sideband-level, when high-level signals are applied, can readily be obtained and maintained in modulators with at least 1 volt carrier peak voltage across the rectifiers.It is assumed throughout that the rectifiers are purely resistive, as with the diodes and crystal valves now available, the effect of the capacitance is negligible up to frequencies of the order of 1 Mc/s.A method of design of a ring modulator is described in which the input impedance remains relatively constant over the cycle of carrier voltage; this may have important applications in precision circuits.