Commercial Amplifier Research Articles

Laser-produced plasma-based extreme-ultraviolet light source technology for high-volume manufacturing extreme-ultraviolet lithography

Since 2002, we have been developing a CO2-Sn-laser plasma produced (LPP) extreme-ultraviolet (EUV) light source, the most promising solution as the 13.5-nm high-power (>200 W) light source for high-volume manufacturing (HVM) EUV lithography. Because of its high efficiency, power scalability, and spatial freedom around plasma, we believe that the CO2-Sn-LPP scheme is the most feasible candidate as the light source for EUVL. By now, our group has proposed several unique original technologies, such as CO2 laser-driven Sn plasma generation, double-laser pulse shooting for higher Sn ionization rate and higher CE, Sn debris mitigation with a magnetic field, and a hybrid CO2 laser system that is a combination of a short-pulse oscillator and commercial cw-CO2 amplifiers. The theoretical and experimental data have clearly demonstrated the advantage of combining a laser beam at a wavelength of the CO2 laser system with Sn plasma to achieve high CE from driver laser pulse energy to EUV in-band energy. We have the engineering data from our test tools, which include 20-W average clean power, CE = 2.5%, and 7 h of operating time; the maximum of 3.8% CE with a 20-μm droplet, 93% Sn ionization rate, and 98% Sn debris mitigation by a magnetic field. Based on these data, we are developing our first light source for HVM: GL200E. The latest data and the overview of EUV light source for the HVM EUVL are reviewed in this paper.

Affine Projection 알고리즘에 기초하여 구현한 디지털 전치왜곡을 이용한 RF 전력증폭기의 선형성 향상

In this paper, we design a digitally pre-distorted RF power amplifier operating in 900 MHz band. The linearity of RF power amplifier is improved by employing the digital pre-distortion(DPD) based on affine projection(AP) algorithm, where the look-up table(LUT) method is used with non-linear indexing. The proposed DPD with AP algorithm is compared with that with normalized least mean square(NLMS) algorithm, applied to the RF power amplifier. A commercial power amplifier module is used for verification of the proposed algorithm which shows improvement of adjacent channel leakage ratio(ACLR) by about 21 dB.

Recording evoked potentials during deep brain stimulation: development and validation of instrumentation to suppress the stimulus artefact

The clinical efficacy of deep brain stimulation (DBS) for the treatment of movement disorders depends on the identification of appropriate stimulation parameters. Since the mechanisms of action of DBS remain unclear, programming sessions can be time consuming, costly and result in sub-optimal outcomes. Measurement of electrically evoked compound action potentials (ECAPs) during DBS, generated by activated neurons in the vicinity of the stimulating electrode, could offer insight into the type and spatial extent of neural element activation and provide a potential feedback signal for the rational selection of stimulation parameters and closed-loop DBS. However, recording ECAPs presents a significant technical challenge due to the large stimulus artefact, which can saturate recording amplifiers and distort short latency ECAP signals. We developed DBS-ECAP recording instrumentation combining commercial amplifiers and circuit elements in a serial configuration to reduce the stimulus artefact and enable high fidelity recording. We used an electrical circuit equivalent model of the instrumentation to understand better the sources of the stimulus artefact and the mechanisms of artefact reduction by the circuit elements. In vitro testing validated the capability of the instrumentation to suppress the stimulus artefact and increase gain by a factor of 1000 to 5000 compared to a conventional biopotential amplifier. The distortion of mock ECAP (mECAP) signals was measured across stimulation parameters, and the instrumentation enabled high fidelity recording of mECAPs with latencies of only 0.5 ms for DBS pulse widths of 50 to 100 µs/phase. Subsequently, the instrumentation was used to record in vivo ECAPs, without contamination by the stimulus artefact, during thalamic DBS in an anesthetized cat. The characteristics of the physiological ECAP were dependent on stimulation parameters. The novel instrumentation enables high fidelity ECAP recording and advances the potential use of the ECAP as a feedback signal for the tuning of DBS parameters.

Wideband linear power amplifier for high-frequency ultrasonic coded excitation imaging

Linear power amplifiers are critical components in ultrasonic imaging systems that implement chirp-coded excitation. Bench-top commercial power amplifiers are usually used in academic laboratories for high-frequency ultrasound imaging, and the imaging performance depends greatly on these general-purpose instruments. To achieve a wide dynamic range, a power amplifier consisting of two stages is developed for chirp-coded ultrasound imaging applications through the implementation of custom-designed broadband 1:1 transformers and the optimization of feedback circuits. The amplifier has broad bandwidth (5 to 135 MHz), maintaining a linearity up to the 1-dB gain compression point (P1dB) of 41.5 dBm, allowing 16 dBm input power level at 60 MHz. The mean and the maximum values of output third-order intercept points (OIP3) are 51.8 and 53.5 dBm, respectively, between 20 and 110 MHz. With 12 dBm input power, the gain of the amplifier varies between 24 and 29 dB, offering a uniformity which would allow excitation of a 70-MHz single-element transducer with windowed chirp-coded bursts sweeping from 40 to 100 MHz. The performance in high-frequency ultrasound imaging is evaluated with a wire phantom. Echo signal-to-noise ratio (eSNR) of the designed amplifier is 7 dB better than a commercial amplifier, and spatial resolution is maintained.

Broadband Chromium-Doped Fiber Amplifiers for Next-Generation Optical Communication Systems

We report the first experimental breakthrough of a net gain of optical signals in a broadband chromium-doped fiber amplifier (CDFA) for next-generation optical communication systems. Current fiber amplifiers, including commercial erbium-doped fiber amplifier, cover only a relatively small portion of the entire transmission bandwidths (1300-1600 nm) of the low-loss windows of silica fibers. The newly developed CDFAs have opened up the possibility of utilizing the 300-nm entire spectrum of the low-loss fibers to further increase the transmission capacity. In this paper, we present the experimental demonstration of a net gain of 1.2 dB employing gain enhancement technique. With the help of an optical-fiber system examination for the CDFA, a 40-Gb/s error-floor free data transmission was successfully demonstrated by realizing the high-speed transmission of signal with gain through the chromium-doped fibers (CDFs). Further gain improvement in the CDFAs employing few-mode or single-mode CDFs will be presented and discussed.

40-Gb/s NRZ-to-RZ and OOK-to-BPSK Format and Wavelength Conversion on a Single SOA-MZI for Gridless Networking Operations

We propose and experimentally demonstrate simultaneous format and wavelength conversion at 40 Gb/s exploiting a single commercial semiconductor optical amplifier Mach-Zehnder interferometer. Conversion from nonreturn-to-zero (NRZ) to a 2-ps return-to-zero (RZ) on-off keying (OOK) format suitable for grooming onto a 160-Gb/s optical time-division-multiplexing frame is achieved. Furthermore, for the first time to the best of our knowledge, 40-Gb/s conversion from RZ OOK to RZ binary phase-shift keying (BPSK) is achieved. The effectiveness of the proposed scheme is demonstrated by means of bit-error-rate measurements. Error-free operations are reported, with a power penalty of 0.5 dB for the case of NRZ-to-RZ OOK conversion and of 3 dB (comprehensive of the degradation due to the wavelength conversion used to generate the probe signal) for the case of OOK-to-BPSK conversion.

다중 대역 전송 시스템을 위한 전치왜곡 알고리즘

New digital predistortion technique is proposed for power amplifier linearization in multi-band transmission systems. We consider a system where muli-band signals are combined and amplified by a single power amplifier (PA). In this system, the PA output is distorted by the nonlinear cross-products between different band signals as well as their own nonlinear self-products. To compensate these nonlinear effects, we propose a multiple PD structure. Each PD removes the nonlinear cross-products and self-products to mitigate the spectral regrowth for the corresponding band. Since the PD parameters for different bands are linked together, it is difficult to find the PD parameters separately. Thus, we propose an iterative method for finding the PD parameters jointly. For demonstration of the proposed method, multi-band characteristics of PA are extracted from a commercial power amplifier. Computer simulation was executed based on the PA parameters. The simulation results show that the proposed method can effectively linearize the PA and remove spectral regrowth at each signal band.

Examination of Measurement Method for Magnetostriction of Electrical Steel Sheet with Lock-in Amplifier

It is important to measure magnetostriction under mechanical stress in order to clarify the relationships between magnetic property and stress. However, it is difficult to measure the magnetostriction of the electrical steel sheet because the quantity of the magnetostriction is very small. In this paper, we examine measurement method with a lock-in amplifier to improve the measurement accuracy of magnetostriction. From the result, the lock-in amplifier is very useful to measure the magnetostriction of the electrical steel sheet in comparison with a commercial strain amplifier.

LINEARIZATION OF RF POWER AMPLIFIERS USING ADAPTIVE KALMAN FILTERING ALGORITHM

In this paper, a new linearization algorithm of power amplifier (PA), based on Kalman filtering theory is proposed for obtaining fast convergence of the adaptive digital predistortion. The proposed method uses the real-time digital processing of baseband signals to compensate the nonlinearities and memory effects in radio-frequency power amplifier. To reduce the complexity of computing in classical Kalman filtering, a sliding time-window has been inserted which combines offline measurement and online parameter estimation with high sampling time to track the changes in the PA characteristics. The performance of the proposed linearization scheme is evaluated through simulation and experiments. Using digital signal processing, experimental results with commercial power amplifier are presented for multicarrier signals to demonstrate the effectiveness of this new approach.

An equivalent circuit-based approach to behavioral modeling of long-term memory effects in wideband amplifiers

A behavioral model for power amplifiers that accounts for long-term memory effects is proposed in this article.The model structure is derived from a simplified circuit level description of thermal power feedback and a dynamic ordering of model kernels. The approach has been tested with commercial class-A and class-AB power amplifiers, showing an excellent accuracy in the description of nonlinear distortion associated with low-frequency memory effects. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2278–2281, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26239

Current feedback operational amplifiers as fast charge sensitive preamplifiers for photomultiplier read out

Fast charge sensitive preamplifiers were built using commercial current feedback operational amplifiers for fast read out of charge pulses from a photomultiplier tube. Current feedback opamps prove to be particularly well suited for this application where the charge from the detector is large, of the order of one million electrons, and high timing resolution is required. A proper circuit arrangement allows very fast signals, with rise times down to one nanosecond, while keeping the amplifier stable. After a review of current feedback circuit topology and stability constraints, we provide a "recipe" to build stable and very fast charge sensitive preamplifiers from any current feedback opamp by adding just a few external components. The noise performance of the circuit topology has been evaluated and is reported in terms of equivalent noise charge.

비선형 인덱싱 함수 Tanh로 구현한 디지털 전치 왜곡을 이용한 RF 전력증폭기의 선형성 향상

In this paper, we design a digital predistortion(DPD) for linearity enhancement of RF power amplifier operating in 900 MHz band. We verify improvement of linearity by comparing the proposed DPD using tanh as a nonlinear indexing function and the DPD using linear indexing function based on signal amplitude. The digital predistortion is realized by look-up table(LUT) method, and the Saleh model is employed for power amplifier modeling, then a commercial power amplifier module is used for measurement. The LUT has 256 tables, and the NLMS(Normalized Least Mean Square) algorithm was utilized for an adaptive algorithm for estimation. As a result, we improve the ACLR(Adjacent Channel Leakage Ratio) by around 15 dB.

Generation of broadly tunable sub-30-fs infrared pulses by four-wave optical parametric amplification

We report on the generation of sub-30-fs near-IR light pulses by means of broadband four-wave parametric amplification in fused silica. This is achieved by frequency downconversion of visible broadband pulses provided by a commercial blue-pumped beta-barium borate crystal-based noncollinear optical parametric amplifier. The proposed method produces the IR idler pulses with energy up to ∼20 μJ and tunable in wavelength from 1 to 1.5 μm. The shortest pulse duration is 17.6 fs, measured at 1.2 μm.

Type-I cascaded quadratic soliton compression in lithium niobate: Compressing femtosecond pulses from high-power fiber lasers

The output pulses of a commercial high-power femtosecond fiber laser or amplifier are typically around 300-500 fs with a wavelength around 1030 nm and 10s of $\mu$J pulse energy. Here we present a numerical study of cascaded quadratic soliton compression of such pulses in LiNbO$_3$ using a type I phase matching configuration. We find that because of competing cubic material nonlinearities compression can only occur in the nonstationary regime, where group-velocity mismatch induced Raman-like nonlocal effects prevent compression to below 100 fs. However, the strong group velocity dispersion implies that the pulses can achieve moderate compression to sub-130 fs duration in available crystal lengths. Most of the pulse energy is conserved because the compression is moderate. The effects of diffraction and spatial walk-off is addressed, and in particular the latter could become an issue when compressing in such long crystals (around 10 cm long). We finally show that the second harmonic contains a short pulse locked to the pump and a long multi-ps red-shifted detrimental component. The latter is caused by the nonlocal effects in the nonstationary regime, but because it is strongly red-shifted to a position that can be predicted, we show that it can be removed using a bandpass filter, leaving a sub-100 fs visible component at $\lambda=515$ nm with excellent pulse quality.

Implementation and evaluation of simultaneous video-electroencephalography and functional magnetic resonance imaging

The objective of this study was to demonstrate that the addition of simultaneous and synchronised video to electroencephalography (EEG)-correlated functional magnetic resonance imaging (fMRI) could increase recorded information without data quality reduction. We investigated the effect of placing EEG, video equipment and their required power supplies inside the scanner room, on EEG, video and MRI data quality, and evaluated video-EEG-fMRI by modelling a hand motor task. Gradient-echo, echo-planner images (EPI) were acquired on a 3-T MRI scanner at variable camera positions in a test object [with and without radiofrequency (RF) excitation], and human subjects. EEG was recorded using a commercial MR-compatible 64-channel cap and amplifiers. Video recording was performed using a two-camera custom-made system with EEG synchronization. An in-house script was used to calculate signal to fluctuation noise ratio (SFNR) from EPI in test object with variable camera positions and in human subjects with and without concurrent video recording. Five subjects were investigated with video-EEG-fMRI while performing hand motor task. The fMRI time series data was analysed using statistical parametric mapping, by building block design general linear models which were paradigm prescribed and video based. Introduction of the cameras did not alter the SFNR significantly, nor did it show any signs of spike noise during RF off conditions. Video and EEG quality also did not show any significant artefact. The Statistical Parametric Mapping{T} maps from video based design revealed additional blood oxygen level-dependent responses in the expected locations for non-compliant subjects compared to the paradigm prescribed design. We conclude that video-EEG-fMRI set up can be implemented without affecting the data quality significantly and may provide valuable information on behaviour to enhance the analysis of fMRI data.

Comparison in Power Consumption of Synchronous and Asynchronous Optical Packet Switches

Power consumption is expected to become the main limiting factor for scaling the current network architectures to capabilities of hundreds of terabit or even petabits. The use of optical switching fabrics (SFs) could relax the limitations to some extent but large optical buffers occupy larger area and dissipate more power than electronic ones. In this paper, we evaluate the power consumption of bufferless optical packet switches (OPSs), using the wavelength conversion to solve the output packet contentions. Sophisticated analytical models are introduced to evaluate the power consumption of synchronous and asynchronous OPSs (SOPSs and AOPSs) versus the offered traffic, the main switch parameters, and the used device characteristics. The power consumption in SOPSs and AOPSs is compared when commercial semiconductor optical amplifiers are used to implement SFs and wavelength converters (WCs). The obtained results show that the high power consumption in synchronization stage makes SOPS less effective than AOPS in terms of power consumption. For instance, when the OPSs are dimensioned with a sufficient number of WCs and offered traffic is 0.8, SOPS consumes 140% of power more than does the AOPS. Finally, though power consumption due to cooling system is not considered in the proposed model, we observe that both SOPSs and AOPSs consume much less power per gigabit per second carried than commercial routers.

On the Stability of Shield-Driver Circuits

This paper analyzes the stability of shield-driver circuits (SDCs) applied to the measurement of remote signal sources (such as bioelectric signals) and then proposes design ideas to guarantee it. According to the performed analysis, there are at least two factors that explain the potential instability of the SDC: 1) a high order of the SDC transfer function and 2) the parasitic inductance of the interconnecting cable. The former makes the circuit unstable for intermediate values of the output resistance <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RS</i> of the signal source, whereas the latter makes the circuit unstable for low values of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RS</i> . These theoretical predictions are experimentally validated using several commercial operational amplifiers.

Calibration of Field II using a convex ultrasound transducer

Field II is an ultrasound simulation program capable of simulating the pressure scattering from inhomogeneous tissue. The simulations are based on a convolution between spatial impulse responses from the field in front of the transducer and the volt-to-surface acceleration impulse response of the transducer. For such simulations to reflect actual measured intensities and pressure levels, the transducer impulse response is to be known. This work presents results of combining a modified form of a 1D linear transducer model originally suggested by Willatzen together with the Field II program to calibrate the pressure and intensity simulations of a 128 element convex medical transducer with elevation focus at 70 mm. The simulations are compared to pressure measurements from a transducer driven at 4.0 MHz using a research scanner with a commercial transducer amplifier from BK Medical (Herlev, Denmark). As input waveform to the Field II model we measured the output voltage of the research amplifier. The peak voltage was limited to 31 V to avoid too high non-linear effects. We measured the hydrophone output from three transducer front elements by averaging 40 shoot sequences on each element using a remotely controlled Agilent MSO6014A oscilloscope. The pressure along the center line in a distance of 33 mm, 72 mm, and 112 mm from each element was measured as well as the intensity in the elevation plane in each depth.Results show that the 1D modeling of the linear transducer impulse response predicts the pulse waveforms satisfying. We show a root mean square error of approximately 26% on the pressure prediction and a root mean square error on the intensity prediction from 5.8–16.2% from 72 mm to 112 mm, and an average of 15.4% at 33 mm, when a 1.7 dB amplitude correction is made.

MEMS Electric-Field Probes for Laboratory Plasmas

This paper presents microfabricated sensors for directly measuring fine-scale plasma parameters in typical laboratory plasmas. Microfabricated probes have the potential to significantly advance basic plasma physics by enabling the measurement of fundamental processes under controlled conditions. Historically, the spatial scales of the finest electromagnetic-field fluctuations in laboratory plasmas have been too small for conventionally fabricated tools to sense. The new probes are arrays of electric-field sensors for measuring Debye-scale structures in the Large Plasma Device (LAPD) at the University of California at Los Angeles. Typical Debye lengths in the LAPD are 25 mum, with electron gyroradii of about twice that value. The probes are constructed of polyimide, chrome, and gold; have electrode widths ranging from 8 to 20 mum; are 23 mum thick; and are spaced 40 mum apart. The probes are wire bonded to a printed circuit board with commercial amplifiers, and the ensemble is placed inside the plasma chamber. The frequency response of the measurement system extends to 1 GHz. The probes have been used to measure the electric fields of interesting structures in the LAPD.

Performance of the Volterra behavioral model for wideband amplifiers

AbstractIn this article, we test the performance of a Volterra behavioral model for wideband amplifiers, which has been theoretically developed based on the frequency dependence knowledge of the nonlinear transfer functions. Relying on a simple measurement setup, a commercial driver amplifier has been extensively characterized at 915 MHz and modeled by using a WCDMA‐like probing signal at different power levels. The calculated values of the normalized mean square error (NMSE) versus the model memory length were compared with a standard memory polynomial (MP) model. To assess the accuracy of the model with other modulation formats, parameters extracted with the WCDMA‐like signal were used to predict the response for a 2‐MHz‐wide GSM‐like signal. For each memory length, the NMSE was calculated again and compared with the corresponding MP model. In all tested cases, results show that the proposed model exhibits a better performance even in the range of memory lengths, where both the models have a very similar number of coefficients. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2166–2169, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24542