Amplifier Output Research Articles

A new design strategy for bandwidth and efficiency enhancement in KA band CMOS power amplifier

PurposeThe purpose of this paper is to propose a new design strategy to enhance the bandwidth and efficiency of the power amplifier.Design/methodology/approachTo realize the introduced design strategy, a power amplifier was designed using TSMC CMOS 0.18um technology for operating in the Ka-band, i.e. the frequency range of 26.5-40 GHz. To design the power amplifier, first, a power divider (PD) with a very wide bandwidth, i.e. 1-40 GHz, was designed to cover the whole Ka-band. The designed Doherty power amplifier consisted of two different amplification paths called main and auxiliary. To amplify the signal in each of the two pathways, a cascade distributed power amplifier was used. The main reason for combining the distributed structure and cascade structure was to increase the gain and linearity of the power amplifier.FindingsMeasurements results for designed power dividers are in good agreement with simulations results. The simulation results for the introduced structure of the power amplifier indicated that the gain of the proposed power amplifier at the frequency of 26-35 GHz was more than 30 dB. The diagram of return loss at the input and output of the power amplifier in the whole Ka-band was less than −8dB. The maximum power-added efficiency (PAE) of the designed power amplifier was 80%. The output P1dB of the introduced structure was 36 dB and the output power of the power amplifier was 36 dBm. Finally, the IP3 value of the power amplifier was about 17 dB.Originality/valueThe strategy presented in this paper is based on the usage of Doherty and distributed structures and a new wideband power divider to benefit from their advantages simultaneously.

Phase characteristics of E class amplifier with various output networks

Phase shift of E class amplifiers with classical output network and output network that satisfies E class loading impedance conditions twice in the frequency band were studied by simulation and experimentally. The phase shift across switch in nominal operation mode was investigated analytically. The phase shift across switch in suboptimal class E operation mode that occurs while altering the operation frequency was investigated as well. The simulation method was the harmonic balance analysis using the switch model that considers the structure of power MOSFET device, namely, the existence of antiparallel diode pair that alters the switch current waveform. The input and transition capacitances of the transistor were considered. Experimental measurement of the phase shift was performed utilizing the recorded digitized waveforms of the switch input and output voltages by computing the phases of the voltages’ first harmonics with the help of Fast Fourier Transform. It was observed that characteristics of phase shift at switch output and amplifier output are dependent on the kind of load network. The relationship between the phase shift at the switch and hodograph of the loading impedance was demonstrated. For the network with double fulfilment of class E conditions that has a loop in the loading impedance hodograph the switch phase shift dependency has an extremum, which provides an opportunity to obtain the same phase shift at two frequencies within the operating frequency band. That facilitates control of the phase-frequency characteristic and the group delay of the amplifier. Knowledge of the phase-frequency dependency simplifies the conditions for calculation of the phase shift in the feedback network. The obtained results are useful for design of class E oscillator operating in a wide frequency band.

Pure-rotational 1D-CARS spatiotemporal thermometry with a single regenerative amplifier system.

We report spatiotemporal pure-rotational coherent anti-Stokes Raman spectroscopy (CARS) in a one-dimensional imaging arrangement obtained with a single ultrafast regenerative amplifier system. The femtosecond pump/Stokes photon pairs, used for impulsive excitation, are delivered by an external compressor operating on a ∼35% beam split of the uncompressed amplifier output (2.5 mJ/pulse). The picosecond 1.2 mJ probe pulse is produced via the second-harmonic bandwidth compression (SHBC) of the ∼65% remainder of the amplifier output (4.5 mJ/pulse), which originates from the internal compressor. The two pump/Stokes and probe pulses are spatially, temporally, and repetition-wise correlated at the measurement, and the signal generation plane is relayed by a wide-field coherent imaging spectrometer onto the detector plane, which is refreshed at the same repetition rate as the ultrafast regenerative amplifier system. We demonstrate 1 kHz cinematographic 1D-CARS gas-phase thermometry across an unstable premixed methane/air flame-front, achieved with a single-shot precision <1% and accuracy <3%, 1.4 mm field of view, and an excellent <20µm line-spread function.

Improved Error Correction Methods for Filterless Digital Class D Audio Power Amplifier Based on FCLNF

Aiming at correcting the error caused by the nonlinear and power supply noise of the bridge-tied-load (BTL) power stage of the filterless digital class D power amplifier, an error correction method was proposed based on feedforward power supply noise suppression (FFPSNS) and first-order closed loop negative feedback (FCLNF) techniques. This method constructed the first-order LCLNF loop for the power stage and further reduced the impact of the power supply noise on the power amplifier output by using FFPSNS technology to introduce the power supply noise into the feedback loop at the same time. The 0.35 μm CMOS process is used for analysis and comparison in Cadence. Cadence simulation results indicate that PSRR at the power supply noise frequency of 200 Hz is improved with 36.02 dB. The power supply induced intermodulation distortion (PS-IMD) components are decreased by approximately 15.57 dB and the signal-to-noise ratio (SNR) of the power amplifier is increased by 17 dB. The total harmonic distortion + noise (THD + N) of the power amplifier is reduced to 0.02% by FCLNF + FFPSNS.

Influence of annular electron beam uniformities on the microwave characteristics in an S-band relativistic klystron amplifier

The non-uniform annular electron beam models are established based on the annular cathode explosive emission luminescence images. The influence of electron beam uniformities on the microwave characteristics of an annular structure S-band relativistic klystron amplifier output cavity is investigated with particle-in-cell simulations. The electron beam non-uniformities are simulated using four different electron emission models: (1) continuous area without emission, (2) spaced emission, (3) enhanced emission, and (4) current density variation emission. The simulation results with the first emission model show that the output power decreases as the continuous area without emission increases, while the continuous area without emission has little effect on the frequency and pulse width. The simulation results with the second emission model show that the output power of the spaced emission is related to the distribution of non-emission areas. The more evenly the areas without emission are distributed on the annular cathode, the greater the output power is. The simulation results with the third emission model show that the higher the current density in the local area is, the smaller the output power is. The simulation results with the fourth emission model show that the fluctuation of current density causes the fluctuation of frequency and output power. The larger the change area of the current density is, the greater the fluctuation amplitudes of the output power and frequency are. The larger the fluctuation amplitude of current density is, the greater the fluctuation amplitudes of the output power and frequency are.

Optical parametric oscillator based on electro-optically polarization mode conversion

The back conversion of optical parametric oscillator seriously restricts its application in spectral analysis, optical holography, lidar and so on. The optical parametric amplifier output energy is simulated theoretically, and it is confirmed that the back conversion can be compensated by reducing the input energy of parametric light. An optical parametric oscillator with electro-optically polarization mode converter in the resonant is proposed to change the polarization state of the parametric light and adjust the proportion involved in the oscillation. The polarization mode conversion of MgO:PPLN crystal is analyzed theoretically. The experiment of energy regulatory structure is carried out. When the applied voltage of electro-optically polarization mode converter is 157 V/mm, the maximum output power of 1.47 μm and 3.84 μm are 4.4 W and 3.7 W, with a ratio of 1.2. It is confirmed that such structure can suppress back conversion and adjust the output ratio.

Multichannel fiber-optic amplifier at the wavelength of 1653 nm for lidar remote sensing of atmospheric methane concentrations

We have developed and tested a multichannel fiber-optic Raman-effect amplifier with peak output power of the order of 10 W operating at the wavelength of 1653 nm. This amplifier is intended for use in a remote-sensing lidar for atmospheric methane and consists of three power amplifiers, each with an output power of more than 3 W. The output from these amplifiers was combined in a fiber-optic multiplexer and then fed to the lidar transmitter collimator. Our modeling of a single power amplifier indicated that the Raman conversion efficiency is improved when thin-core optical fibers are used; a thin-core optical fiber can be used to decrease both the pump power and the length of the optical fiber. We describe the seed light source spectrum and the multichannel amplifier output spectrum. The output power can be increased beyond 20 W by multiplexing in another four power amplifiers, which would provide sufficient lidar transmitter power to measure gas concentrations from a spacecraft in low-Earth orbit.

A 28-GHz 16-Gb/s High Efficiency 16-QAM Transmitter in 65-nm CMOS

This work presents the design and implementation of an ultra-broadband quadrature common-mode amplitude modulator (QCAM) to generate high power back-off efficiency 16-QAM signals. The proposed QCAM transmitter consists of I- and Q-path PAM4 modulators, which digitally modulate the power amplifier (PA) output stage to relax the linearity requirement. An interleaved differential transformer-based coupler is proposed for wide-band combination of the baseband and LO signals. The I and Q PAM4 signals are combined using an on-chip Wilkinson power combiner to generate the 16-QAM output signal. The 28-GHz 16-QAM transmitter test chip, implemented in 65-nm CMOS, achieved measurement results of 11.35 dBm average RF output power, 9.2% DC-RF efficiency, 16 Gb/s data rate, and −24 dB EVM.

Imaging system with brightness amplification for a metal-nanopowder-combustion study

This work discusses an optical system with brightness amplification—a laser monitor, as well as the system's application for real-time imaging of the surface of metal nanopowders during high-temperature combustion. The advantage of the laser monitor is its combination of microscopic magnification, laser backlighting, and narrow-band filtering, which, together with high-speed video recording, makes it possible to visualize the nanopowder surface through the intense background lighting produced by a high-temperature burning sample. We used two laser-monitor schemes with short and long focal lengths to study the dynamics of the combustion process at different spatial resolutions. For compounds whose combustion is accompanied by intense scattering of the combustion products, we recommend using the laser monitor with increased monitoring distance via a mirror-imaging scheme. This proposed technique allows real-time monitoring of the high-temperature-combustion processes accompanied by intensive lighting and product scattering at a distance of 50 cm from the optical system. Both systems allow quantitative characterization of the combustion process by registering the average output of the brightness amplifier together with the overall brightness of glowing. The combustion of nanoAl + nanoFe and nanoAl + nanoFe + microAl powder mixtures was visualized using a laser monitor for the first time and compared with the combustion of aluminum nanopowder without additives.

Simulation and measurement of image charge detection with printed-circuit-board detector and differential amplifier.

We present a novel and thorough simulation technique to understand image charge generated from charged particles on a printed-circuit-board detector. We also describe a custom differential amplifier to exploit the near-differential input to improve the signal-to-noise-ratio of the measured image charge. The simulation technique analyzes how different parameters such as the position, velocity, and charge magnitude of a particle affect the image charge and the amplifier output. It also enables the designer to directly import signals into circuit simulation software to analyze the full signal conversion process from the image charge to the amplifier output. A novel measurement setup using a Venturi vacuum system injects single charged particles (with diameters in the 100 s of microns range) through a PCB detector containing patterned electrodes to verify our simulation technique and amplifier performance. The measured differential amplifier presented here exhibits a gain of 7.96 µV/e- and a single-pass noise floor of 1030 e-, which is about 13× lower than that of the referenced commercial amplifier. The amplifier also has the capability to reach a single-pass noise floor lower than 140 e-, which has been shown in Cadence simulation.

Digital background calibration technique for pipelined SAR ADCs with detect‐and‐switching algorithm

A digital background calibration technique for pipelined successive approximation register (SAR) analogue-to-digital converters (ADCs) with detect-and-switching (DAS) algorithm is proposed. The DAS algorithm exploits basic combinational logic to detect the first-stage conversion results, thereby determining whether to inject a random dithering signal. So as to reduce the amplifier's output swing and avoid the saturation of the second stage, the amplitude of the injected dithering signal is reduced by only injecting the capacitor mismatch into first-stage residue voltage. By executing the DAS-based calibration in the background, capacitor mismatch and inter-stage gain are obtained. Simulation results show that the signal to noise and distortion ratio is improved from 42.4 to 59.3 dB and spurious-free dynamic range is increased from 50.6 to 79.1 dB with calibration.

Brillouin Amplifier Noise Characterization by a Coherent Receiver and Digital Signal Processing

Brillouin amplification of a CW laser is evaluated by a coherent receiver and offline digital signal processing (DSP) to assess electric field distortions relevant to noise sensitive applications, and in particularly, optical communications. In this approach, the Brillouin amplifier output is heterodyne detected at the receiver so that the proportional electric field restored by DSP can be resampled into a virtual quadrature phase shift keyed (QPSK) signal. From this, an effective Q2 -factor distortion and amplitude and phase error are quantified. Characterization by the approach of Brillouin gain in a 4.46 km standard signal mode fiber shows amplitude error as the dominant noise feature while impact from phase error is generally negligible. Large gain a≥26 dB with minimal Q2 factor degradation <1 dB is observed achievable but with constraints on 1) input and 2) pump powers, and alignment of 3) frequency, and 4) state of polarization (SOP) for peak gain. Detuning of the SOP for minimum gain is observed to excite low frequency amplitude pulsations that grow in intensity and frequency with increasing pump power. For frequency detuning, signature amplitude and phase distortion patterns are uniquely visualized by the virtual QPSK constellations. Spectral analysis by DSP indicate an output carrier to noise ratio as being capped to a40 dB at 30 dB gain for the particular test fiber and noise as highly polarized. The characterized low noise and operating constraints of the Brillouin amplifier demonstrated by the approach aids design for noise sensitive applications.

Modelling of the laser amplification process with allowance for the effect of the temperature distribution in an Yb : YAG gain element on the thermophysical and lasing characteristics of the medium

A time-dependent three-dimensional model for the laser amplification process has been constructed with allowance for the effect of the temperature distribution on the thermophysical and lasing characteristics of gain media. We have performed numerical modelling of the laser amplification process in the gain elements of a two-stage subjoule-level cryogenic laser amplifier operating at a pulse repetition rate of up to 1 kHz. It has been shown that taking into account the temperature distribution is of critical importance in calculation of cryogenically cooled laser amplifiers pumped with high-power diodes. We have found optimal diode pump parameters at which the maximum achievable pulse energy at the amplifier output can reach 300 and 570 mJ at pulse repetition rates of 1000 and 500 Hz, respectively.

EVM Closed-Form Expression for OFDM Signals With Tone Reservation-Based PAPR Reduction

Peak to average power ratio (PAPR) reduction of OFDM signals has extensively been studied in the literature. Tone Reservation (TR) is one of the most famous algorithms and has already been included in some digital television standards such as DVB-T2 and ASTC3.0. However, the literature is still lacking theoretical analysis and performance bounds for the PAPR reduction of OFDM signals, especially using TR algorithms. For the first time, this paper provides fundamental results establishing the links between TR-PAPR reduction and the remaining signal distortions at the output of a non-linear high power amplifier (HPA) with and without memory effects. We first derive a generic EVM expression relying on the statistical characteristics of the samples composing the time domain signal and for any PAPR reduction technique. Computing these moments in the case of the quadratically constrained quadratic problem (QCQP) algorithm known as the optimal solution to the TR-PAPR reduction problem allows us to get the lower bound of the EVM of OFDM signals after TR-PAPR reduction and non-linear HPA. As a reference, we also provide the EVM expression using a clipping-based PAPR reduction method. The obtained EVM expressions have direct practical meaning since they are in function of the input power back-off (IBO) applied to the signal before the HPA. They also consist in a general analytical framework for OFDM PAPR reduction since they can be further exploited to analyze the performance of sub-optimal TR-based PAPR reduction algorithms.

Computer Simulation of Nonlinear Distortion of Class D Sound Amplifier on GaN-Transistors

Class A, B, AB and D amplifiers are used in the field of sound reproduction equipment, but each has its own peculiarities. The principle of operation of class D amplifiers is based on pulse width modulation. Transistors act as switches, either in the closed or opened state without intermediate values. The efficiency of real class D amplifiers is approximately 90%, in the most economical models 95%, and they have low dependence of the output power. The class D amplifiers are compact in size. For this paper, GaN-transistors were selected as the base. Because they are, compared to silicon transistors, low resistance in the open state, high breakdown voltage, higher switching speed of the transistors. They also work at high temperatures.The nonlinear distortions is negative features of Class D amplifiers. They directly affect the sound quality. The distortions include nonlinearity, which is determined by the modulation method and the "dead" period, which is necessary to prevent the occurrence of cross-current at the moment when both half-transistors are open. Modeling the parameters of a Class D amplifier, especially at an early stage of development, is a necessary tool that can significantly reduce the time and money spent on development and production. In this paper, simulations were performed using equivalent circle methods.Changing the shape of the signal at the output of the cascade is called nonlinear distortion. They affect the output signal formation positively (e.g. in demodulation) and negatively (e.g. in amplifiers). When investigating GaN transistors on Class D amplifiers, the signal shape at the amplifier output will be different from the signal shape at the input nonlinear distortions occur. They are due to the features of the structure of the amplifier.The purpose of this work is to create a model of the output stage of a class D amplifier on GaN transistors so as to be able to investigate the effect of nonlinear distortions when changing the switching frequency for different signal frequencies.The GaN transistor EPC2022 transistor based on GaN transducer, which is assembled on the EPC9035 board for researching, it was selected as the basis for the amplifier model.The simulation was performed in the Multisim 14.1 software environment. The dependence of the occurrence of nonlinear distortions for switching frequencies of 100 kHz, 250 kHz, 500 kHz, 1000 kHz for sound signals of 1 kHz, 2 kHz, 5 kHz and 10 kHz is investigated. The study founds that nonlinear distortions for different conversion frequencies have different frequency dependencies. For the studied conversion frequencies, there is a decrease in the distortion with increasing frequency, which is caused by the decrease of the high-frequency harmonics of the output filter.The optimal working conditions for obtaining the minimum values of the coefficient of nonlinear distortions are determined. It is investigated that the created model proves the efficiency of using class D amplifiers on GaN transistors for audio paths. Because it allows to obtain a coefficient of nonlinear distortion of up to 1% and high efficiency.

Switched-Capacitor Common-Mode Feedback-Based Fully Differential Operational Amplifiers and its Usage in Implementation of Integrators

For stabilizing the common-mode output voltage of fully differential operational amplifiers, switched-capacitor (SC) type of common-mode feedback (CMFB) is a familiar technique. This is appropriate for implementing high-gain wide-swing low-power op-amps due to its benefits of minimum power consumption, superior linearity across a large amplifier output swing range, and improved feedback loop stability in comparison to continuous-time CMFB. However, the usage of SC-CMFB requires careful attention to some realistic aspects, details of many of which are available in literature. Nonetheless, its adverse effect on the op-amp’s differential-mode gain has not been investigated much. The explanation for this effect is the SC-CMFB-induced equivalent resistive loading, and this is particularly significant in amplifiers like folded cascode which are intended to provide a high gain. This issue of drop in op-amp dc gain because of SC-CMFB, and the consequence on the realization of continuous-time and discrete-time forms of integrators utilizing such amplifiers is the topic of discussion in this paper. Relevant analytical derivations and circuit simulations at the transistor level are provided. A couple of design guidelines and circuit topologies for minimizing the loading-induced gain reduction are also presented.

Phase-locked two-color visible frequency comb system based on 1.5-μm all-polarization-maintaining fiber laser

A two-color visible frequency comb system based on a 1.5-μm all-polarization-maintaining (PM) fiber femtosecond laser was developed. This configuration relies on the implementation of three amplifiers, seeded by a single master oscillator. With the repetition rate (fr) of the oscillator locked to a reference frequency of 200 MHz, the output of the first amplifier was used to generate the feedback signal and achieve simultaneous phase lock of the carrier envelop offset frequency (fceo). The remaining two independently configurable amplifiers followed by highly nonlinear fibers and MgO-doped periodically poled lithium niobite crystals were used to produce visible comb lights at 543 and 633 nm (in air), respectively. By referencing to a hydrogen maser, the Allan deviations of fr and fceo at a gate time of 1 s are 438 μHz and 63 mHz, respectively. The spectral bandwidths of the 543- and 633-nm comb lights are 0.157 and 0.174 nm, respectively, and the single-mode powers of these comb lights are higher than 1 μW. The multiple-branch all-PM fiber-based visible frequency comb system exhibiting a narrow spectrum and a high single-mode power will facilitate the development of optical clocks and wavelength standard calibrations.

Numerical simulation of the thermal and hydraulic characteristics of the liquid heat exchanger of the APAA transmitter–receiver module

About 70% of the energy consumed by the T/R module is dissipated as heat and leads to poor performance and reliability of the antenna system. The problem of heat removal from T/R modules is thus an acute one. This paper presents the results of numerical simulation of thermal and hydraulic characteristics of a promising basic supporting structure based on a cold plate for a multi-channel T/R module. Each of the two mounting surfaces of the cold plate carries four high-power output amplifiers and one unit with low-power electronic components. Each power amplifier contains two active microwave elements with a heat dissipation power of 11 W each.The heat dissipation power of each unit with low-power electronic components is 50 W. The total power of the T/R module is 276 W. The T/R module is cooled by pumping working fluid (Antifreeze 65 with an inlet temperature of 50 °C) through the cooling channel of the cold plate. The flow rate of the fluid varied in the range from 1 to 11 l/min. The simulation allowed obtaining the temperature field distribution of the mounting surfaces of the cold plate and the working fluid flow rates that provide effective cooling of the mounting surfaces at an acceptable hydraulic resistance in the fluid channel. It was shown, for example, that at a fluid flow rate of 3 l/min, the temperature at the installation sites of active microwave elements did not exceed 66 °C, and the pressure drop was less than 4000 Pa.

Multi-Channel Neural Recording Implants: A Review.

The recently growing progress in neuroscience research and relevant achievements, as well as advancements in the fabrication process, have increased the demand for neural interfacing systems. Brain–machine interfaces (BMIs) have been revealed to be a promising method for the diagnosis and treatment of neurological disorders and the restoration of sensory and motor function. Neural recording implants, as a part of BMI, are capable of capturing brain signals, and amplifying, digitizing, and transferring them outside of the body with a transmitter. The main challenges of designing such implants are minimizing power consumption and the silicon area. In this paper, multi-channel neural recording implants are surveyed. After presenting various neural-signal features, we investigate main available neural recording circuit and system architectures. The fundamental blocks of available architectures, such as neural amplifiers, analog to digital converters (ADCs) and compression blocks, are explored. We cover the various topologies of neural amplifiers, provide a comparison, and probe their design challenges. To achieve a relatively high SNR at the output of the neural amplifier, noise reduction techniques are discussed. Also, to transfer neural signals outside of the body, they are digitized using data converters, then in most cases, the data compression is applied to mitigate power consumption. We present the various dedicated ADC structures, as well as an overview of main data compression methods.

Flexible chirp-free probe pulse amplification for kHz fs/ps rotational CARS

The sensitivity of high-repetition-rate hybrid femtosecond/picosecond (fs/ps) rotational coherent anti-Stokes Raman scattering (RCARS) is strongly influenced by the energy available for the ps probe pulse. In this work, a high-energy ps probe pulse that is time-synchronized with the fs pump/Stokes pulse is achieved by using a diode-pumped Nd:YAG amplifier seeded at 1064.4 nm by the output of a fs optical parametric amplifier. Nearly transform-limited, 10 ps pulses with up to 800 µJ/pulse and a bandwidth of 1.9 c m − 1 were generated at the second harmonic 532.2 nm and used for kilohertz-rate fs/ps RCARS thermometry up to 2400 K with accuracies of 1–2%. We furthermore demonstrate the amplification of variable pulsewidths for flexible single-mode (chirp-free) RCARS signal generation.