Small Signal Gain Research Articles

Detailed investigation of absorption, emission and gain in Yb:YLF in the 78–300 K range

We present spectroscopic measurements focusing on a detailed investigation of temperature dependence of absorption, emission and gain in the uniaxial Yb:YLF laser gain medium. Measurements are carried out in the 78–300 K range, but we especially targeted our attention to the 78–150 K interval, which is the desired working range of liquid nitrogen cooled cryogenic Yb:YLF lasers/amplifiers. A tunable (770–1110 nm) Cr:LiSAF laser with around 100 mW continuous-wave output power and sub-0.2 nm bandwidth is used as an excitation source. The average power of the Cr:LiSAF laser is low enough to prevent heating of the sample, and its spectral flux (W/nm) is high enough to enable large signal-to-noise ratio measurements. Measured absorption data is used to cross-check the validity of the emission measurements, while the measured temperature dependent small-signal gain profile provided a second independent confirmation. The acquired absorption cross section curves match the previous literature quite well, whereas the measured strength of c-axis emission is stronger than some of the earlier reports. Direct measurements of small signal gain confirmed the emission cross section data, where single pass gain values above 50 have been measured for the 995 nm transition of E//c axis at 78 K. We further provide simple analytic formulas for the measured temperature dependence of absorption and emission cross section. We hope the presented results to be useful for the development of next generation of cryogenic Yb:YLF laser and amplifier systems.

Fully integrated CMOS tunable power amplifier using reconfigurable input/interstage/output matching networks

This paper presents a two-stage tunable power amplifier (PA) fully-integrated in 130 nm CMOS process. This multi-band PA consists of reconfigurable input, interstage, and output matching networks in order to tune the center frequency in use. The proposed tunable power amplifier enables three different bands with center frequency of 900 MHz, 1450 MHz, and 1900 MHz. By switching these bands, the designed power amplifier covers frequency range of 700 MHz–2200 MHz known as Long-Term Evolution mobile network. As a result, the proposed tunable power amplifier obtains small-signal gain (S21) of 27.8 dB/29.4 dB/28.6 dB, saturated output power (Psat) of 22.4 dBm/23.0 dBm/23.2 dBm, and power added efficiency of 21.0%/23.7%/25.0% at three targeted frequency bands, respectively. The proposed fully-integrated triple-band power amplifier chip layout occupies an area of 2.25 mm2 including bond pads.

A D-Band Power Amplifier in 65-nm CMOS by Adopting Simultaneous Output Power-and Gain-Matched Gmax-Core

This paper proposes a simultaneous output power- and gain-matching technique in a sub-THz power amplifier (PA) design based on a maximum achievable gain ( G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) core. The optimum combination of three-passive-elements-based embedding networks for implementing the G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> -core is chosen considering the small- and large-signal performances at the same time. By adopting the proposed technique, the simultaneous output power- and gain-matching can be achieved, maximizing the small-signal power gain and large-signal output power simultaneously. A 150 GHz single-ended two-stage PA without power combining circuit is implemented in a 65-nm CMOS process based on the proposed technique. The amplifier achieves a peak power gain of 17.5 dB, peak power added efficiency (PAE) of 13.3 and 16.1 %, saturated output power ( P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> ) of 10.3 and 9.4 dBm, and DC power consumption of 86.3 and 52.4 mW, respectively, under the bias voltage of 1.2 and 1 V, which corresponds to the highest PAE, gain per stage and P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> per single transistor among other reported CMOS D-band PAs.

An ESD and Interference-Robust Protection Circuit for Cascode Low-Noise Amplifier in CMOS-SOI Technology

In this paper, we propose a double diode network including an additional stacked diode, which provides robustness against Electrostatic discharge (ESD) and high-frequency interference signals. The proposed stacked diode in the conventional double diode network protects the integrated circuit from instantaneous voltage events by providing an additional current path to the double diode network. Also, it can structurally minimize the parasitic capacitance generated in the diode. The general operating principle and limitation of the conventional double diode network for ESD events and high-frequency interference signals were analyzed and simulated. For experimental verification, a cascode LNA with inductive source degeneration was designed in a 130nm CMOS Silicon-on-insulator (SOI) process for the time-division long-term evolution (TD-LTE) application at the coexistence band. The LNA with the proposed double diode network provides a noise figure of 1.08 dB and a small-signal gain of 18.7 dB at 2.65 GHz (Band 41). And it was measured to be able to protect the internal circuit at 2000 V HBM event, and the RF performances were not affected even with a high-frequency interference signal close to 30 dBm.

Design of 35-dB 0.03-to-2.7 GHz Two-Stage Broadband Power Amplifier With 37.2 dBm Psat Using Modular Technology

This paper presents a modular technology for two-stage broadband power amplifier (PA) design. The proposed method focuses on separately realizing two stage’s flat gain characteristics, thus providing the entire circuit’s required flatness over broad bandwidth. The power stage employs stacked structure to provide enough power and confine the output impedance around $50~\Omega $ , while the driver stage’s periphery is selected to achieve impedance transformation demanded by modularization. The elaborate requirements for input and inter-stage matching networks (MNs) are repeatable which can be synthesized by real frequency technique (RFT), shortening the design time of broadband MNs. The modular approach can also be transferred to the implementation of other broadband PAs. This novel technology was verified using $0.25~\mu \text{m}$ GaAs PHEMT process. The fabricated two-stage broadband PA obtains a small-signal gain higher than 35.0 dB and saturated output power of 37.2± 1.6 dBm from 30 MHz to 2.7 GHz, with a peak power added efficiency (PAE) of 46.2% at 500 MHz. To our knowledge, this is the highest gain and output power in GaAs broadband amplifier below 2.7 GHz.

An mm-Wave Multi-Mode Asymmetric Power Amplifier With Back-off Efficiency Enhancement

This paper presents a multi-mode asymmetric power amplifier (MMA-PA) with back-off efficiency enhanced. The back-off efficiency is improved without a lossy impedance inverter or signal separator which is used in conventional Doherty or outphasing amplifiers. The design considerations are provided in detail. In addition, the proposed MMA-PA operates in three different modes according to the input power level. The PA is fabricated in a 65-nm bulk CMOS technology. In the high-power (HP) mode, the MMA-PA exhibits a small-signal gain of 18.4 dB at 30 GHz and a 3-dB bandwidth of 4.5 GHz from 27.7 to 32.2 GHz. The output saturation power ( $\text{P}_{\text {sat}}$ ) and 1-dB compression power are 16.7 and 15.1 dBm, respectively. While the peak power-added efficiency (PAE) is 24.7 %, the 6-dB back-off PAE keeps a high value of 14.1 %. In the medium-power (MP) mode, $\text{P}_{\text {sat}}$ and peak PAE are 12.3 dBm and 21 %, respectively with a similar gain of 18.9 dB. In the low-power (LP) mode, the gain, $\text{P}_{\text {sat}}$ and peak PAE are 11.5 dB, 7.5 dBm and 16.5 %, respectively. With a 100-MHz 64-QAM OFDM signal following the 3GPP 5G NR standard, the average output power in the HP mode is 6 dBm with EVM of −26 dB and ACLR < −34 dBc. In the MP and LP modes, the average output power are 3.3 and 1.1 dBm, respectively with EVM of −26.6 and −26.1 dB.

Simulation and experimental results of a high-gain two-stage and double-pass off-axis Nd:YVO4 picosecond laser amplifier.

A high-gain two-stage double-pass off-axis Nd:YVO4 picosecond laser amplifier has been developed. The comprehensive influence of crystal doping concentration and pump beam quality on the small-signal gain of the Nd:YVO4 amplifier is theoretically analyzed with a model developed by considering energy transfer upconversion and pump light absorption saturation effect. The thermal effect of Nd:YVO4 crystal with different doping concentrations, undoped end cap lengths, and pump beam quality is investigated as well. Based on the theoretical analysis, a high-gain two-stage and double-pass off-axis Nd:YVO4 amplifier based on picosecond fiber seed source is realized by choosing long-composite low-doping Nd:YVO4 crystal and with high brightness laser diode pumping, delivering a gain of 28 dB and an output pulse energy of 67.5 µJ at a repetition rate of 200 kHz.

A 52–58 GHz Power Amplifier With 18.6-dBm Saturated Output Power for Space Applications

This brief presents a 52–58 GHz power amplifier (PA) with constant output power across the entire band. A new topology based on the impedance transformation of transmission lines was adopted as the inter-stage matching network. Compared with the conventional 2-section LC matching topology, our approach reduced the matching loss by 1.5 dB at 54 GHz. Such topology made the design capable of operating at a frequency close to 80% of the unit-current-gain cut-off frequency ( $f_{T}$ ) specified by the device technology. Additionally, stacked-FET was adopted as the power stage for the output power enhancement in a broadband sense. Implemented in the commercially available 0.15- $\boldsymbol{\mu }\text{m}$ GaAs pseudomorphic high-electron-mobility transistor (pHEMT) process, the 2-stage PA demonstrated a small-signal gain of 14.7 dB, a saturated output power ( $P_{sat}$ ) of 18.6 dBm, and a maximum power-added-efficiency (PAE) of 18.2% at 54 GHz.

Design of 74% Fractional Bandwidth Continuous-Mode Doherty Power Amplifier Using Compensation Susceptance

This brief presents a novel design method of broadband continuous-mode Doherty power amplifier (CM-DPA) using compensation susceptance. In particular, at power back-off point, the compensation susceptance is added at the current source plane of the carrier PA to make it operates in continuous mode, which thus enhances the back-off efficiency and extends the bandwidth. Meanwhile, considering the influence of the parasitic parameters of the PA in practical design, the designed compensation susceptance at the current source plane is equivalently transformed into the compensation susceptance at the package plane of the carrier PA. Additionally, at saturation point, the load impedances at the package plane of both carrier and peaking PAs can meet the impedance conditions of drain efficiency more than 60%. Based on the proposed method, a 74% fractional bandwidth CM-DPA operating from 1.1 to 2.4 GHz is designed and measured. Under the continuous-wave excitation, the measured 6-dB back-off efficiency is 46.8%-63% and the saturation efficiency is 59.1%-78.8%. The measured small-signal gain and back-off gain are 10-12 dB and 9.1-10 dB, respectively.

Experimentally investigating the degradations of small-signal gain for a GaN class-AB dual-band power amplifier under high temperature and humidity conditions

In order to get the high temperature and humidity characteristics of key specifications for a power amplifier (PA), the degradation of the small-signal gain for a GaN class-AB dual-band PA under different temperature and humidity conditions is investigated experimentally. The experimental results show that the small-signal gain of the GaN class-AB dual-band PA will decrease under high temperature and humidity conditions. The main reasons for this degradation are discussed and analyzed in this paper.

고출력 GaN RF 전력증폭 소자 공정 양산 개발

In this report, the results of a government supported project have been summarized. The purpose of the project was to develop a fabrication process of high power GaN RF devices with 0.4 um gate length at S-band frequency ranges. The most important fact which makes this project different from previous government funded projects on GaN HEMT device development in Korea is that this project is not only asking for the performance of the device but also for the reliability and yield of the devices which are the two crucial factors for manufacturing and mass production. Through the hard work for the last 5 years, GaN HEMT process has been developed in Wavice Inc., and it shows excellent performance and reliability. The process control monitoring devices with 0.7 mm gate periphery show −2.7 V threshold voltage, &gt;200V breakdown voltage, 950 mA/mm maximum saturation current, 250 mS/mm maximum trans-conductance, 19 GHz ft, 41 GHz fmax, 16.5 dB small signal gain, 8W/mm maximum output power density, 53% power added efficiency. The RF performances of PCM devices were measured with continuous wave mode. The high power devices were fabricated by connecting unit cell devices with 3.5 mm gate periphery in parallel. 3.5 mm devices show &gt;20W output power and 3.5x8=28 mm devices show &gt;186.5W output power, &gt;13.5dB small signal gain, &gt;63.5% drain efficiency over 400 MHz bandwith in S-band with pulsed input signal with 15% duty cycle.. Both unit cells and 180W high power devices passed MIL-STD based reliability tests. The 180W devices shows 83~92% yield from the on wafer test.

A Broadband 110–170-GHz Stagger-Tuned Power Amplifier With 13.5-dBm P sat in 130-nm SiGe

This letter presents a fully integrated three-stage single-ended D-band power amplifier (PA) designed in 0.13-μm silicon-germanium (SiGe) BiCMOS technology. Several bandwidth extension techniques and matching networks are mutually exploited to maximize Bandwidth (BW) performance while assuring unconditional stability. Its measured 3-dB bandwidth covers the entire D-band (110-170 GHz). The PA has a small-signal peak gain of 21 dB at 151 GHz. Its saturated output power (P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> ) in the D-band varies from 11.8 to 13.9 dBm and its output referred 1-dB compression point (OP1 dB) from 9.2 to 12.5 dBm within the D-band. The presented amplifier occupies 0.65 × 0.47 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (including pads) and draws a current of 115 mA from a 3.3-V supply. To the best of our knowledge, these performances represent the state of the art in silicon technology with a minimum (P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> ) of 11.8 dBm and (OP1 dB) of 9.2 dBm covering the entire D-band.

A 24–30 GHz 31.7% Fractional Bandwidth Power Amplifier With an Adaptive Capacitance Linearizer

A two-stage 24-30 GHz wideband power amplifier (PA) with an adaptive capacitance linearizer is presented, which is fabricated using a 28-nm bulk CMOS process. Staggered input gain matchings of the driver and power stages are implemented with wideband output power matchings to achieve wideband power characteristics. An adaptive capacitance linearizer is introduced at the power stage input to improve the AM-PM linearity with respect to input powers. At 24/26/28/30 GHz, it achieves 19.7/20.3/20/20 dBm P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sat</sub> , 18.2/18.2/17.8/17.2 dBm P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1dB</sub> , and 34.5/33.1/30/30.3% peak power added efficiency (PAE). The small-signal gain of 21.2 dB and the 3-dB bandwidth of 8.2 GHz are achieved. It has a core size of 0.189 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Amplification properties of polycrystalline Fe:ZnSe crystals for high power femtosecond mid-IR laser systems

Abstract In this Letter, a multi-pass amplifier based on polycrystalline Fe:ZnSe element grown by the chemical vapor deposition (CVD) method and doped through diffusion technique is realized with output energy of more than 3 mJ at 4.5 μm. The crystal used in the experiment has external doping layers with peak Fe ions concentration of (1-2)х1019 сm−3 located on the surface and Fe ions diffusion depth of hundreds of microns. The crystal demonstrates small-signal gain per pass of 5.7 (corresponding to effective gain of 7.1 cm−1 taking into account 8 mm total length of the crystal) for short pump pulse (40-ns) under the optimal pump fluence of around 0.8 J/cm2 and upper-level lifetime of 670 ± 10 ns under moderate cooling to 7-8 °C, which makes such a crystal very attractive for mid-IR femtosecond multi-pass amplifiers and generators. Moreover, properties of the polycrystalline Fe:ZnSe elements grown by CVD and doped through diffusion and CVD methods with higher Fe ions concentration are also studied at different temperatures and compared with a single crystal element.

LD end-pumped joule-level square-rod Nd:glass laser amplifier with high efficiency

This paper presents a laser diode (LD) end-pumped square-rod Nd:glass laser system capable of achieving joule-level output energy at 1-Hz repetition rate. The laser system generated 966 mJ of energy in a 5-ns pulse for a pumping energy of 9.66 J at 802 nm, corresponding to an optical-to-optical conversion efficiency of 10%, which is higher than those of similar existing systems. A single-pass small-signal gain of 2.54 and pulse energy stabilities of 2.5% (peak-valley) and 0.37% (root-mean-square) were achieved by eight-pass amplification. The output energy of 966 mJ was generated, and the near-field modulation of 90% beam aperture was 1.37; further, the 82.5% far-field energy concentration was 2.5 times higher than the diffraction limit. The measured single-pass thermally induced wavefront aberration (1.15λ) was similar to that calculated using the thermal model. The beam quality could be further improved using adaptive phase corrector technology.

A 60-GHz SiGe Power Amplifier With Three-Conductor Transmission-Line-Based Wilkinson Baluns and Asymmetric Directional Couplers

A compact, 60-GHz high-power, wideband balanced power amplifier, implemented in a 90-nm SiGe BiCMOS technology, is demonstrated. A three-conductor transmission-line-based asymmetric coupled-line directional coupler is used to achieve impedance transformation and quadrature power combining simultaneously. A Wilkinson balun based on a three-conductor transmission line structure is implemented to achieve a four-way series-parallel power combining. Analyses of the three-conductor asymmetric coupler and the Wilkinson balun combiner are provided in this article. The design achieved 17.3-dB small-signal gain, with 41.8-GHz 3-dB bandwidth, from 28.1 to 69.9 GHz. A 24.4-dBm saturated output power (PSAT) was measured at 60 GHz with a 22-GHz 1-dB P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SAT</sub> bandwidth, covering 45-67 GHz. The circuit showed a peak power-added efficiency (PAE) of 14.2% at 60 GHz, and the peak PAE is above 11.5% across the 1-dB P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SAT</sub> bandwidth. The proposed eight-way power combining scheme achieves 0.077-mm2 per-way area consumption and 449-mW/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> power density.

Luminescence of Xe2Cl* upon laser excitation of Cl2 – Xe mixtures in a wide pressure range

The luminescence of Xe2Cl* excimer upon optical excitation of high-pressure Cl2 – Xe mixtures by XeCl laser pulses (λ = 308 nm) with different energies is investigated. It is shown that small-signal gain of the Xe2Cl amplifier may reach ∼1.3 × 10−1 cm−1 in a mixture of Cl2 and Xe with partial pressures of 4 Torr and 9 atm, respectively, and an excitation fluence of 1026 photons cm−2 s−1.

Pulsed-pump phosphorus-doped fiber Raman amplifier around 1260 nm for applications in quantum non-linear optics.

We describe a fiber Raman amplifier for nanosecond and sub-nanosecond pulses centered around 1260 nm. The amplification takes place inside a 4.5-m-long polarization-maintaining phosphorus-doped fiber, pumped at 1080 nm by 3-ns-long pulses with a repetition rate of 200 kHz and up to 1.75 kW peak power. The input seed pulses are of sub-mW peak-power and minimal duration of 0.25 ns, carved out of a continuous-wave laser with sub-MHz linewidth. We obtain linearly polarized output pulses with peak powers of up to 1.4 kW, corresponding to peak-power conversion efficiency of over 80%. An ultrahigh small signal gain of 90 dB is achieved, and the signal-to-noise ratio 3 dB below the saturation power is above 20 dB. No significant temporal and spectral broadening is observed for output pulses up to 400 W peak power, and broadening at higher powers can be reduced by phase modulation of the seed pulse. Thus, nearly-transform-limited pulses with peak power up to 1 kW are obtained. Finally, we demonstrate the generation of pulses with controllable frequency chirp, pulses with variable width, and double pulses. This amplifier is thus suitable for coherent control of narrow atomic resonances, especially for the fast and coherent excitation of rubidium atoms to Rydberg states. These abilities open the way towards several important applications in quantum non-linear optics.

A novel H-plane loaded on a double-staggered grating waveguide slow-wave structure for W-band traveling-wave tubes

A novel H-plane loaded on a double-staggered grating waveguide (DSGW) slow-wave structure (SWS) is proposed. The main advantage of this SWS is its high interaction impedance and low phase velocity, based on which higher output power can be expected. Electromagnetic characteristics and particle-in-cell simulations were performed using CST Microwave Studio software. The dispersion diagram of the SWS was optimized for a central frequency of 94 GHz which corresponds to a beam voltage of 13.2 kV in the second spatial harmonic (2 $$\pi$$ –3 $$\pi$$ ). A sheet electron beam with a current of 200 mA is used to interact with the longitudinal electric field. The reflection signal at the input port is below −15 dB for frequencies of 89–98 GHz and a small-signal gain of 35 dB is achieved at the output port for a tube length of 80 mm.

Investigation of the process of mixing reagents in the laser chamber of active medium generators of continuous-wave chemical lasers with promising nozzle arrays

It is shown that the use of a toothed nozzle array in the active medium generator (AMG) of continuous-wave chemical lasers (CWCLs) allows more efficient mixing of reagents to be achieved in the laser chamber than in an AMG with a slit nozzle array. The results of calculations of parameters of the active medium of a DF CWCL operating in the gain regime for the AMG with traditional and promising nozzle array designs are presented. A kinetic model of processes in the DF CWCL active medium is proposed, which allows obtaining a good agreement with the results of measurements of the small-signal gain.