Small Signal Gain Research Articles

Efficient diode-pumped Er:YAP master-oscillator power-amplifier system for laser power improvement at 2920 nm

We report on the first demonstration of laser-diode-pumped master-oscillator power-amplifier (MOPA) system based on Er-doped bulk material working at 2920 nm. The relaxation oscillation at the beginning of the laser pulse from the Er:YAlO3 (YAP) oscillator was suppressed effectively when the pump frequency was increased to 140 Hz, as a result of the establishment of a three-level system. In the amplifier, the small signal gain of the Er:YAP strongly depends on pump duration and repetition frequency, and can reach the upper limit of parasitic oscillation. Further, 25.5 mJ of output pulse energy has been achieved from the amplifier at 150 Hz frequency (2.2 ms pump duration), with over 32% of optical-to-optical efficiency. Further improvement of the amplification ability of the MOPA system was discussed.

Study on the 400 mm 4 × 2 combined slab amplifier system

This paper provides the experiment results of a 400 mm 4 × 2 combined slab amplifier system for high-power laser devices based on a new pumping configuration, which involves 37 nm-diameter pulse xenon lamps, a multilamp arrangement, an operating voltage of 31 kV and a uniform pumping arrangement comprising 12 and 14 xenon lamps in the middle and side flashlamp cassettes, respectively. The experimental results show that the small signal gain coefficient was 5.60% cm−1. The pump-induced wavefront distortion accumulated by six slabs of Nd:glasses is 1.37λ peak-valley (PV) and the pointing offset value of pump beam is about 0.32 μrad/slab/pass. After discharging, the system was purged with clean gas at 0.4 m s−1. The cleanliness in the cavity returned to level 100 within 20 s, and the heat recovery time of the system was about 2 h.

Numerical study of a hybrid mode-locked erbium-doped fluoride fiber laser at 2.8 μm

We numerically investigate a hybrid mode-locked erbium-doped fluoride fiber laser in the mid-infrared region. Based on the coaction of nonlinear polarization rotation (NPR) and semiconductor saturable absorber mirror (SESAM), uniform mode-locked soliton pulse with 155 fs pulse duration, 14.78 kW peak power, and 2.29 nJ pulse energy can be achieved. For comparison, the single SESAM mode-locking and NPR mode-locking of the erbium-doped fluoride fiber laser are simulated, respectively. The effect of all kinds of parameters including gain fiber length, saturable energy of the gain fiber, linear cavity phase delay bias, and small-signal gain on the hybrid mode-locking laser are also investigated.

A 24–44 GHz Broadband Transmit–Receive Front End in 0.13-μm SiGe BiCMOS for Multistandard 5G Applications

In this article, a novel broadband millimeter-wave (mm-wave) front end (FE) based on the asymmetric switch network structure is proposed for multistandard fifth-generation (5G) applications. The asymmetric switch network consists of a bidirectional impedance transformation network and a T-type topology single-pole single-throw (SPST) switch. In the TX-mode, the bidirectional impedance transformation network serves as an output matching network to achieve a continuous-mode Class-F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> power amplifier (PA) to expand the bandwidth. In the RX-mode, the OFF impedance of the PA can be transformed into a high-impedance region by the bidirectional impedance transformation network. Based on the proposed structure, a broadband mm-wave front end is implemented in the 0.13- μm SiGe BiCMOS process, which occupies 906 μm ×997 μm including pads. In the TX-mode, 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 of the FE covers 21-44 GHz with the maximum output power of 18.1-19 dBm and the peak power added efficiency (PAE) of 20.2%-26.8%. In the RX-mode, the FE achieves an 84.6% and -3-dB small-signal gain fractional bandwidth from 20.2 to 49.8 GHz with 38-mW power consumption. It achieves a measured noise figure (NF) of 7.62-11.64 dB over the frequency range of 24-48 GHz. To the best of our knowledge, this is the first FE that covers all the present 5G mm-wave bands without reconfiguration.

Temperature dependence of the small-signal gain of a Cr3+ and Nd3+ co-doped Y3Al5O12 ceramic

There is a demand for higher-efficiency neodymium and chromium co-doped yttrium aluminum garnet (Nd/Cr:YAG) ceramics that can be excited by broadband light sources, such as flash lamps. We experimentally investigated the temperature dependence of the gain coefficient of a Nd/Cr:YAG ceramic (Nd: 1.0 at%, Cr: 2.0 at%). The gain coefficient at 1064 nm decreased with increasing temperature when Nd3+ was directly excited at 808 nm. However, when Nd3+ was excited via energy transfer from Cr3+ excited at 610 nm, the gain coefficient increased with increasing temperature. This temperature dependence was theoretically explained by solving the rate equations for Nd/Cr:YAG. Nd/Cr:YAG ceramics pumped with flash lamps may provide good laser performance without loss of gain even at high temperatures.

Design of a K-Band High-Efficiency Power Amplifier in 45 nm SOI CMOS Technology

This paper presents a high efficiency K-band CMOS power amplifier (PA) in GlobalFoundries (GF) 45 nm SOI CMOS technology for 5 G applications. Compared with an ordinary two-stage PA, the PA uses a current-reused technique to enhance the power gain and efficiency within the frequency band. The resistance feedback structure of the power output stage improves the gain flatness and the output bandwidth, and reduces the matching components. The simulation results show that the output power (Pout) is more than 21.6 dBm from 18 to 27 GHz, while the small signal gain (S21) is more than 30.6 dB, the output 1 dB compression point (OP1dB) is 19.8 dBm and power-added efficiency (PAE) is 36.8%. With a 64-QAM LTE signal with 20-MHz bandwidth, adjacent channel leakage ratio (ACLR) is −31.2 dBc and the error vector amplitude(EVM) is less than − 26.7 dB at an average output power of 10.9 dBm. The chip area with pads is 0.75mm2, and consumes 15.1 mW from 2.4 V.

High Linear Power E-Band Traveling-Wave Tube for Communication Applications

A low-voltage and high linear power E-band traveling-wave tube amplifier is designed to meet the demand of high-data-rate wireless communication. The integrated design, including the dispersion combination of folded waveguide slow wave structure, broadband diamond pillbox window, and AlN-SiC lumped attenuator, ensures the success of the prototype tube with satisfying performance. The test results show that the amplifier is capable of providing more than 45.2 W output power, 38.8 dB saturated gain, 14.3% total efficiency, and 45.6 dB small-signal gain in 71-76 GHz band with a low voltage of 12.88 kV and a current of 80 mA. The 1 dB compression point exceeding 20 W verifies the feasibility of dispersion combination technology for high linear power design.

Lamp-pumped eight-pass neodymium glass laser amplifier with high beam quality

This study presents a lamp-pumped Nd:glass laser system capable of achieving joule level output energy at 1-Hz repetition rate with high beam quality. The 1.8 J of energy in a 5 ns pulse was achieved with 1.5 mJ injected energy. The laser system includes a beam shaping module and an eight-pass, lamp-pumped amplifier. The laser amplifier demonstrated long-term energy stability of 1.76% PV and 0.29% RMS when operating at 1.8 J for 30 minutes. In a longer period of operation, no damage or obvious beam degradation was found. A uniform gain distribution with a single-pass small-signal gain of 3.89 was acquired with the four-lamp-pumping method, and thermally induced wavefront aberration was mitigated. Finally, a high beam quality was obtained using a homemade optically addressed liquid crystal light valve. After compensation, the near-field modulation decreased from 1.38 to 1.21, meanwhile, the beam contrast decreased from 6.54 to 4.71%. In terms of the far-field quality, a 90% far-field energy concentration was 2.5 times the diffraction limit.

Ka-band time-domain multiplexing front-end with minimum switch area utilization on 22 nm fully depleted silicon-on-insulator CMOS technology

AbstractA time-domain duplexing radio frequency (RF) front-end with integrated antenna switch, power amplifier (PA), and low noise amplifier (LNA) was developed aiming for fifth-generation communication (5G) applications covering 24–28 GHz frequency range. Antenna switch utilizes pre-existing LNA input matching network together embedded with grounded shunt transistor switch to provide sufficient isolation of receive side from PA. Respectively, high impedance of off-state PA is assumed to achieve acceptable receive performance. Resulting output power is 13.6 dBm with 15 dB of peak small-signal gain at 28 GHz. Maximum average channel power was 4.8 dBm with 100 MHz 64-QAM OFDM signal within 5G adjacent channel power ratio and error vector magnitude specifications. Receive (RX) front-end achieves 5 dB noise figure at 24 GHz and 7 dB of peak gain. Performances of amplifiers degraded only by 2 dB from switch integration. The front-end dissipates 183 and 4.6 mW of power in transmit and receive mode, respectively. The simplistic design method minimizes cost both in circuit area (only 0.19 mm2) and design time making this front-end an attractive alternative in massive phased array applications using 22 nm complementary metal oxide semiconductor (CMOS) fully depleted silicon on insulator process.

Comparison of 1480 nm and 980 nm-pumped Gallium-Erbium fiber amplifier

Background: One way to reduce the length of the gain medium in Erbium-Doped Fiber Amplifier (EDFA) is by doping the fiber core with a high concentration of Erbium. However, this method caused ion clustering effects, which limits the EDFA’s efficiency. In this research, the use of Gallium as a new co-dopant in erbium-doped silica fiber is explored. Methods: The new fiber, namely Gallium co-doped Erbium fiber (Ga-EDF), is used as a gain medium in an optical fiber amplifier setup. A 2-meter length of the Ga-EDF fiber was used in a single pass configuration with a forward pumping scheme at 150 mW pump power. The Ga-EDF amplifier's gain and noise figure while pumping at 980 nm and 1480 nm were compared. The amplifier's performance was evaluated as the input signal power varied between -30 dBm to 3 dB, over the wavelength range of 1520 nm to 1580 nm. Results: The 980 nm-pumped Ga-EDF amplifier achieved the maximum small-signal gain of 22.45 dB and the corresponding noise figure of 5.71 dB at the input signal wavelength of 1535 nm. Meanwhile, the 1480 nm-pumped Ga-EDF amplifier attained the maximum small-signal gain of 20.83 dB and the corresponding noise figure of 5.09 dB at the input signal wavelength of 1550 nm. At the input signal power below -20 dBm and the wavelength range 1520 nm to 1547 nm, the Ga-EDF performs better when pumped at 980 nm. Their performance is comparable at the input signal wavelength range between 1547 nm to 1580 nm. At the input signal power above -20 dBm, the 1480 nm-pumped Ga-EDF outperformed the 980 nm-pumped amplifier. Conclusions: The overall performance indicates that the gain saturation point of the 1480 nm-pumped amplifier is higher than the 980 nm-pumped.

A 28-GHz Doherty Power Amplifier With a Compact Transformer-Based Quadrature Hybrid in 65-nm CMOS

This brief presents a single-ended, two-stage, and symmetric Doherty power amplifier (DPA). A rigorous and closed-form formula is proposed to design the transformer-based quadrature hybrid. The hybrid combines the advantages of flexibility, compactness, and low loss. A non-classic Doherty impedance inverting network is co-designed with the input network for phase matching. Besides, the parasitic parameters of the interconnects and RF pads are used to reduce the value of the inductor in the LC network. Designed and implemented in a 65-nm CMOS process, the fully integrated compact DPA prototype occupies only 0.35 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> active area. The experimental prototype operating at 28 GHz achieves 18.7 % power-added efficiency (PAE) at 6-dB power back-off (PBO). A maximum small-signal gain of 20.4 dB is achieved with a -3-dB bandwidth from 25.6 to 29.4 GHz. A 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 17.5 dBm is measured with the peak PAE of 27%. At 6-dB PBO, the DPA prototype increases the efficiency by 2.8 and 1.4 times over a normalized Class-B and Class-A PA, respectively.

A Highly Linear Dual-Stage Amplifier With Beyond 1.75-THz Gain–Bandwidth Product

This work reports a multipurpose highly linear ultrawideband amplifier with a gain-bandwidth product (GBP) of 1.75 THz, the highest reported in any monolithic microwave integrated circuit (MMIC) process. A transimpedance amplifier is cascaded with a distributed amplifier, emulating a receiver subsystem. Using a diamond heat spreader, to dissipate heat from transistors, the cascaded amplification subsystem can achieve very high output third-order-intercept point (OIP3) from 20 to 24 dBm when measured between 5 and 65 GHz. A small-signal average gain of 24 dB is observed over a frequency range exceeding the maximum measurable bandwidth from dc to 110 GHz. Compared with other ultrawideband MMIC amplifiers beyond 110-GHz bandwidth, the circuit offers a unique combination of high linearity (OIP3) and high gain. As a result, the cascaded amplifier is suitable for applications in optical-electrical converters, spectroscopy, and ultrawideband measurement systems in the subterahertz frequency range.

Bandwidth extension and conversion efficiency improvements beyond phase matching limitations using cavity-enhanced OPCPA.

The conversion efficiency and phase matching bandwidth of ultrafast optical parametric amplification (OPA) are constrained by the dispersion and nonlinear coefficient of the employed crystal as well as pulse shaping effects. In our work we show that an enhancement cavity resonant with the pump seeded at the full repetition rate of the pump laser can automatically reshape the small-signal gain in optical parametric chirped-pulse amplification (OPCPA) to achieve close-to-optimal operation. This new method termed cavity-enhanced OPCPA or C-OPCPA significantly increases both the gain bandwidth and the conversion efficiency, in addition to boosting gain for high-repetition-rate amplification. The goal in C-OPCPA is to arrive at a condition of impedance matching at all temporal coordinates, such that, in the absence of linear losses, all the incident pump power is dissipated in the nonlinear loss element, i.e., converted to signal and idler. The use of a low finesse enhancement cavity resonant with a low average power (<1W) and a high repetition rate (78MHz) pump source is shown to achieve more than 50% conversion efficiency into signal and idler from the coupled pump in an optical parametric process, whereas an equivalent amount of pump power in a single-pass configuration leads to negligible conversion. Additionally, the gain bandwidth is extended by a factor of 3-4 beyond the phase-matching limit. Our empirical observations are corroborated by a numerical analysis of depletion optimizing the single-pass case, which assesses the underlying impedance matching that is responsible for the observed performance improvements.

A 24–28-GHz Doherty Power Amplifier With 4-W Output Power and 32% PAE at 6-dB OPBO in 150-nm GaN Technology

A 24-28-GHz two-stage GaN Doherty power amplifier (PA) is designed and characterized. At millimeter-wave (mm-wave) frequencies, the low output impedance of the auxiliary transistor loads the Doherty combining network, which lowers the power added efficiency (PAE) in back-off. In this design, a small periphery auxiliary transistor is used to increase the output impedance of the auxiliary transistor. The periphery ratio of the auxiliary and the main transistors is 77%. Even though, compared to symmetric Doherty PAs, the load modulation of the main transistor is reduced, this amplifier still achieves 32% and 23% PAE at 6 and 9-dB output power back-off, respectively. Attributing to the small auxiliary transistor, the amplifier obtains a small signal gain of 19 dB. The maximum output power of the amplifier is 4 W with a peak PAE of 42%.

A Ka-Band Switchable LNA With 2.4-dB NF Employing a Varactor-Based Tunable Network

This letter presents a multiband switchable low-noise amplifier (LNA) in the 0.1- μm GaAs pHEMT process. Employing a new varactor-based tunable network as the interstage matching circuit, the operation bands can be tuned consecutively and cover the 5G millimeter-wave frequency bands N257/N260. The proposed tunable structure functions well without sacrificing noise performance or increasing dc consumption and chip area. In the entire operation band from 26.5 to 41 GHz, the LNA achieves a small-signal gain of over 24 dB and a noise figure (NF) of less than 2.9 dB. The measured result shows a small-signal gain of 25.1 dB/27.7 dB and an NF of 2.4 dB/2.8 dB at 28 GHz/39 GHz. The measured input 1-dB compression point (IP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1dB</sub> ) is -18.3 dBm/-17 dBm at 28 GHz/39 GHz. The measured input-referred intercept point (IIP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) is -8.8 dBm/-8.5 dBm at 28 GHz/39 GHz. The LNA has a chip size of 1.6 mm ×1 mm, and the total power consumption is 74 mW. To the best of our knowledge, the proposed LNA is the state-of-the-art Ka-band switchable LNA and has similar performance compared with single-band LNAs using the same technology.

AlGaN/GaN-Based Laterally Gated High-Electron-Mobility Transistors With Optimized Linearity

In this work, highly linear AlGaN/GaN laterally gated (or buried gate) high-electron-mobility transistors (HEMTs) are reported. The effect of gate dimensions on source-access resistance and the linearity of laterally gated devices are investigated experimentally in detail for the first time. Transistors with different gate dimensions and conventional planar devices are fabricated using two-step electron beam lithography (EBL). Current–voltage, source-access resistance, small-signal, and two-tone measurements are performed to evaluate the linearity of devices. Contrary to conventional planar HEMTs, the intrinsic transconductance of laterally gated devices monotonically increases with increasing gate voltage, showing a similar behavior as junction field-effect transistors (FETs). The source-access resistance shows a polynomial increase with the drain current, which can be reduced by decreasing the filling ratio of the buried gates. Through the optimization of these two competing factors, i.e., intrinsic transconductance and the source-access resistance, flat transconductance with high linearity is achieved experimentally. The laterally gated structure shows flat transconductance and small-signal power gain over a larger span of gate voltage that is 2.5 times higher than a planar device. Moreover, 6.9-dB improvement in output intercept point (OIP3)/ ${P}_{\text {DC}}$ is achieved. This approach can be used to improve the linearity of AlGaN/GaN HEMTs at the device level.

GaN МИС малошумящего усилителя Х-диапазона

The purpose of this paper is to design a microwave monolithic integrated circuit (MMIC) for low noise amplifier (LNA) X-band (7-12 GHz) based on technology of gallium nitride (GaN) high electron mobility transistor (HEMT) with a T-gate, which has 100 nm width, on a silicon (Si) semi-insulating substrate of the OMMIC company. The amplifier is based on common-source transistors with series feedback, which was formed by high-impedance transmission line, and with parallel feedback to match noise figure and power gain. The key characteristics of an LNA are noise figure and gain. However, in this paper, it was decided to design the LNA, which should have a good margin in terms of input and output power. As a result, GaN technology was chosen, which has a higher noise figure compared to other technologies, but eliminates the need for an input power limiter, which in turn significantly increases the overall noise figure. As a result LNA MMIC was developed with the following characteristics: noise figure less than 1.6 dB, small-signal gain more than 20 dB, return loss better than -13 dB and output power more than 19 dBm with 1 dB compression in the range from 7 to 12 GHz in dimensions 2x1.5 mm², which has a supply voltage of 8 V and a current consumption of less than 70 mA. However, it should be said that LNA was only modeled in the AWR DE.

A Broadband Asymmetrical GaN MMIC Doherty Power Amplifier with Compact Size for 5G Communications

This paper proposes a broadband asymmetrical monolithic microwave integrated circuit (MMIC) Doherty power amplifier (DPA) using 0.25-μm gallium-nitride process with a compact chip size of 2.37 × 1.86 mm2 for 5G communication. It adopts an unequal Wilkinson’s power divider with a ratio of 2.5:1, where 71.5% of the total power is transferred to the main amplifier for higher gain. Different input matching networks are used to offset phase difference while completing impedance conversion. This design also applies a novel topology to solve the problem of large impedance transformer ratio (ITR) in conventional DPA, and it optimizes the ITR from 4:1 to 2:1 for wider band. Moreover, most of the components of the DPA including power divider and matching networks use lumped inductors and capacitors instead of long transmission line (TL) for a smaller space area. The whole circuit is designed and simulated using Agilent’s advanced design system (ADS). The simulated small-signal gain of DPA is 8–11 dB and the saturation output power is more than 39.5 dBm with 800 MHz band from 4.5 GHz to 5.3 GHz. At 6-dB output power back-off, the DPA demonstrates 38–41.3% power added efficiency (PAE), whereas 44–54% PAE is achieved at saturation power.

A 24-29.5 GHz Voltage-Combined Doherty Power Amplifier Based on Compact Low-Loss Combiner

In this brief, a 24-29.5 GHz millimeter-wave (mm-wave) voltage-combined Doherty power amplifier (DPA) based on compact low-loss combiner is proposed for the fifth-generation (5G) applications. By maximizing the use of parasitic parameters in the circuit, a compact low-loss combiner is proposed to achieve the required impedance transformation with only one additional series capacitor. A detailed design procedure is also introduced in the brief. Based on the proposed combiner, a fully integrated Doherty PA is implemented in 0.13- μm SiGe BiCMOS process with a core area of only 0.29 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The DPA achieves a 27% -3-dB small-signal gain fractional bandwidth and a 15.9 dB small signal gain at the center frequency of 27 GHz. The -1-dB Psat bandwidth covers 24-29.5 GHz (20% fractional bandwidth), and the maximum output power is 20.8 dBm ± 0.4 dB. From 24 to 29.5 GHz, the designed DPA provides 23.2% to 28.4% power-added efficiency (PAE) at saturated output power, and 18.3% to 21.9% PAE at 6 dB of output power back-off (OPBO).

Three-Terminal Floating-Gate Cell for Threshold-Voltage Control of Organic Thin-Film Transistors

A floating-gate (FG) cell as a circuit-level approach to control the threshold voltage of organic thin-film transistors (TFTs) operated in the transdiode configuration is presented. Charging and discharging of the FG are achieved by controlling the charge leakage through the gate dielectric of one of the organic TFTs that constitute the FG cell. Using programming voltages not exceeding 4 V, systematic tuning of the threshold voltage to values between −0.5 and 2.6 V was achieved. The versatility of the concept is demonstrated by employing organic-TFT-based FG cells as transdiodes with programmable threshold voltage in passive rectifiers and diode-load inverters fabricated on flexible, transparent plastic substrates. Rectifiers with programmable FG cells show flatter frequency response, improved 3-dB point, and reduced ripple compared to conventional rectifiers. Inverters with programmable FG-transdiode load have larger small-signal gain, larger output-voltage swing, and larger noise margins than conventional diode-load inverters.