Third-order Intermodulation Distortion Research Articles

Improvement of Linearity and Mitigation of Dispersion-Induced Power Fading in Multi-Channel Phase-Modulated Analog Photonic Link Based on a Polarization Modulator

We propose a multi-channel phase-modulated analog photonic link (APL) with linearization and mitigation of dispersion-induced power fading based on a polarization modulator (PolM). When the modulated signal from the PolM goes through a polarization controller and a polarization beam splitter (PBS), the odd- and even-sidebands of the phase-modulated signal can be separated into orthogonal polarization states and travel out from the two outputs of the PBS. By introducing a proper phase shift between two orthogonal polarization states, the third-order intermodulation distortion can be suppressed while the dispersion-induced power fading can be mitigated with different working frequency of the APL and different transmission length of the subchannel. Both theoretical analysis and experimental verification are given. Experimental results show the spurious free dynamic range of above 96 dB·Hz2/3 at the noise floor of –143 dBm/Hz, which is improved by 10.2 dB as compared with conventional phase-modulated APL.

Impact of interface trap charges on dopingless tunnel FET for enhancement of linearity characteristics

For the first time, we have explored the effect of positive and negative interface trap charges on the dopingless device using charge plasma concept and named the proposed device as heterogeneous gate dielectric charge plasma tunnel field-effect transistor (HD-CP-TFET). The heterogeneous gate dielectric is considered to improve the ON-state current and device performance. The main intention of this work is to improve the drain current, transconductance characteristics along with linearity figure-of-merits (FOMs). A comparative analysis is done with conventional CP-TFET in the presence of interface trap charges (ITCs). From comparative results, it is found that the proposed device shows a better performance in the presence of interface trap charges. All the simulations are performed on ATLAS TCAD device simulator. The results show that the proposed device has a better tunneling current, transconductance (\(g_{\text {m}}\)), cut-off frequency (\(f_{\text {T}}\)), second-order voltage intercept point (VIP2), third-order voltage intercept point (VIP3), third-order input intercept point (IIP3), and third-order intermodulation distortion (IMD3). Thus, the proposed device (HD-CP-TFET) shows the better performance in the presence of interface trap charges and indicates that this device is suitable for low-voltage analog/RF applications.

Improvement of Carrier Power to Third-Order Intermodulation Distortion Power Ratio for a Power Amplifier at 5.25 GHz using LINC Method

Introduction:This paper focuses on improving the power amplifier linearity for wireless communications. The use of a single branch of a power amplifier can produce high distortion with low efficiency.Method:In this paper, the Linear Amplification with Nonlinear Components (LINC) technique is used to improve the linearity and efficiency of the power amplifier. The LINC technique is based on converting the envelope modulation signal into two constant envelope phase-modulated baseband signals. After amplification and combining the resulting signals, the required linear output signal is obtained. To validate the proposed approach, LINC technique is used for linearizing an amplifier based on a GaAs MESFET (described by an artificial neural network Model).Conclusion:Good results have been achieved, and an improvement of about 40.80 dBc and 47.50 dBc respectively is obtained for the Δlower C/I and Δupper C/I at 5.25 GHz.

Linearity Comparison of Silicon Carrier-Depletion-Based Single, Dual-Parallel, and Dual-Series Mach–Zehnder Modulators

In this paper, a model is built to investigate the linearity of silicon carrier depletion based Mach–Zehnder modulators (MZMs). By approximating the nonlinear electro-optical response of a PN junction with a fourth-order polynomial, the model quantitatively calculates the modulation linearity of three different MZM configurations that have been widely used in analog optical links, i.e., single, dual-parallel, and dual-series MZMs, and qualitatively explains their respective operation mechanisms to suppress the third-order intermodulation distortion. The optimal operation condition of each configuration is derived to enhance the first-order harmonic component and suppress the nonlinear distortion. A fair comparison is performed between the three configurations in terms of their robustness, footprint, strength of the first-order harmonic component, stability, and tolerance against variations of driving RF power and control error, and so on. The result indicates that the dual-series MZM represents a reasonable tradeoff between these performance characteristics of interests.

The effects of the peaking currents on the performance of the Doherty power amplifier: an analytical and experimental study

Recognizing that the ratio of the peaking and main amplifier transconductances is a crucial parameter in the design of Doherty power amplifiers, we propose an analytical method to specify the optimum value of this ratio. The method is validated both through simulations based on circuit-level model of the Doherty power amplifier and the experiments using a 100 W dual driven symmetrical LDMOS Doherty power amplifier manufactured. According to the experiments, overdriven peaking amplifier is resulting in lower drain voltage at the main side, hence causing low power efficiency. Conversely, underdriven peaking amplifier is saturating the main amplifier, which in turn results in decreased linearity. Both simulation and experimental results clearly revealed that the amplifier efficiency and linearity strongly depend on the drive levels of the main and peaking amplifiers. The third-order intermodulation distortion of a 44 dBm and 2.655 GHz Doherty power amplifier which is measured as − 29.75 dBc in the overdriven case, is increased up to − 19.40 dBc in the underdriven case. However, the drain efficiency which is measured at 47.84% in the overdriven case is improved to 54.36% when the peaking amplifier is operated in the underdriven mode for 47 dBm and 2.655 GHz.

Investigation on Third-Order Intermodulation Distortions Due to Material Nonlinearities in TC-SAW Devices.

Nonlinearity can give rise to intermodulation distortions in surface acoustic wave (SAW) devices operating at high input power levels. To understand such undesired effects, a finite element method (FEM) simulation model in combination with a perturbation theory is applied to find out the role of different materials and higher order nonlinear tensor data for the nonlinearities in such acoustic devices. At high power, the SAW devices containing metal, piezoelectric substrate, and temperature compensating (TC) layers are subject to complicated geometrical, material, and other nonlinearities. In this paper, third-order nonlinearities in TC-SAW devices are investigated. The materials used are LiNbO3-rot128YX as the substrate and copper electrodes covered with a SiO2 film as the TC layer. An effective nonlinearity constant for a given system is determined by comparison of nonlinear P-matrix simulations to third-order intermodulation measurements of test filters in a first step. By employing these constants from different systems, i.e., different metallization ratios, in nonlinear periodic P-matrix simulations, a direct comparison to nonlinear periodic FEM-simulations yields scaling factors for the materials used. Thus, the contribution of the different materials to the nonlinear behavior of TC-SAW devices is obtained and the role of metal electrodes, substrate, and TC film are discussed in detail.

Volterra Series Based Linearity Analysis of a Phase-Modulated Microwave Photonic Link

An analytical technique based on Volterra series for systematically computing distortion in analog microwave photonic (MWP) links is presented in this paper. In the analysis, we express both modulator and photodetector responses in the MWP link as Taylor series expansions, which are then nested to give rise to Volterra series for systems with memory. Closed-form expressions of the link photocurrent and optical power based on the nth-order Volterra kernels are derived from the functional Taylor series of the MWP link. These expressions are applicable in both direct detection and phase-modulated conditions hitherto referred to as memoryless case and with memory, respectively. The synthesized Volterra kernels are primarily used to determine key figures of merit such as nth-order harmonic distortion, third-order intermodulation distortion (IMDn), and third-order intercept point (OIPn) for an arbitrary MWP link. We apply the technique to a photonic link having a ring-assisted Mach-Zehnder interferometer (RAMZI) filter and compare its OIP3 performance with that of an MZI discriminator. Within a bandwidth of 20 GHz, it is shown that RAMZI has 10-dB better OIP3 performance than MZI. We also illustrate that OIP3 and IMD measurements done using three-tone tests would result in more accurate predictions of MWP link parameters than standard two-tone tests.

A novel scheme to suppress the third-order intermodulation distortion based on dual-parallel Mach–Zehnder modulator

A scheme to enlarge the spurious free dynamic range (SFDR) of the microwave photonic link is proposed based on a dual-parallel Mach–Zehnder modulator (DPMZM). By properly adjusting the phase of the RF signals and the bias voltages of the DPMZM, the second-order spurious components in the optical carrier band (OCB) of the two sub-MZMs can be canceled out completely, and the third-order and fifth-order spurious components in the first-order upper sideband (1-USB) produced by one sub-MZM have equal amplitude but $$180{^{\circ }}$$ phase difference with the other sub-MZM. Therefore, as the two optical beams are combined at the output of the DPMZM and the OCB and the 1-USB are abstracted by a bandpass filter to generate the transmitted signal, all the major optical spurious components that contribute to the third-order intermodulation distortion (IMD3) are canceled out. Theoretical analysis and simulation results show that the proposed scheme, without digital linearization and other optical processor, can suppress IMD3 approximately 30 dB and improve the SFDR by $$18~\hbox {dB}\,\hbox {Hz}^{2/3}$$ compared with the conventional quadrature biased MZM system.

Hybrid Linearization of Broadband Radio-Over-Fiber Transmission

This letter presents analog and digital pre-distortion hybrid linearization of a broadband radio-over-fiber transmission system. Analog pre-distortion (APD) is used to mainly compensate for out-of-band nonlinear distortion, and digital pre-distortion (DPD) is used to mainly compensate for in-band nonlinear distortion and memory effect. Thus, by combining APD and DPD, all the quiescent distortions and memory effect can be suppressed effectively. The hybrid APD and DPD linearization is evaluated in three different scenarios: two 20-MHz long-term evolution (LTE) signals located at 800 and 900 MHz, and located at 800 and 840 MHz, and three 20-MHz LTE signals located at 800, 850, and 900 MHz. All three experiments show that the hybrid linearization results in better improvement in error vector magnitude, adjacent-channel power ratio, and third-order intermodulation distortion than the APD-only and DPD-only.

Photonic receiving and linearization of RF signals with improved spurious free dynamic range

A linearization scheme for receiving broadband radio frequency (RF) is theoretically analyzed and experimentally demonstrated. The system uses three intensity modulators (IMs) to impose a two-tone RF signal on an optical carrier. We demonstrate that the linearization technique can be used to suppress the third-order inter-modulation distortion (IMD3) and the five-order inter-modulation distortion (IMD5) components simultaneously. An improvement of the spurious free dynamic range (SFDR) as large as 112.13 dB in 1-Hz bandwidth is achieved, which is 13.5 dB higher than the SFDR of a conventional intensity-modulated scheme.

Wideband high-efficiency linearized PA design with reduction in memory effects and IMD3

ABSTRACTAn analytical method is proposed to reduce the memory effects and third-order intermodulation distortions for improving the linearity of wideband power amplifier (PA). An excellent linearity can be obtained by reducing the second-harmonic output power levels and reducing the envelope voltage components in the megahertz range. An improved wideband Chebyshev low-pass matching network including the bias network is analyzed and designed to validate the proposed method. The measured results indicate that a wideband high-efficiency linearized PA is realized from 1.35 to 2.45 GHz (fractional bandwidth = 58%) with power added efficiency of 60–78%, power gain of 10.8–12.3 dB, and output power of 40.0–41.2 dBm. For a 20 MHz LTE modulated signal, the adjacent channel leakage ratios (ACLRs) of the proposed PA with digital pre-distortion (DPD) linearization are −55.7 ~ −53.9 dBc across 1.5–2.4 GHz at an average output power of 32.4–33.6 dBm. For a 40 MHz two-carrier LTE modulated signal, the ACLRs of the proposed PA with DPD linearization are −51.1 ~ −48.2 dBc at an average output power of ~30.5 dBm in the frequency range from 1.5 GHz to 2.4 GHz.

Dual-wavelength linearization of analog photonic link based on PM–IM conversion

A novel method for linearization of phase-modulated analog photonic link is proposed in this paper. Heterodyne carrier source (HCS) is obtained by polarization multiplexing of two different-wavelength optical carriers. A Z-cut phase modulator (PM) which exhibits different electro-optic modulation indexes in orthogonal polarization states is used to modulate radio frequency signal onto the heterodyne optical carriers. Two channels of a WDM are used to filter out the positive or negative optical sidebands respectively and thus implement PM–IM conversion. The third-order intermodulation distortions (IMD3s) of the two different WDM channels are opposite in phase. IMD3 can be suppressed by combining signals from the two different WDM channels and adjusting the power ratio of the two optical carriers. Apart from the obvious improvement of SFDR, no need for bias control and easy adjusting of the power ratio make the method easy to implement. Experimental results show that the spurious free dynamic range (SFDR) of the system is improved by 14.54 dB.

Asymmetrical Doherty power amplifier using ferroelectric ceramics for linearity enhancement

ABSTRACTA new asymmetrical Doherty power amplifier (DPA), using ferroelectric ceramics, is proposed for linearity improvement. The uneven power divider based on ferroelectric ceramics substituted for the conventional Wilkinson power divider, the uneven power divider ratio between main amplifier and peak amplifier is performed by the proposed structure, at the same time, because of the loaded ferroelectric ceramics based on Barium Strontium Titanate (BST), the phase differences between outputs of proposed divider is changed to desired by modifying the voltage of BST. Furthermore, at high power lever, the phase of peak amplifier can be modified to cancel distortion of main amplifier, so the AM-PM distortion of total DPA can be corrected by tuning voltage of BST. Compared to a conventional DPA, the third-order inter-modulation distortion of proposed DPA is reduced by 18 dB, at the same time, the PAE is also improved about 6–7%.

A GaN HEMT Global Large-Signal Model Including Charge Trapping for Multibias Operation

This paper presents a novel empirical model for gallium nitride on silicon carbide high-electron mobility transistors. A global state-space formulation describes charge trapping effects by means of suitable 2-D nonlinear lag functions of the applied voltages, extracted from a reduced set of double-pulse current-voltage characteristics. The implementation in CAD tools involves a simple equivalent circuit and lookup tables, making the model well suited for power amplifier design in the presence of signals of practical interest. An extensive validation at both low (4 MHz) and radio frequencies (5.5 GHz) exhibits good accuracy and a robust performance prediction for the operation above the cut-off of dispersive phenomena, across different operating classes and loads, in terms of output power, power-added efficiency, and third-order intermodulation distortion. These results show that traps with both linear and nonlinear dynamics are stimulated in large-signal operation, and that these must be taken into account for global model predictions.

An Optimized Segmented Quasi-Memoryless Nonlinear Behavioral Modeling Approach for RF Power Amplifiers

This paper presents an optimized segmented modeling approach using a new quasi-memoryless (QM) behavioral model (BM) that allows for RF power amplifier (RF PA) modeling over a range of different solid state PA technologies. The presented model is a combination of an existing semiphysical amplitude-modulation-to-amplitude-modulation (AM/AM) memoryless BM, which correctly predicts third-order intermodulation distortion (3rd IMD) response in the small signal region, with the newly proposed amplitude-modulation-to-phase-modulation (AM/PM) model derived from the existing AM/AM model. Using the segmentation and optimization methods, performance comparisons with this new model are presented, showing normalized mean squared error AM/PM improvements up to 20 dB, as well as over 5-dB improvement in predicting the 3rd IMD using the proposed model. Comparisons against other well-known QM BMs are conducted using measured data as well as with data presented in the literature. The effects of these improvements on linearizer performance are also evaluated. The model significantly improves system-level modeling by allowing designers to accurately predict system performance using various RF PA devices over a range of technologies, based on data available through manufacturers’ data or simple tests.

Multi-octave analog photonic link with improved second- and third-order SFDRs

The second- and third-order spurious free dynamic ranges (SFDRs) are two key performance indicators for a multi-octave analogy photonic link (APL). The linearization methods for either second- or third-order intermodulation distortion (IMD2 or IMD3) have been intensively studied, but the simultaneous suppression for the both were merely reported. In this paper, we propose an APL with improved second- and third-order SFDRs for multi-octave applications based on two parallel DPMZM-based sub-APLs. The IMD3 in each sub-APL is suppressed by properly biasing the DPMZM, and the IMD2 is suppressed by balanced detecting the two sub-APLs. The experiment demonstrates significant suppression ratios for both the IMD2 and IMD3 after linearization in the proposed link, and the measured second- and third-order SFDRs with the operating frequency from 6 to 40 GHz are above 91dB⋅Hz1∕2 and 116dB⋅Hz2∕3, respectively.

Experimental demonstration of a hybrid integrated dual-parallel modulated DFB semiconductor laser with suppressed nonlinear distortions

A hybrid integrated dual-parallel modulated DFB laser is experimentally demonstrated. Utilizing the proposed method, the nonlinear distortions of the DFB laser, including the second harmonic distortion (2HD) and the third-order intermodulation distortion are suppressed significantly. Comparing with the single modulated DFB laser, the 2HD is reduced by 8.6 dB and the spurious free dynamic range is increased from 87.2 dB·Hz2/3 to 90.3 dB·Hz2/3.

A Novel Pre-Distortion Circuit of Lasers Fabricated in 0.18- $\mu \text{m}$ CMOS Technology

A novel CMOS analogue broadband pre-distortion circuit fabricated in a 0.18- $\mu \text{m}$ CMOS technology is presented in this letter. The pre-distortion circuit consists of a common-gate amplifier and a gain-booting amplifier. The pre-distortion signal can be adjusted by changing the biased voltage of the transistor. Without phase shifters, time delay lines and VGAs, the circuit can be easily implemented for its simple structure. The chip area is $0.58\times 0.47$ mm 2 including all the pads, and it consumes 7.74 mW with 1.8-V supply voltage. In the RoF system, the measured results show that the third-order inter-modulation distortion has a significant reduction of 16 dBc at 1.8-GHz frequency when the pre-distortion circuit is used.

A CMOS Antiphase Power Amplifier With an MGTR Technique for Mobile Applications

In this paper, a CMOS antiphase power amplifier (PA) is presented with a multigate transistor (MGTR) technique that improves its linearity. The drive stage of the PA is biased in the subthreshold region, such as in class C, to realize the antiphase technique. The nonlinearity of the power stage of the PA is canceled out using the third-order intermodulation distortion and phase distortion of the drive stage. The cancellation effect is further optimized and enhanced without any performance degradation with the aid of the proposed MGTR technique at the drive stage. Unlike the traditional technique, which suppresses the nonlinearity of the PA, the MGTR technique is used to enhance the nonlinearity of the drive stage to cancel out the significant nonlinearity of the power stage. The proposed PA is fabricated with a 180-nm RF CMOS process and used to verify the linearity by WCDMA and LTE signals. The measurement results show an average output power of 25.8 dBm, PAE of 28%, and error vector magnitude of 3% at 1.85 GHz for the WCDMA. The PA also shows an average output power of 24.4–25.8 dBm at 1.7–2.0 GHz for the WCDMA. The PA is verified for LTE signals with 10 MHz of bandwidth/16 QAM and with 20 MHz of bandwidth/64 QAM. No digital predistortion or off-chip components are utilized.

A High-Frequency Compact Model for Graphene Resonant Channel Transistors Including Mechanical Nonlinear Effects

This paper presents a physical-based high-frequency nonlinear model of graphene resonant channel transistors (G-RCTs), including a nonlinear electromechanical model of doubled clamped graphene mechanical resonators. To accurately describe the temperature-dependent modal dispersion, both bias- and temperature-dependent effects are considered. The temperature-dependent built-in strain, the bias-based electrostatic force, and the spring restoring force, including the nonlinear term upon deformation, are used to describe the mechanical motion of the suspended beam. The nonlinear model is validated by the measured results of G-RCTs, which indicate that our model can predict the experimental results well. Moreover, the nonlinear effects, including harmonic distortion, third-order intermodulation distortion, and the hysteresis and nonlinear behavior of G-RCTs, are also studied. The results show that the nonlinear physical model can predict the response of G-RCTs very well. These results also show that the mechanical nonlinearity has strong effects on nonlinear distortion for G-RCTs. The nonlinear equivalent circuit model could be useful for nanoelectromechanical system in the applications of high-frequency integrated circuits.