Third-order Intermodulation Distortion Component Research Articles

Linearized microwave downconversion link based on fast and intelligent impairment equalization for noncooperative systems

We experimentally demonstrated the use of intelligent impairment equalization (IIE) for microwave downconversion link linearization in noncooperative systems. Such an equalizer is realized based on an artificial neural network (ANN). Once the training process is completed, the inverse link transfer function can be determined. With the inverse transformation for the detected signal after transmission, the third-order intermodulation distortion components are suppressed significantly without requiring any prior information from an input RF signal. Furthermore, fast training speed is achieved, since the configuration of ANN-based equalizer is simple. Experimental results show that the spurious-free dynamic range of the proposed link is improved to 106.5 dB · Hz2/3, which is 11.3 dB higher than that of a link without IIE. Meanwhile, the training epochs reduce to only five, which has the potential to meet the practical engineering requirement.

High-performance dual-band radio-over-fiber link for future 5G radio access applications

For the fronthaul between the baseband unit and the remote radio unit (RRU), radio over fiber (RoF) is promising to replace the Common Public Radio Interface in beyond fifth-generation and the sixth-generation wireless communication systems. The weight, size, and power consumption of the RRU can be greatly reduced, along with easy support for the millimeter-wave band. In this paper, a dual-band RoF link is proposed, where flexible switching between high-frequency (28 GHz) and low-frequency (3.5 GHz) RF channels is realized through polarization control. Single-sideband modulation is performed on 28 GHz signals to avoid periodic power fading during long-distance fiber transmission. By adjusting the DC bias, the third-order intermodulation distortion component in the 3.5 GHz signal is suppressed, and the spur-free dynamic range (SFDR) is improved. Experimental results show a channel isolation of above 43 dB. The link gain of the 28 GHz signal channel is flat, and the SFDR of the 3.5 GHz signal channel can reach 118.6 d B ⋅ H z 4 / 5 . In the case of RF vector signal transmission, the adjacent channel power ratio of the 3.5 GHz signal channel is optimally up to 48 dB, and the error vector magnitude is 2.9%.

Third-order intercepts and nonlinear distortion level investigation for pre and post multilayer pHEMTs

Investigation of the third-order intercept point, IP3 and nonlinear distortion level, NDL for pre-and post-multilayer processed GaAs pHEMTs has been accomplished by employing two-tone intermodulation distortion measurements. The third-order intercept point is a biasing, input power, frequency-dependent term, particularly related to the fundamental and third-order intermodulation distortion component and the study extended from low to high temperatures. The main findings are that the output referenced OIP3 decreased while the input referenced IIP3 increased with frequency at peak transconductance condition and the study further extended to multi-bias operation condition. Within the measured temperature range, the IP3 and NDL modified significantly following the behaviour of IMD3 distortion. This investigation of IP3 is utilized to measure how much distortion is created and referring this to the antenna input gives a straightforward strategy to decide whether or not the spec can be met. On the other hand, analysis of NDL is vital for choosing the most excellent biasing alternative with the entryway measurements of the device to create a compromise agreeing to the desired utilization.

Distortion Mitigation in Multiband OFDM RoF Transmission Employing Blind Post Equalizer

We propose and experimentally demonstrate a blind adaptive equalizer for a multiband (MB) orthogonal frequency-division multiplexing (OFDM) radio-over-fiber (RoF) system. The proposed equalizer adaptively decreases nonlinear and linear distortion, which might lead to serious signal degradation in MB OFDM transmission, without the use of a training signal. Instead of a training signal, error vector magnitude (EVM) and the power difference between the signal and the third-order intermodulation distortion components were observed in the equalizer. Therefore, the performance enhancement of MB OFDM transmission was experimentally verified in terms of EVM from 5.52% to 2.75% by mitigation of distortion. Consequently, the dynamic range of radio frequency input power was improved when the proposed equalizer was employed in an MB OFDM RoF system without increasing system overhead.

Designing Linear PAs at Millimeter-Wave Frequencies Using Volterra Series Analysis

Power amplifiers (PAs) at millimeter-wave (mm-wave) frequencies are required for delivering high output linear power while being efficient; however, their performance is severely affected by the scaled semiconductor technology and the operating frequency. To improve the linearity of mm-wave PAs, it is recommended that an external linearization technique such as predistortion be used. The PA presented in this paper uses adaptive predistortion (APD). The APD linearization technique was developed using the Volterra series analysis on the silicon–germanium (SiGe) heterojunction bipolar transistor. The Volterra series analysis was used to identify and characterize the third-order intermodulation distortion components. The PA uses a single-ended common-emitter topology. It consists of three stages biased in the Class AB mode. The PA and APD were designed using the 130-nm SiGe bipolar and complementary metal–oxide–semiconductor process. The PA and APD achieve an optimum third-order intermodulation reduction of 10 dB and an improved linear output power of 2.5 dBm.

Bit Error Probability in the Presence of Third-Order Intermodulation Distortion Component from Power Amplifier of Different Mobile Systems

This paper presents an evaluation of the bit error probability in the presence of the third-order intermodulation distortion (IMD) component generated by power amplifiers for the purpose of investigating the interference among different mobile systems. This paper derives a probability density function (PDF) for the third-order IMD component since the derivation of the bit error probability in the presence of the third-order IMD component requires the PDF of the third-order IMD component. This paper concludes that the PDF of the third-order IMD component has different stochastic properties from those of thermal noise. The PDF of the third-order IMD component should be taken into account as well as that of thermal noise when deriving the bit error probability in the presence of the third-order IMD component.

Power Supply Noise in Analog Audio Class D Amplifiers

A potential drawback of class D amplifiers (CDAs) is their relatively poor tolerance to power supply noise. It has been recently established by means of a linear model that the manifested nonlinearities due to the supply noise are the fundamental noise frequency component and second-order intermodulation components, qualified by the power supply rejection ratio (PSRR) and intermodulation distortion (IMD), respectively. In this paper, multidimensional Fourier series analysis is applied to open-loop, single-, and double-feedback pulsewidth modulation CDAs, and expressions for PSRR, IMD, and fold-back distortion (FBD) are derived. This analysis takes into account the nonlinear pulse modulation process (unaccounted for in the linear model), and all components of PSRR and IMD nonlinearities are hence modeled. It is shown that the first-harmonic PSRR and third-order IMD components, which are usually ignored in CDAs and linear amplifiers, are significant and that, under certain conditions, the third-order IMD components can be higher than the second-order IMD components. It is also shown that the loop gain should be high for high PSRR and low IMD. Furthermore, significant FBD can arise due to the intermodulation between the supply noise, the input signal, and the carrier, and interestingly, the FBD in closed-loop CDAs is more serious than that in open-loop CDAs. The analyses herein are verified by computer simulations and on the basis of measurements on a prototype CDA IC and on other hardware realizations.