Frequency domain model fitting and Volterra analysis implemented on top of harmonic balance simulation

Abstract The modern wireless communication techniques are aiming on increasing bandwidth and the number of carriers for higher data rate. This sets challenging linearity requirements for RF power amplifiers (PAs). Unfortunately, high linearity can only be obtained at the cost of efficiency. In order to improve the performance of the PA, in-depth understanding of nonlinear behaviour is mandatory. This calls for techniques that can give componentwise information of the causes of the distortion. The aim of this thesis is to develop a technique that can provide such information. This thesis proposes a detailed distortion analysis technique that is based on frequency domain fitting of polynomial models. Simulated large-signal spectra are used for fitting as these contain the necessary information about the large-signal bias point and amplitude range. Moreover, in the frequency domain the delays are easy to compensate, and detailed analysis to any fitted tone can be performed. The fitting procedure as such is simple but becomes difficult in multi-dimensional nonlinearities if the controlling voltages correlate strongly. In this thesis the solvability and reliability of the fitting procedure is increased by numerical operations, model-degree reduction and by using different excitations. A simplified Volterra method is used to calculate the distortion contributions by using the fitted model. The overall distortion is analysed by calculating the voltage response of the contributions of each nonlinearity to the terminal nodes of the device by the use of linear transfer functions of the circuit. The componentwise analysis is performed by phasor presentation enabling the cancelling mechanisms to be seen. The proposed technique is implemented on top of harmonic balance simulation in an APLAC circuit simulator in which extensive distortion simulations are performed. The technique relies on the existing device model and thus the fitted model can be only as accurate as the particular simulation model. However, two different RF PAs are analysed that show a good agreement between measurements and simulations. The proposed technique is verified with several test cases including amplitude dependent amplitude and phase distortion, intermodulation distortion sweet spots, bandwidth dependent memory effects and impedance optimization. The main finding of the detailed analysis is that the distortion is a result of several cancelling mechanisms. In general, cubic nonlinearity of transconductance is dominating the in-band distortion but is cancelled by the 2nd-degree nonlinearity that is mixed to the fundamental band from envelope and 2nd harmonic bands that is usually the main cause of memory effects

Building lumped models for measured passive mm-wave components

Abstract This paper presents a synthesis flow for building lumped circuit models of arbitrary complexity for mm-wave IC passive components, based on S-parameters obtained by measurements or electromagnetic (EM) field simulations. Lumped circuit models are needed in time-domain simulations, or to speed up the fine-tuning of passive circuit blocks, as iterating is much faster in circuit simulators than in EM simulator. Modeling algorithm is implemented in MATLAB, and the design flow has a few new features. The device model is given by Spice netlist, and its structure or complexity is not limited. Differential and common mode forms of admittance parameters are used to simplify solving the initial model component values that are then refined manually or by numerical optimization. The flow is illustrated by modeling a parallel LC resonator, whose response has been measured from 1 to 40 GH

On the microwave photonics based pulsed-time-of-flight techniques in the measurement of the thickness of dielectric sheets

Abstract This paper proposes a time domain measurement technique for characterizing the thickness of dielectric material based on pulse-domain microwave photonics and pulsed time-of-flight configuration. Short laser pulses from a semiconductor laser diode are converted to electrical pulses using a wideband photodetector. These pulses are fed to an antenna, providing a simple and accurate non-destructive measurement technique for material characterization. The thickness of the sample is calculated based on the propagation delay of a radio wave by measuring the transit time of a short electromagnetic pulse. The propagation delay is determined from the front edge of the energy envelope. Results show that the measured propagation delay is linearly dependent on the sample thickness. The technique achieves a measurement precision in the sub-mm range with a measurement time of 40ms

Study of transmitter interference to receiver at 2 GHz with high antenna port isolation

Abstract The paper presents simulated and measurement results of a planar antenna structure at 2 GHz center frequency. The antenna has two ports implemented into the same conductive body. The antenna shows measured -10 dB impedance bandwidth from 1.87 GHz to 2.18 GHz with average 41.3 dB isolation between the antenna ports over the studied frequency bandwidth. Antenna is used to measure transmitted WCDMA FDD signal leakage to the receiver with a presence of blocker signal, which is transmitted over the air. The system measurements show that the RF filtering requirements can be relaxed based on 3GPP standard by using highly isolated antenna structure. Application areas can be found at the both ends of the mobile communications system, mobile devices and small cell base stations

Performance improvement of multi-stacked CMOS mm-wave power amplifiers based on negative capacitance phase compensation

Abstract This paper proposes a method for performance improvement of multi-stacked CMOS millimeter-wave power amplifiers based on negative capacitance phase detuning, which can be generalized to other phase detuning techniques. It not only yields better inter-stage matching between stacks, but also offers the advantage of relaxed inter-stage phase rotation due to transistor parasitics. A x1.6 output power/gain and 7% efficiency improvement is observed as a result of the proposed technique. This is achieved because phase misalignment between stacks is minimized. The method is evaluated using simulations based on 28GHz PA in 45nm CMOS technology

Design of stacked-MOS transistor mm-wave class C amplifiers for Doherty power amplifiers

Abstract This paper discusses the design requirements of class C auxiliary (aux) amplifiers deployed in Doherty power amplifiers (DPA). Taking conduction angle and back-off (BO) level into account a global design chart is presented which can be utilized to properly dimension the aux amplifier. Based on the proposed method a class C power amplifier is designed and exploited in a DPA circuit at 28GHz which is evaluated using simulations based on 45nm CMOS technology. Simulations reveal 27dBm saturated output power, 60% maximum drain efficiency (DE), 45% DE at 6dB BO, and 2 times efficiency enhancement at 6dB BO which is a new record in this trend

Optimum number of transistors in stacked CMOS millimeter-wave power amplifiers

Abstract This paper proposes how to define the optimum number of stacked transistors in a multi-stacked CMOS power amplifier (PA) topology, based on several physical as well as circuit design aspects. Starting with a systematic concept, the analysis then goes through the relevance of transistor transconductance, aspect ratio, parasitics, operating frequency, and the number of transistor stages in a pentagonal trade-off concept. While this is done based on theoretical circuit analysis, the results, then, are evaluated using simulations based on 45nm CMOS technology