Large Signal Network Analyzer Research Articles

1/f Additive Phase Noise Analysis for One-Port Injection-Locked Oscillators

The 1/f additive phase noise of one-port injection-locked oscillators is experimentally characterized and analyzed using a simple analytic model based on the generalized 1/f Kurokawa theory. To experimentally verify the prediction of the simple analytic model proposed, two negative-conductance transmission line pHEMT oscillators operating at 2.4828 GHz and 2.485 GHz were designed and fabricated. A new configuration for integrating an additive phase noise measurement system with a large signal network analyzer (LSNA) is introduced to jointly acquire both the noise and RF waveforms of the one-port injection-locked oscillator. The Kurokawa derivatives needed for the analytic expression were experimentally obtained using the LSNA measurements and optimized to accurately model the corner frequency. A good agreement between the predicted and experimental results was obtained for both the injection-locked and free-running oscillators. In contrast to phase noise measurements of the free-running oscillator, which can only characterize the oscillator-upconverted 1/f3 noise, the additive phase noise characterization of the injection-locked oscillator is shown to provide the means to directly observe and characterize the input-referred intrinsic 1/f noise source of the oscillator negative resistance.

A streamlined drain-lag model for GaN HEMTs based on pulsed S-parameter measurements

AbstractAccurately and efficiently modeling the drain-lag effects is crucial in nonlinear large-signal modeling for Gallium Nitride high electron mobility transistors. In this paper, a simplified yet accurate drain-lag model based on an industry standard large-signal model, i.e., the Chalmers (Angelov) model, extracted by means of pulsed S-parameter measurements, is presented. Instead of a complex nonlinear drain-lag description, only four constant parameters of the proposed drain-lag model need to be determined to accurately describe the large impacts of the drain-lag effects, e.g., drain-source current slump, typical kink observed in pulsed IV curves, and degradation of the output power. The extraction procedure of the parameters is based on pulsed S-parameter measurements, which allow to freeze traps and isolate the trapping effects from self-heating. It is also shown that the model can very accurately predict the load pull performance over a wide range of drain bias voltages. Finally, the large-signal network analyzer measurements at low frequency are used to further verify the proposed drain-lag model in the prediction of the output current in time domain under large-signal condition.

A procedure for the extraction of a nonlinear microwave GaN FET model

SummaryIn this paper, we describe an extraction procedure of nonlinear models for microwave field‐effect transistor (FET). We use a nonlinear model available in commercial CAD tools, and we extract the parameters by combining direct extraction and numerical optimization. We determine a first estimate of the model parameters by few DC and S‐parameter measurements. Next, we refine the parameters by optimization against low‐frequency and high‐frequency vector‐calibrated large‐signal measurements gathered with a Large‐Signal‐Network Analyzer (LSNA). As case study we consider a 0.25 × 200 µm2 GaN FET on SiC for power amplifier applications. Ultimately, we want to show that a good accuracy level can be achieved while minimizing the extraction effort and that an accurate model can be built and suitably tailored depending on the final application. Copyright © 2016 John Wiley & Sons, Ltd.

Comparing LSNA Calibrations: Large-Signal Network Analyzer Round Robin

Comparing LSNA Calibrations: Large-Signal Network Analyzer Round Robin

A Three-Port Nonlinear Dynamic Behavioral Model for Supply-Modulated RF PAs

We propose a three-port nonlinear dynamic behavioral model for supply-modulated power amplifiers (PAs). The proposed model not only accounts for the radio frequency (RF) input-output relationship, but also for the interaction between a modulated voltage supply, the RF output power and the supply current. The model is based on a modified Volterra formulation which accounts for the dynamic deviations with respect to a quasi-static model. The frequency-domain kernels of the proposed model are directly extracted from measurements performed with a low-frequency-extended large-signal network analyzer on an RF hand-set PA. The model is validated under random multitone modulated RF input and supply. The presented technique allows for the independent control of the RF and the supply ports. As such, it allows a separate description of both the dynamic contribution of the RF modulated input and of the dynamic supply voltage. The proposed model shows an improvement with respect to a quasi-static approach in predicting the RF output, the supply current, as well as the power-added efficiency.

Design of injection‐locked oscillator circuits using an HBT X‐parameters™‐based model

A load independent X-parameters-based heterojunction bipolar transistor (HBT) model has been used for the first time in the design and behaviour prediction of injection-locked oscillator circuits. This model has been extracted from load-pull measurements with a large-signal network analyser and, in order to obtain a high oscillator RF power, targeting a load impedance close to the optimum one for HBT maximum output power. A methodology is given to obtain robust injection-locked oscillator circuits with a high-synchronisation bandwidth. Several injection-locked oscillator prototypes have been designed and fabricated, and their measurements compared with the simulations obtained using the X-parameters model. Satisfactory results were obtained when the prototypes were operated as free-running and synchronised oscillators.

A New NVNA Phase Reference for Polyharmonic Intermodulation Measurements

The step-recovery-diode-based impulse generator is a classical picosecond-level impulse-formation technique, whose strong harmonic nonlinearity under sinusoidal stimulus is widely utilized as the phase reference of the nonlinear vector network analyzer (VNA) (NVNA) and large-signal network analyzer for wideband measurements. This paper further exploits its intermodulation nonlinearity under multitone stimulus and proposes a new approach, rather than the traditional “harmonic” way, of the NVNA phase reference for future polyharmonic intermodulation measurements. Experimental results show that this method can provide plentiful intermodulation components around each harmonic available and is stable for NVNA use, with the advantages of flexible local frequency-resolution setup from tens of megahertz to less than hundreds of hertz.

Diode power detector X‐parameters™ model extraction using LSNA‐based measurement system

A study is presented on the problems that may arise when characterising low frequency device behaviour with a large signal network analyser (LSNA)-based measurement system. A diode power detector has been measured and, for the first time, an X-parameters based detector model was extracted from measurements. Difficulties measuring the detector output voltage dependence with baseband impedances, especially when those impedances showed resonant effects, were observed and a method to overcome the problems encountered is presented. The measurement-based detector X-parameters model demonstrated its usefulness to predict power detector behaviour under two-tone excitations and complex loads.

Two-Stage GaN HEMT Amplifier With Gate–Source Voltage Shaping for Efficiency Versus Bandwidth Enhancements

In this paper a two-stage 2-GHz GaN HEMT amplifier with 15-W output power, 28-dB power gain, and 70% power-added efficiency (PAE) is presented. The power stage is designed to operate under class F conditions. The driver stage operates under class F-1 conditions and feeds the power stage with both fundamental and second harmonic components. The inter stage matching is designed to target a quasi-half sine voltage shape at the intrinsic gate port of the power stage. The goal is to reduce aperture angle of the power stage and get PAE improvements over a wide frequency bandwidth. In addition to the amplifier design description, this paper reports original time-domain waveform measurements at internal nodes of the designed two-stage power amplifier using calibrated high-impedance probes and large signal network analyzer. Furthermore, waveform measurements recorded at different frequencies show that aperture angle remains reduced over large frequency bandwidth. In this study, a PAE greater than 60% is reached over 20% frequency bandwidth.

Power Handling Analysis of High-Power $W$-Band All-Silicon MEMS Phase Shifters

This paper analyzes the power handling capability and the thermal characteristics of an all-silicon dielectric-block microelectromechanical-system (MEMS) phase-shifter concept, which is the first MEMS phase-shifter type whose power handling is not limited by the MEMS structures but only by the transmission line itself and by the heat-sink capabilities of the substrate, which enables MEMS phase-shifter technology for future high-power high-reliability applications. The power handling measurements of this concept are performed up to 43 dBm (20 W) at 3 GHz with an automatic gain-controlled setup, assisted by a large-signal network analyzer, and the temperature rises of the devices were measured with an infrared microscope camera. The measurement results are extended to 40 dBm at 75 GHz by calibrating electrothermal simulations with the measurements. A comparative study to conventional state-of-the-art MEMS phase-shifter concepts based on thin metallic bridges is carried out. The simulated results show that the all-silicon phase-shifter designs have the maximum temperature rise of only 30°C for 40 dBm at 75 GHz, which is 10-20 times less than conventional MEMS phase shifters of the comparable RF performance.

Harmonic Sampling and Reconstruction of Wideband Undersampled Waveforms: Breaking the Code

In this paper, a method for measuring wideband waveforms correctly when undersampling is used as a digitizing technique is presented. Two major challenges arise when undersampling wideband waveforms: overlapping of aliased spectral bins of the digitized waveform and ambiguity in spectral bins standing on multiples of the Nyquist frequency. Those challenges are more pronounced when using wideband modulated signals to excite nonlinear devices. The theory behind a correct undersampled measurement is based on the use of an irrational relation between the undersampling frequency and the spectral resolution of the waveform to measure. This is the key to a successful harmonic sampling used today in large-signal network analyzers when wideband modulated waveforms are to be measured. Inverting the problem, such theory is also the solution for reconstructing wideband undersampled waveforms based on a single measurement and with a relatively short record of measured data. It is a solution for RF sampling and cognative radios where the digital processing is moving toward the antenna of the receiver.

Pulsed-IV Pulsed-RF Cold-FET Parasitic Extraction of Biased AlGaN/GaN HEMTs Using Large Signal Network Analyzer

A new pulsed-IV pulsed-RF cold field-effect transistor (cold-FET) technique is presented to extract the parasitics of AlGaN/GaN HEMTs under various quiescent dc-biasing points. The measurement system implemented with a large signal network analyzer applies the technique of multiple recording to acquire pulsed-RF small-signal S-parameters with no loss of dynamic range as the pulse duty cycle decreases. These cold-FET measurements are performed on unpassivated and silicon nitride (SiN) passivated devices by turning the device off for 1 ?s with a 1% duty cycle to analyze the impact of slow thermal and trapping effects on the device parasitics. The parasitic fringe capacitances extracted are found to be bias independent, except for the gate to drain capacitance in devices without SiN passivation. In unpassivated devices, the drain parasitic resistance is found to rapidly increase with increasing drain bias at negative gate to source voltages. On the contrary, in devices with SiN passivation, the dependence of the resistance with the drain bias voltage is much less significant. A simple physical model is used to fit the functional dependence of the 2-D electron gas (2DEG) concentration upon the gate-to-source and gate-to-drain voltages, which is then proposed for fitting the measured data. The analysis indicates that the variation of the resistance with bias voltage in the device studied with SiN passivation and also for the unpassivated device at V GS=0 V is well accounted for by the reduction of the mobility with increased temperature due to self-heating, whereas for the device studied without SiN passivation, the increase of the drain resistance with drain voltages at negative gate bias principally arises from the decrease of the 2DEG population in a narrow region near the gate contact. An equivalent circuit is also introduced to explain the decrease of the source and drain parasitic inductances with increasing drain voltages at large negative gate bias, which is observed in unpassivated devices.

Time domain model validation of a nonlinear block-oriented structure

A crystal detector is studied as a valid candidate reference element for the phase calibration of the large-signal network analyzer (LSNA) for modulated excitations. However, one cannot use a crystal detector straightforwardly as a phase reference element, since a crystal detector inherently introduces phase distortions. Hence, the identification and validation of a parametric black-box model of the detector is needed. In this work, a nonlinear feedback model for a crystal detector is constructed: the model contains a low-pass filter in the feedforward path and a Wiener system in the feedback loop. The model is estimated from baseband data and needs to be validated for use with high-frequency signals: the model needs to be extrapolated to RF frequencies, which is quite an arduous task. The validation of the extrapolated model is performed using two approaches: (i) the RF narrow band modulated signal is applied to the extrapolated model structure and the output signal is computed; (ii) the physical representation of the model structure is translated into its differential equation and by means of this equation, the low-frequency output envelope is computed for RF input signals. The second approach requires a slight modification of the extracted model compared to the model used in the first approach, with respect to the function describing the static nonlinear behavior. The deviation between the modeled output envelope and the measured output envelope is evaluated for both approaches. The method (ii) that computes the output of the detector in the time domain by means of solving a differential equation that characterizes the identified nonlinear feedback model gives the overall best results for predicting the magnitude and the phase of the detector output spectrum and the amplitude behavior of the time domain output waveform. The mean deviation in magnitude between the modeled and measured envelope equals 2.6 dB. This approach significantly outperforms the first method (i) as the mean deviation between the phase of the modeled and measured envelope equals 8.2°.

Pulsed Active Load–Pull Measurements for the Design of High-Efficiency Class-B RF Power Amplifiers With GaN HEMTs

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A novel pulsed class-B load–pull measurement system is developed to characterize GaN HEMTs targeting the design of high-efficiency class-B or class-C power amplifiers operating under a pulsed-bias and pulsed-RF (pulsed-<emphasis emphasistype="boldital">IV</emphasis>/RF) condition. Based on a large-signal network analyzer, the test system uses an active load–pull method to provide stable open-loop pulsed-RF loads into the drain at <formula formulatype="inline"> <tex Notation="TeX">$\omega_0$</tex></formula> and <formula formulatype="inline"> <tex Notation="TeX">$2\omega_0$</tex></formula> while bypassing slow-memory effects. The load–pull measurement data obtained from AlGaN/GaN HEMTs under the class-B operation reveal that there exist optimal loads for pulsed-<emphasis emphasistype="boldital">IV</emphasis>/RF condition, which differ from the ones found for a dc–<emphasis emphasistype="boldital">IV</emphasis> and continuous wave condition. This is due to the avoidance of slow-memory effects in the pulsed-<emphasis emphasistype="boldital">IV</emphasis>/RF load–pull measurements, which are known to degrade the device RF performance: a 2-dB increase in output power is obtained for a GaN HEMT on sapphire. The optimized pulsed-RF active load for a GaN HEMT on SiC demonstrates a power-added efficiency of 82% with 17.8-dBm output power under quasi class-B pulsed operation at 2 GHz. </para>

An Improved Broadband Conversion Scheme for the Large-Signal Network Analyzer

The key component of a large-signal network analyzer (LSNA) is the downconvertor, which allows the transformation of the measured RF spectrum into an IF spectrum by using the harmonic sampling principle. However, a drawback of the harmonic sampling principle is that, for broadband signals, a ldquodescramblingrdquo of the measured IF spectral components is necessary after downconversion. In this paper, the classical two-port LSNA is adapted to allow direct conversion of broadband signals. The necessary hardware adaptations are explained, and the improved broadband conversion is shown on some significant measurement examples.

Design and characterization of an RF pulse train generator for large-signal analysis

In this paper an RF pulse train signal is introduced that can serve as a reference signal for the phase calibration of the large-signal network analyser (LSNA) under modulated excitations. Hence, the pulse train generator is specifically designed to fulfil the requirements of such a calibration signal. The design and characterization of the RF signal generator are discussed in this work.

High-Power EMI on RF Amplifier and Digital Modulation Schemes

We present the performance of an RF amplifier and digital modulation techniques in the presence of high-power electromagnetic interference (EMI) to provide existing and next generation communication systems with critical information. An advanced measurement setup comprised of a large-signal network analyzer is used to characterize the adverse effects of EMI on the device characteristics of an RF power amplifier and the performance of digital modulation schemes. Furthermore, our analysis incorporated hybrid numerical tools, such as the hybrid S-parameter method to carry out an extensive EMI analysis of digital modulation schemes in the presence of complex structures, such as cylindrical cavities. Our studies yield critical information for the communication systems. For instance, our analysis suggests that digital modulation schemes are more susceptible to EMI than the RF power amplifier that processes the modulated signals. Power levels of the order of megawatts are required to have a notable impact on the device characteristics of an RF amplifier in the presence of a missile-like body, whereas, much lower power levels are sufficient to degrade the performance of a digital modulation scheme as long as it is within the bandwidth of the modulated signal. Our analysis further indicates that nonconstant envelope digital modulation schemes are more susceptible to EMI.

Measuring the response of a voltage-controlled oscillator using the large-signal network analyser

In this paper, a method is proposed for the direct measurement of the dynamic voltage-to-frequency transfer characteristic and the actual waveform of a voltage-controlled oscillator (VCO). Real-world measurements on a 1650 MHz unit over a 2 MHz frequency sweep show the applicability of the proposed technique.

On the use of a crystal detector for a phase calibration of the large signal network analyzer

This paper introduces a crystal detector as a new calibration standard for large signal analysis [1–4]. By means of the detector as a reference element one can calibrate the phase distortion of the large signal network analyser (LSNA) on a dense frequency grid. In this paper we estimate and validate a parametric black-box model for a crystal detector.

Nonlinear Characterization and Modeling of Carbon Nanotube Field-Effect Transistors

We report for the first time to our knowledge large-signal measurements performed at 600 MHz and in time domain on carbon nanotube field-effect transistors (CNFETs) using a large-signal network analyzer. To overcome the very high mismatch between the high CNFET impedance and the basic 50-Omega configuration of the setup, the output impedance was matched with the help of an experimental active load-pull configuration. Hence, we were able to observe under large-signal conditions the nonlinear behavior of CNFETs. Static measurements and continuous-wave <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ij</sub> -parameter measurements were made for many different biases. They were used in order to determine a nonlinear electrical model that has been validated thanks to the nonlinear measurements. The developed model opens the way for electrical CNFET circuit simulation and nonlinear applications of these devices.