Olav Andersen

Nonlinear Characterization of Multiple Carrier Power Amplifiers

In this paper the input signal dependence on the nonlinear transfer function of power amplifiers is discussed. It is shown by measurements that the nonlinear behavior of the amplifier does indeed depend on the input signal. This is seen to be true both for AM/AM and AM/PM distortion. The implication is that a traditionally VNA swept CW cannot be used to obtain the AM/AM and AM/PM distortion that will actually take place in the amplifier during real life conditions, and that test signals which closely resembles the signals that will actually be used are necessary. The focus is to present a new possible measurement methodology necessary to target the demands of accurate characterization raised by multiple carrier power amplifiers MCPA:s. We briefly discuss the mechanisms that lies behind this behavior. The test signal selection and creation is discussed, as well as a method of producing highly linear ¿80 dBc WCDMA signals for ACP testing. Finally we present practical measurement results on AM/AM and AM/PM distortion obtained with swept, pulsed and multi-tone input signals to prove the input signal dependence. Practical results is given for high power narrowband Class AB LDMOS amplifiers intended for the 2.11-2.17GHz WCDMA band and for medium power Class A GaAs FET amplifiers.

A test-bed designed to utilize Zhu's general sampling theorem to characterize power amplifiers

Characterizing power amplifiers require test set-ups with performance superior to the power amplifiers. A commonly used method is to use an IQ-demodulator. However, problem arises due to imperfections in the demodulator such as IQ-imbalance; an alternative method is to use a direct down converter to intermediate frequency. The drawback then is the limited bandwidth. However, the required bandwidth of the ADC does not need to be exceptional. According to Zhus general sampling theorem is it enough to sample the output signal at the Nyquist rate of the input. However, even though the required sampling rate is reduced the demands on the analog bandwidth remains. Unfortunately, commercially available instruments such as vector signal analyzers can not be used for this purpose since their analog bandwidth is too small. In this paper a test-bed is designed to utilize the Zhus general sampling theorem. The RF front-end has frequency range of 500 MHz - 2.7 GHz and a bandwidth of 1 GHz. All performance data are verified with measurements.

Wideband characterization of power amplifiers using undersampling

In this paper a radio frequency power amplifier is measured and characterized by the use of undersampling based on the generalized Zhu-Frank sampling theorem. A test system has been designed allowing the bandwidth of the stimuli signal to be 100 MHz in the characterization process. That would not be possible with any vector signal analyzer on the market. One of the more challenging problem within the proposed concept is the model validation process. Here, two different techniques for model validation are proposed, the multitone and the spectrum scan validation methods.

Measurement of ACLR with high dynamic range

In this paper a method to overcome the insufficient dynamic range of RF measurement instruments, i.e. signal generators and spectrum analyzers, for distortion measurements on feedforward and other highly linear amplifiers, is discussed. A circuit board is designed, built and verified. Its performance is found to be superior to traditional methods using filters, both from a technical performance and flexibility standpoint as well as from an economic view. ACLR measurements for WCDMA signals can be done well below −70 dBc using the produced circuit board.

Automated multidimensional characterization of power amplifier for design and production

Designing, optimizing and producing modern power amplifiers (PA) requires new and fast RF (radio frequency) measurement techniques capable of characterizing its real behavior. PAs are a truly multidimensional device where many desired performance parameters are contradictory to each other. This is especially true for the generation of modern communication PAs that require high efficiency, high linearity as well as high bandwidth. This paper presents a software-defined measurement setup for fast and cost efficient multidimensional measurements based on highly accurate standard instruments and a PC. The test bed as well as the graphical user interface is presented along with a demonstration of its functionality. During tuning of tank networks, drain quiescent current, and bias conditions, 3-dimensional graphs can be selected for the most appropriate axes of trade-off parameters to display a true behavior of the PA under test subjected to real-world or close to real-world signals. The measurement system offers the possibility to monitor envelope-tracking dynamic power consumption up to 100 MHz plus the possibility to use high crest factors.

Nonlinear network analysis for modern communication devices and systems

This paper presents a novel test setup, based on a vector signal generator (VSG) and a vector signal analyzer (VSA), capable of nonlinear characterization of communications devices such as RF power amplifiers. Envelope time-domain waveform extraction and correction is applied to the DUT reference plane, preserving vector correction even in modulated environments where ingoing and outgoing signals from the ports of the DUT can be distinguished. This tool is valuable in the analysis of nonlinear devices, the generation of behavioral models and the study of memory effects..

An envelope domain measurement test setup to acquire linear scattering parameters

In this paper, the functionality of a vector network analyzer VNA is implemented using the concept of software defined measurements (SDM) [1], called SDM-VNA. A general measurement set-up based on a vector signal generator (VSG) and a vector signal analyzer (VSA) is used. The set-up allows complete linear characterization using only one receiver. A calibration procedure to remove the systematic errors is applied to the results and compared with a modern VNA, showing good agreement.

Extending the Bandwidth and Dynamic Range of Old RF Instruments to Meet State-of-the-Art Performance, Using a Synthetic Instrument Approach

A decrease in life cycle cost is a key issue for testing mobile communication systems. The rapid development and edge technology requires high-performance instruments and state-of-the-art measurement technology. New investments are expensive, but even older generation instruments are capable of extending their bandwidth and dynamic range to meet even the latest third-generation partnership project (3GPP) cellular measurement requirements by the addition of external hardware using a synthetic instrument approach. The novelty of this paper is the high performance on the most crucial parameters, i.e., the dynamic range and bandwidth achieved by only replacing some parts of the legacy instrument. Moreover, the demonstrated direct IF synthesis has a high degree of novelty at wide modulation bandwidths. It is desired to use virtual/synthetic instruments and make the signal processing in the software independent of the hardware, i.e., software-defined measurements (SDMs). In this paper, a state-of-the-art experimental setup for signal generation and signal analysis is demonstrated. A direct IF synthesis is used to generate a wideband code-division multiple-access (WCDMA) carrier with more than 72-dB adjacent carrier leakage ratio (ACLR) up to 12 parallel carriers with more than 68-dBc ACLR over a total bandwidth of 100 MHz. The signal analysis capabilities (e.g., ACLR performance) for a WCDMA carrier is better than -70 dBc and for a continuous wave better than -85 dBc over a bandwidth of 42.5 MHz. The critical RF downconverter in the setup is carefully designed not to degrade the dynamic range performance.