N.B. de Carvalho

Large- and small-signal IMD behavior of microwave power amplifiers

In this paper, large-signal intermodulation distortion (IMD) sweet spots in microwave power amplifiers are studied and predicted using a new mathematical basis. The variations in the IMD versus drive pattern with active bias point and the terminating matching networks are investigated. This nonlinear distortion model enabled the design of power amplifiers specially tailored to present a desired IMD versus drive-level pattern. For practical validation purposes, a MESFET case study and an illustrative application example are presented.

Prediction of IMD in LDMOS transistor amplifiers using a new large-signal model

In this paper, the intermodulation distortion (IMD) behavior of LDMOS transistors is treated. First, an analysis is performed to explain measured IMD characteristics in different classes of operation. It is shown that the turn-on region plays an important role in explaining measured IMD behavior, which may also give a clue to the excellent linearity of LDMOS transistors. Thereafter, with this knowledge, a new empirical large-signal model with improved capability of predicting IMD in LDMOS amplifiers is presented. The model is verified against various measurements at low as well as high frequency in a class-AB power amplifier circuit.

A comprehensive analysis of IMD behavior in RF CMOS power amplifiers

This paper presents a comprehensive analysis of nonlinear intermodulation distortion (IMD) behavior in RF CMOS power amplifiers (PAs). Separate analyses are presented for small- and large-signal operation regimes. Especially, a new, simple, large-signal behavioral IMD analysis method is presented that allows the mechanisms dominant for IMD generation to be identified and their individual contributions to be studied. By combining these analyses, typical IMD versus input power characteristics of MOSFET PAs can be predicted and understood for different classes of operation. Various measurements made on a 950-MHz RF CMOS PA are used to demonstrate typical behavior and validate the proposed theory. Prediction of IMD using a standard CMOS transistor model is also evaluated and is shown to give good agreement with the measurements.

Multitone frequency-domain simulation of nonlinear circuits in large- and small-signal regimes

Computer simulation of general microwave nonlinear circuits excited by a large number of input tones is addressed, The algorithm, based on the spectral-balance method, uses novel index-vector and convolution-matrix generation techniques. That, in conjunction with a new nonlinear-device modeling approach (which directly takes into account the higher order derivatives of the I/V and Q/V characteristics), allowed the prediction of such complex behavior as spectral regrowth and noise-power ratio (NPR) tests of a class-B power amplifier or multitone intermodulation phenomena in a saturated multioctave amplifier.

Characterizing the gate-to-source nonlinear capacitor role on GaAs FET IMD performance

This paper discusses the gate to source nonlinear capacitor contribution on small signal intermodulation distortion (IMD) performance of FET devices. The second and third order coefficients for the Cgs(Vgs) Taylor-series expansion, experimentally extracted with a simplified one-sided version of our previously proposed test set-up, are shown to be responsible for some detected differences on IMD behaviour at high frequencies.

Resistive FET mixer conversion loss and IMD optimization by selective drain bias

This paper describes a dedicated nonlinear MESFET model extraction technique, which was used to accurately characterize the devices channel resistance nonlinearity. Plotting Ids(Vgs,Vds) Taylor series expansion coefficients across V/sub GS/ and V/sub DS/ revealed not only the presence of important minimum conversion loss bias, but also of in-band IMD sweet spots that were then used to optimize a FET resistive mixer performance.

Intermodulation distortion behavior in LDMOS transistor amplifiers

An analysis of the intermodulation distortion (IMD) behavior of LDMOS transistor amplifiers is presented. It is shown that the turn-on region abruptness compared to most other devices is important for explaining the measured IMD behavior such as sweet-spots. The analysis is validated using two-tone measurements at low frequency for different classes of operation. A 1.9 GHz LDMOS power amplifier is designed and characterized to investigate the IMD behavior also at higher frequency.

Characterizing nonlinear RF circuits for their in-band signal distortion

This work presents a theoretical discussion on the ability of traditional noise power ratio (NPR) setups to characterize the in-band signal distortion of general RF circuits. It is shown that NPR tests are optimistic in estimating co-channel distortion, as they are blind for the signal-correlated components. Therefore, an alternative standard for co-channel distortion specification and the associated measurement setups are theoretically proposed and experimentally validated.

Large signal IMD sweet spots in microwave power amplifiers

In this paper, large signal IMD sweet spots in microwave power amplifiers are investigated and predicted using a new mathematical basis. This type of nonlinear model enabled the design of power amplifiers specially tailored to present a desired IMD versus drive level pattern. Finally, illustrative application examples are presented.

Noise and distortion figure - an extension of noise figure definition for nonlinear devices

Deals in the integration of additive and nonlinear distortion noise contributions into a single new figure of merit: Noise and Distortion Figure, NDF. In the same way as traditional noise figure, NF, was conceived to be a measure of SNR degradation, NDF is now proposed as its extension to nonlinear systems, as a measure of SINAD degradation. NDF definition is discussed and its application to SINAD evaluations in systems of practical interest to the wireless community is exemplified.