Peter J. Zampardi

Design of high-efficiency current-mode class-D amplifiers for wireless handsets

Design considerations are discussed for current-mode class-D (CMCD) microwave power amplifiers. Factors affecting amplifier efficiency are described analytically and via simulation. Amplifiers are reported that incorporate parallel LC resonators alongside the switching transistors. To reduce parasitic resistance, bond-wires were utilized to implement a high Q inductor in the LC resonator. An experimental CMCD amplifier based on GaAs HBTs is reported, with collector efficiency of 78.5% at an output power of 29.5 dBm (0.89 W) at 700 MHz.

A comparison of the effects of gamma irradiation on SiGe HBT and GaAs HBT technologies

A comparison of the effects of gamma irradiation on silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) and gallium-arsenide (GaAs) HBT technologies is reported, DC and radiofrequency (RF) performance as well as the low frequency noise are investigated for gamma doses up to 1 Mrad(Si). The results indicate that both SiGe and GaAs HBT technologies are tolerant to gamma irradiation.

Experimental procedure to optimize out-of-band terminations for highly linear and power efficient bipolar class-AB RF amplifiers

An optimization procedure based on load-pull measurements to obtain both highly-linear and highly-efficient class-AB operation is presented. This procedure can be applied without any foregoing device characterization; therefore it is an excellent method to compare the linearity performance of different bipolar technologies. The presented approach provides the optimum out-of-band terminations and quiescent current yielding IM3 improvement of more than 15 dBc at 3 dB back-off compared to traditional design techniques. Optimum power-added efficiency is achieved at the same time.

A GaAs Junction Varactor With a Continuously Tunable Range of 9 : 1 and an

In this letter, a junction varactor is presented with a large capacitance tuning range, while providing very high linearity. Such varactors are extremely useful in adaptive RF applications, which directly benefit from passive components with high tuning range and high linearity. Using a preproduction GaAs process technology and third-order intermodulation (IM 3) cancellation techniques, a very linear device is created with a capacitance tuning range as large as 9 : 1 over a control voltage range from 0 to 15 V. Its third-order output intercept point is 57 dBm; the average quality factor is ~ 50, and the breakdown voltage is 28 V. These measured results represent the current state-of-the-art in tuning range, linearity, and quality factor among all existing continuously tunable elements.

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In this paper, we present a discussion and comparison of CMOS and GaAs HBT technologies for handset power amplifiers. Our perspective is unique to other comparisons in that we actually have products in both technologies. To understand the application space where each of these technologies makes sense, we discuss current and near-term PA requirements as well as technology and technology support issues. Finally, we aim to dispel some the common misperceptions surrounding these technologies.

of 57 dBm

Adaptive Digital Predistortion (DPD) is applied to a spec-compliant class-AB GaAs HBT PA module for WCDMA handsets. It is shown that, by using a re-optimized load line, the efficiency can be increased from 37.5% to 47% at nominal 28.5 dBm output power, while maintaining the same excellent linearity of the original PA. The quiescent current consumption is also reduced down to 40 mA at all power levels, enabling up to 49% average dc power savings without dynamic biasing. Under 2∶1 VSWR, 7% to 11% higher PAE is demonstrated at 28 dBm, achieving significant ACPR reduction as well. The methodology to tradeoff the linearization capability of DPD to optimize efficiency at a specified power and linearity is discussed in detail.

Will CMOS amplifiers ever Kick-GaAs?

A novel method for determining the junction capacitances versus voltage in heterojunction bipolar transistors (HBTs) using s-parameters at microwave frequencies is presented. This new technique has several advantages over traditional approaches, which include: (1) it profiles capacitance at greater forward bias; (2) it enables the direct measurement of minimum geometry transistors; (3) it allows for the accurate extraction of scaled HBT model parameters with emitter length; and (4) it results in improved pad parasitic deembedding for accurate modeling. Both the capacitance-voltage and large-signal HBT model results are shown.

Efficiency improvement of a handset WCDMA PA module using Adaptive Digital Predistortion

In this letter, the influence of the RF voltage swing on the effective capacitance of continuously tunable capacitive devices, e.g., varactors, is investigated. Using Volterra series, equations are derived that describe the change in effective capacitance versus RF voltage, which are in agreement with simulations and have been verified by measurements. Comparing conventional and IM3 compensated varactor configurations, significant differences are found for their capacitance variation versus power. It is found that an anti-series configuration of two varactors with exponential C(VR) behavior and proper center-tap termination outperforms all other known varactor configurations and shows a maximum capacitance variation below 0.1% compared to 10% for conventional varactor elements using identical excitation.

Direct measurement of C/sub be/ and C/sub bc/ versus voltage for small HBT's with microwave s-parameters for scaled Gummel-Poon BJT models

For the implementation of RF tunable components, semiconductor based varactors provide advantages in terms of low control voltage, high capacitance density, low packaging costs, high reliability and technology compatibility. In this paper, an overview is given of the linearization approaches for semiconductor based ultra-linear varactors. Implementation issues regarding the optimum doping profiles are discussed. Design considerations for dedicated bias networks that provide optimum third-order intermodulation cancellation for the various varactor configurations are presented. To give an indication of the system-level responses for linear varactors, a varactor-based “true” time delay phase shifter is designed and the system-level linearity parameters, like adjacent channel power ratio (ACPR) and error vector magnitude (EVM), are evaluated for various application conditions.

RF Power Insensitive Varactors

Three layout-based techniques designed to equalize the temperature distribution in GaAs HBT output arrays of Power Amplifiers (PAs) are evaluated. Electrothermal simulation results show that a reduction in the range of 4–5% of the peak of the junction temperature rise over ambient can be achieved with a negligible increase in design complexity and area, and that up to 7% can be obtained by further optimizing the distribution of base ballast resistors. This is a positive outcome in regards to long-term device reliability since the probability of a failure is reduced when the highest junction temperature in the array is decreased. However, and extensive experimental characterization of PAs incorporating the array variants reveals that the temperature reductions are too low to yield quantifiable improvements in RF performance and ruggedness.