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Electrical Engineering in Japan 04/2007; 94(1):80 - 84. · 0.09 Impact Factor
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ABSTRACT: A simple analytical model is proposed and shown to be effective in predicting the nonlinear behavior of single-ended amplifiers, as well as Doherty amplifiers implemented with GaAs heterojunction bipolar transistors (HBTs) for handset applications. The analytical model is based on linear and nonlinear components extracted from a vertical bipolar inter-company model for Skyworks Solutions Inc.'s InGaP/GaAs HBT devices. Equations derived from the model provide insights into effects of individual components on the gain and phase of both the single-ended and Doherty amplifiers. The model indicates that tuning the phase delay inserted in front of the auxiliary power amplifier (PA) within the Doherty can improve linearity at a high input power. The efficacy of the model is demonstrated by experimental results in which, for a Doherty PA with a tuned phase delay at the auxiliary PA side, the measured gain and phase agree with the simulation results. Furthermore, the third-order intermodulation distortion performance is improved as much as 8 dB when compared with a Doherty PA without phase delay tuning
IEEE Transactions on Microwave Theory and Techniques 01/2007; · 1.85 Impact Factor
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K. W. Alt,
R. E. Yeats,
C. P. Hutchinson,
D. K. Kuhn,
T. S. Low, M. Iwamoto,
M. E. Adamski,
R. L. Shimon,
T. E. Shirley,
M. Bonse,
F. G. Kellert,
D. C. D'Avanzo
Microelectronics Reliability. 01/2007; 47:1175-1179.
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K.W. Alt,
R.E. Yeats,
C.P. Hutchinson,
D.K. Kuhn,
T.S. Low, M. Iwamoto,
M.E. Adamski,
R.L. Shimon,
T.E. Shirley,
M. Bonse,
F.G. Kellert,
D.C. D'Avanzo
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ABSTRACT: A novel circuit for measuring the infant mortality rate in InGaP/GaAs HBT technology is presented. The circuit allows reliability stressing to be performed on as many as 100,000 transistors per wafer and is necessary in order to predict the infant circuit failure rate in circuits with >500 transistors. This new circuit allows for the identification of failed transistors and subsequent failure analysis to allow for process improvements. Results show that substrate dislocations are the leading cause of infant mortality
ROCS Workshop, 2006. [Reliability of Compound Semiconductors]; 12/2006
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ABSTRACT: 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.
IEEE Transactions on Microwave Theory and Techniques 02/2005; · 1.85 Impact Factor
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ABSTRACT: This paper shows that current mode class-D (CMCD) amplifiers with integrated parallel LC resonator can achieve high efficiency at RF frequencies. In contrast to the conventional class-D amplifier, output shunt capacitance discharge loss is eliminated in a CMCD amplifier topology by satisfying the zero voltage switching (ZVS) condition. To reduce parasitic resistance, bondwires are utilized to implement a high Q inductor in the LC resonator. An experimental CMCD amplifier with collector efficiency of 78.5% at output power of 29.5dBm (0.89W) is demonstrated using GaAs HBTs at 700 MHz.
Microwave Symposium Digest, 2004 IEEE MTT-S International; 07/2004
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ABSTRACT: A power amplifier for CDMA applications which consists of a Doherty amplifier and a digital signal processing (DSP) controller is presented. DSP is used to dynamically adjust the gate bias of the auxiliary (peaking) amplifier at the rate of the signal envelope to obtain gain flatness (i.e. AM-AM distortion correction). Furthermore, DSP is used as a digital predistortor to improve the overall linearity by adjusting the phase at baseband (i.e. AM-PM distortion correction). The 840 MHz Doherty amplifier is realized with two commercially available MESFETs in a hybrid circuit, and the DSP is implemented externally with a board controlled by a personal computer. It is shown that by utilizing these DSP techniques, the overall linearity and efficiency characteristics of the Doherty amplifier can be significantly improved.
Microwave Symposium Digest, 2003 IEEE MTT-S International; 07/2003
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ABSTRACT: An analytical large-signal HBT model which accurately accounts for the intricate bias dependence of collector delay in devices fabricated in both GaAs and InP material systems is described. The strongly bias dependent collector delay function accounts for the variation of electron velocity with electric field of the collector, which has consequences for both the electron transit time and capacitance. It is shown that the new formulation significantly improves the prediction of the bias dependence of f<sub>t</sub>. As a result, simulations over a very wide range of operating conditions match measured data on a wide variety of devices. Distortion predictions are improved since the derivatives of the bias dependent delay are more accurately modeled. This new model is extracted on medium and high breakdown GaAs HBTs, and also on InP DHBTs. Simulation results are verified with comparisons to S-parameter and large-signal measurements.
Microwave Symposium Digest, 2003 IEEE MTT-S International; 07/2003
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ABSTRACT: High-frequency distortion in bipolar transistors is examined by using the charge-control approach of Poon and Narayanan (H.C. Poon, IEEE Trans. Electron Dev., vol. ED-19, pp. 719-731, 1972; S. Narayanan and H.C. Poon, IEEE Trans. Circuit Theory, vol. CT-20, pp. 341-351, 1973; H.C. Poon, IEEE Trans. Electron Dev., vol. ED-21, pp. 110-112, 1974) to connect the device's distortion behavior to its "loaded" unity-current-gain frequency (ωˆ<sub>T</sub>). The resulting expressions for the distortion reveal considerable information on its frequency and bias dependence. Points on the ωˆ<sub>T</sub> versus collector current curve yielding optimum distortion performance are identified and interpreted in terms of current cancellation. Both second- and third-order distortion are considered, and the results are validated by both simulation and experiment.
IEEE Transactions on Microwave Theory and Techniques 03/2003; · 1.85 Impact Factor
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ABSTRACT: A design strategy for a linear broad-band InGaP/GaAs heterojunction bipolar transistor (HBT) power amplifier is presented. This design is based on the bias dependence of the nonlinear base-collector charge, as expressed in the C<sub>BC</sub> versus V<sub>CE</sub> and τ<sub>C</sub> versus I<sub>C</sub> characteristics of the device. Using this technique, it is shown that the second- and third-order distortions have separate optimum bias conditions and, furthermore, there is an inherent tradeoff in optimizing the second- and third-order distortions. The strong bias dependence of the nonlinear base-collector charge and the tradeoff between the different orders of distortion are verified on two 24-dBm 0.5-11-GHz distributed power amplifiers optimized for second and third-order distortions, respectively. The experimental results show that the harmonic and intermodulation levels are sensitive to the different order derivatives of the f<sub>t</sub> versus I<sub>C</sub> curve. Specifically, second-order distortion is related to the slope of the f<sub>t</sub> versus I<sub>C</sub> curve and third-order distortion is related to both the slope and curvature of the f<sub>t</sub> versus I<sub>C</sub> curve. This design technique suggests the importance of HBT device design to minimize distortion in high-frequency broad-band amplifier designs. Furthermore, to minimize high-frequency distortion in HBT amplifiers across a wide range of bias, it is desirable to linearize the base-collector charge, where flat C<sub>BC</sub> versus V<sub>CE</sub> and f<sub>t</sub> versus I<sub>C</sub> characteristics are ideally desired.
IEEE Transactions on Microwave Theory and Techniques 01/2003; · 1.85 Impact Factor
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ABSTRACT: A design strategy for a linear broadband InGaP/GaAs HBT power amplifier is presented. This design takes advantage of the bias dependence of the nonlinear base-collector charge, expressed by the C <sub>BC</sub> vs V<sub>CE</sub> and τ<sub>c</sub> vs I<sub>c</sub> characteristics of the device. Using this technique, it is shown that the second and third order distortions have separate optimum bias conditions, and furthermore, there is an inherent tradeoff in optimizing the second and third order distortions. This strong bias dependence of the nonlinear base-collector charge and the tradeoff between the different orders of distortion are verified on a 24 dBm 0.5-11 GHz distributed power amplifier. To minimize high frequency distortion in HBT amplifiers across a wide range of bias, it is imperative to linearize the base-collector charge, where flat C<sub>BC</sub> vs V<sub>CE</sub> and f<sub>t</sub> vs I<sub>c</sub> characteristics are ideally desired
Microwave Symposium Digest, 2002 IEEE MTT-S International; 02/2002
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ABSTRACT: It is shown that a simple extension of the conventional behavioral
characterization of amplifier nonlinearity can be used to quantify power
amplifier performance including many memory effects. External variables
that influence the amplifier behavior (such as power supply voltage,
input bias or temperature) are identified. Measurements of gain and
phase (AM-AM and AM-PM conversion) are subsequently made over a range of
these external variables. The variation of the external variables is
explicitly taken into account with linear equivalent circuits at
baseband. The method is shown to be useful for the estimation of bias
circuit effects and self-heating effects
Microwave Symposium Digest, 2002 IEEE MTT-S International; 02/2002
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ABSTRACT: With RF pulsewidth modulation, microwave signals are encoded in a
binary signal having one pulse per period of the microwave signal, in
which the pulse timing varies with the phase of the RF signal, and the
pulse width varies in accordance with the signal amplitude. RF
pulsewidth modulated signals are advantageous for use with high
efficiency amplifiers (class D switching mode amplifiers or class C
amplifiers) for the quasi-linear amplification of signals with
time-varying envelope. This paper demonstrates a digital technique to
generate RF pulse modulated signals for narrowband microwave signals
such as those used in wireless communications. The technique makes use
of delta-sigma modulation of the phase and amplitude of the signal. The
generation of OQPSK signals is shown as an example. The approach is a
candidate for the design of single-chip, DSP-based transmitters
Microwave Symposium Digest, 2002 IEEE MTT-S International; 02/2002
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ABSTRACT: An extension of the Doherty amplifier, which maintains high
efficiency over a wide range of output power (>6 dB), is presented in
this paper. This extended Doherty amplifier is demonstrated
experimentally with InGaP/GaAs heterojunction bipolar transistors at 950
MHz. Power-added efficiency (PAE) of 46% is measured at P<sub>1dB</sub>
of 27.5 dBm and 45% is measured at 9 dB backed off from P<sub>1dB</sub>.
Additionally, PAE of at least 39% is maintained for over an output power
range of 12 dB backed off from P<sub>1dB</sub>. This is an improvement
over the classical Doherty amplifier, where high efficiency is typically
obtained up to 5-6 dB backed off from P<sub>1dB</sub>. Compared to a
single transistor class-B amplifier with similar gain and
P<sub>1dB</sub>, the extended Doherty amplifier has PAE 2.6 ×
higher at 10 dB back off and 3 × higher at 20 dB back off from P
<sub>1dB</sub>. Under different bias and output matching conditions, the
amplifier was also evaluated with CDMA signals. At the highest measured
power of 25 dBm, the extended Doherty amplifier achieves a PAE of 45%
with an adjacent channel power ratio of -42 dBc. Generalized design
equations are also derived and the consequences of finite device output
impedance on amplifier gain and linearity are explored
IEEE Transactions on Microwave Theory and Techniques 01/2002; · 1.85 Impact Factor
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ABSTRACT: The advance of CMOS-based digital circuits enables new strategies for optimisation of wireless transmitters. Co-design of DSP algorithms and power amplifier characteristics can lead to improved efficiency and linearity through a variety of strategies, including: a) DSP control over bias conditions, particularly the power supply voltage; b) predistortion, in simple amplifiers, and in compound architectures such as LINC and Doherty amplifiers; and c) DSP generation of digital input signals for switching amplifiers. We envision for the future a generation of "smart power amplifiers" in which DSP optimization of amplifier parameters is carried out for changing environments.
Microwave Conference, 2001. 31st European; 10/2001
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ABSTRACT: This paper demonstrates a high speed digital technique to produce
binary (digital) signals that encode representative RF signals (with
time varying envelope) as needed for wireless communications.
Specifically, it shows that IS-95 format CDMA signals can be generated
with a single bit digital data stream at 3.6 Gb/S. The technique uses
band-pass delta-sigma modulation so that the quantization noise is
shaped out of the frequency band of interest. This approach points the
way to single-chip, DSP-based transmitters, used in conjunction with
switching mode power amplifiers and simple analog filters, to implement
all the functions of a wireless transmitter
Microwave Symposium Digest, 2001 IEEE MTT-S International; 02/2001
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ABSTRACT: An extension of the Doherty amplifier architecture which maintains high efficiency over a wide range of output power (>6 dB) is presented. This extended Doherty amplifier is demonstrated experimentally with InGaP-GaAs HBTs at a frequency of 950 MHz. P<sub>1 dB</sub> is measured at 27.5 dBm with PAE of 46%. PAE of at least 39% is maintained for over an output power range of 12 dB backed-off from P<sub>1 dB</sub>. This is an improvement over the classical Doherty amplifier, where high efficiency is typically obtained up to 5-6 dB backed-off from P<sub>1 dB</sub>. Generalized design equations for the Doherty amplifier are derived to show a careful choice of the output matching circuit and device scaling parameters can improve efficiencies at lower output power
Microwave Symposium Digest, 2001 IEEE MTT-S International; 02/2001
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ABSTRACT: The linearity characteristics of GaAs heterojunction bipolar
transistors (HBTs) are studied through measurement and analysis.
Third-order intermodulation distortion behavior of HBTs is examined on
devices with various epilayer designs and at various bias points, loads,
and frequencies. Calculations from an analytical model reveal a strong
bias and load dependence of third-order intercept point (IP3) on the
nonlinearities from transconductance and the voltage dependence of
base-collector capacitance. However, a simple model is not able to
predict the fine details of IP3 with bias. A large-signal HBT model with
an accurate description of the base-collector charge is shown to account
for the measured trends. The base-collector charge function accounts for
the modulation of base-collector capacitance with current, electron
velocity modulation, and the Kirk effect (base pushout) for GaAs-based
HBTs. A detailed study of the influence of collector design on linearity
is also presented
IEEE Transactions on Microwave Theory and Techniques 01/2001; · 1.85 Impact Factor
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ABSTRACT: A class-S amplifier with a bandpass delta-sigma modulated input is
demonstrated using CMOS devices at 10 MHz. With a two-tone modulated
input, third-order intermodulation products below -40 dBc were measured,
with an output power of 26 dBm and a drain efficiency of 33%. This new
amplifier topology demonstrates promising performance for simultaneously
achieving high linearity and efficiency
Electronics Letters 07/2000; · 0.96 Impact Factor
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ABSTRACT: Linearity characteristics of InGaP/GaAs heterojunction bipolar
transistors with various collector profiles are examined. Output
third-order intercept point is measured as a function of bias current
and voltage at 5 GHz. The results from this study indicate that IP3
varies with current in a complex manner and is significantly dependent
on the collector design. A dynamic trend in IP3 is observed where a peak
occurs at a current just below Kirk effect and a trough occurs at the
onset of Kirk effect. Although the Gummel-Poon model is not able to
predict this behavior, a large signal HBT model, which accounts for
collector space-charge effects such as electron velocity modulation and
Kirk effect, can properly represent the measured data. For accurate
linearity predictions, these effects should be included in a large
signal HBT model
Microwave Symposium Digest. 2000 IEEE MTT-S International; 02/2000
