196,208 research outputs found
Traditional molecular markers and response to adjuvant endocrine or trastuzumab-based therapies
No full textPurpose of review: The accurate assessment of traditional molecular markers is essential to inform the choice of the adjuvant systemic treatments for patients with breast cancer. Extensive research efforts have been made to explore whether it is also possible to predict the actual response to the different therapeutic options based on the expression of these markers. Recent findings: Endocrine responsiveness of breast cancer has been eventually defined according to the expression of estrogen receptors in at least 1% of invasive tumor cells. The quantitative evaluation of estrogen receptors, progesterone receptors (PgR) and Ki-67 labeling index may help in selecting patients with estrogen receptor-positive and HER2-negative tumors who can be spared or may benefit from the addition of chemotherapy to endocrine therapy. Guideline recommendations for an optimal testing of estrogen receptors and PgR have been issued to assist pathologists in the accurate assessment of these markers. Progress has also been made in the identification of candidate patients to HER2-targeted therapies and in the prediction of response to trastuzumab. Summary: Traditional molecular markers play a major role in the selection of candidate patients to systemic interventions, but they are of limited value in predicting their actual response to the different treatments, especially when the markers are evaluated individually
Design issues and performance analysis of CCM boost converters with RHP zero mitigation via inductor current sensing
No full textThe right-half plane (RHP) zero in the control to output voltage transfer function of a boost converter operating in the continuous conduction mode limits the loop bandwidth. By injecting a scaled version of the inductor current into the loop, it is possible to shift the zero from the right-half plane to the left-half plane, which leads to increased stability of the control loop. This solution generates a static voltage error at the output of the converter (tracking error), which may be unacceptable in practical applications. A few strategies to mitigate or correct this tracking error have been suggested. However, they have never been fully assessed. This paper thoroughly investigates the impact of the RHP zero mitigation technique on the dynamic performance of a boost converter, and identifies the complex trade-off between the system stability, transient response, and tracking error correction capability. Based on these findings, design guidelines are provided to help maximize system performance. A representative case study is considered to highlight the performance benefits and simulation results are presented to validate the analysis
Digital Auto-Tuning System For Inductor Current Sensing In VRM Applications
No full textInductor current sensing is becoming widely used in current programmed controllers for microprocessor applications. This method exploits a low-pass filter in parallel with the inductor to provide lossless current sense. A major drawback of inductor current sensing is that accurate sense the DC and AC components of the current signal requires precise matching between the low-pass filter time constant and the inductor time constant (L/RL). However, matching accuracy depends on the tolerance of the components and on the operating conditions; therefore it can hardly be guaranteed. To overcome this problem, a novel digital auto-tuning system is proposed that automatically compensates any time constant mismatch. This auto-tuning system has been developed for VRM current programmed controllers. It makes it possible to meet the adaptive voltage positioning requirements using conventional and low cost components, and to solve problems such as aging effects, temperature variations and process tolerances as well. A prototype of the auto-tuning system based on an FPGA and a commercial DC/DC controller has been designed and tested. The experimental results fully confirmed the effectiveness of the proposed method, showing an improvement of the current sense precision from about 30% up to 4%. This innovative solution is suitable to fulfill the challenging accuracy specifications required by the future VRM application
Mixed-Signal Voltage-Mode Control for DC DC Converters With Inherent Analog Derivative Action
No full textThis paper investigates a mixed-signal fixed frequency digital voltage-mode controller for dc-dc converters. Switch turn-on is determined by system clock, while switch turn-off is determined asynchronously by comparing a signal proportional to the derivative of the output voltage and the voltage ramp driven by the digital-to-analog converter (DAC). One of the most important features is that the derivative action of the proportional-integral-derivative (PID) voltage-mode controller is inherently obtained by a combination of the analog front-end and the hard-wired digital logic, without requiring the numerical computation of the derivative action nor analog reactive elements (capacitors), which are usually needed for the derivative action in the analog domain and which are critical for the IC controller integration. Moreover, as compared to conventional digital approaches based on analog-to-digital converters (ADCs) and digital pulsewidth modulators (DPWMs), the phase-lag due to the uniformly sampled DPWM and due to the output voltage sampling is avoided, thus improving phased margin at the crossover frequency where the derivative contribution is usually prevailing. This property potentially enables faster controllers with improved dynamic response, breaking bandwidth limitation of conventional digital control architectures. The proposed control architecture is also effective from the IC point of view, since it is based on a DAC, a simple analog front-end, including a sample and hold, a comparator and an operational amplifier, and low digital signal-processing requirement ( gates). Simulation and experimental results on a 1.2 V-20 A synchronous buck converter confirm the properties of the proposed solutio
Power Line Communication in Digitally Controlled DC–DC Converters Using Switching Frequency Modulation
No full textThis paper investigates power line communication (PLC) in digitally controlled high-frequency switched-mode power supplies in distributed architectures that share the same bus voltage. Communication between different DC-DC converters is obtained by using switching frequency modulation and by detecting the switching signal on the common supply bus voltage. In case of low power transmission, a small duty-cycle perturbation at half of switching frequency is added to enhance the energy of the transmitted signal. Each converter operates at three different switching frequencies: the first is associated with bit 1 transmission, the second is associated with bit 0 transmission, and the third is associated with no transmission state. In the proposed solution, there is no need for an additional power amplifier in order to inject the communication signal on the power lines, but the signal used for the PLC is inherently generated by the pulsewidth modulation of DC-DC converters. Even if aimed at a dedicated digital IC, the communication architecture has been implemented in field-programmable gate arrays. Simulation and experimental results on DC-DC synchronous buck converters confirm that the performance is achievable by the proposed PLC techniques
Novel control technique for single inductor multiple output converters operating in CCM with reduced cross-regulation
No full textAutotuning of Digitally Controlled DC–DC Converters Based on Relay Feedback
No full textThis paper proposes a simple autotuning technique for digitally controlled dc-dc converters. The proposed approach is based on the relay feedback method and introduces perturbations on the output voltage during converter soft-start. By using an iterative procedure, the tuning of proportional-integral-derivative parameters is obtained directly by including the controller in the relay feedback and by adjusting the controller parameters based on the specified phase margin and control loop bandwidth. A nice property of the proposed solution is that output voltage perturbations are introduced while maintaining the relay feedback control on the output voltage. The proposed algorithm is simple, requires small tuning times, and it is compliant with the cost/complexity constraints of integrated digital integrated circuits. Simulation and experimental results of a synchronous buck converter and of a dc-dc boost converter confirm the effectiveness of the proposed solutio
Synchronous Asynchronous Digital Voltage-mode control for DC-DC converters
No full textThis paper investigates a mixed synchronous/asynchronous digital voltage-mode controller for DC-DC converters. In the proposed control architecture, the turn-on switching event is determined asynchronously by comparing the converter output voltage and a synchronously generated voltage ramp driven by the digital control using a low-resolution digital-to-analog converter. Switch turn-off is determined synchronously by the system clock. In the proposed approach, the derivative action of the proportional-integral-derivative voltage-mode controller is inherently obtained by the frequency modulation, without requiring the digital computation of the derivative action. A simplified small-signal model is also derived in order to analyze the performance achievable by the proposed solution. This control architecture features good dynamic performance, and frequency modulation during transients. Simulation and experimental results on a synchronous buck converter, where the digital control has been implemented in field programmable gate array, confirm the effectiveness of the proposed solution
“Digital Controller for DC-DC Switching Converters”
No full textA voltage regulator includes an input terminal adapted for being coupled to an input voltage and an output terminal adapted for being coupled to a load. The voltage regulator includes a first switch adapted for selectively coupling to the input terminal and to the output terminal, a current sensor for measuring an output current flowing towards the output terminal, a voltage sensor for measuring the output voltage from the output terminal, and a digital controller which drives the first switch. The controller closes the first switch when the error voltage is less than a first preset value of voltage and opens the first switch when the output current is greater than a first preset value of current
High-Performance Mixed-Signal Voltage-Mode Control for dc-dc Converters with inherent analog derivative action
No full textThis paper investigates a mixed-signal fixed frequency digital voltage-mode controller for dc-dc converters. Switch turn-on is determined by system clock, while switch turn-off is determined asynchronously by comparing a signal proportional to the derivative of the output voltage and the voltage ramp driven by the Digital-to-Analog Converter (DAC). One of the most important features is that the derivative action of the Proportional-Integral-Derivative (PID) voltage-mode controller is inherently obtained by a combination of the analog front-end and the hard-wired digital logic, without requiring the digital computation of the derivative action nor any analog derivative circuits. This property potentially enables wide-bandwidth controllers with improvement in dynamic performance respect to conventional digital controllers based on Analog-to-Digital Converters (ADCs) and Digital Pulse Width Modulators (DPWMs). The proposed control architecture is also effective from the IC point of view, since it is based on a DAC, a simple analog front-end and low digital signal-processing requirement. Simulation and experimental results on a 1.2 V - 20 A synchronous buck converter confirm the validity of the proposed solution
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