Power amplifier protection by adaptive output power control

Abstract Cellular phone power amplifiers (PAs) operate in strongly varying environments and have to withstand extreme conditions. To avoid destructive breakdown a generic protection concept is proposed that is based on adaptive control of the output power. It provides over-voltage, over-temperature, and/or over-current protection by detection of the collector peak voltage, die temperature, and/or collector current to reduce the effective power control voltage once a threshold level is crossed. By applying protections, PAs can be implemented in low-cost silicon technology competitively to GaAs HBT implementations. In addition, requirements on package thermal resistance are relaxed. In this paper a theoretical analysis is given on the behavior of a class-AB amplifier under mismatch conditions. Measurement results on a silicon bipolar power transistor with integrated protection circuits are presented, proving the concept of adaptive protection. For a supply voltage of 5 V and nominal output power of 2 W no breakdown is observed for a VSWR of 10 over all phases when output power is adaptively reduced by 2.7 dB at most

Avalanche breakdown protection by adaptive output power control

Cellular phone power amplifier transistors, implemented in low-cost silicon technology, suffer from destructive breakdown. Their breakdown voltage is insufficient to withstand the high collector voltages that occur under extremes. To avoid breakdown an adaptive output power control concept is proposed that makes use of the detected collector peak voltage to limit the output power once a threshold level is crossed. Output power is limited by reducing the effective power control voltage. It avoids opposite actuation of the protection loop and that of the power control loop. For a supply voltage of 5 V and a nominal output power of 2 W no breakdown is observed for a VSWR of 10 over all phases

Power amplifier protection by adaptive output power control

Abstract Cellular phone power amplifiers (PAs) operate in strongly varying environments and have to withstand extreme conditions. To avoid destructive breakdown a generic protection concept is proposed that is based on adaptive control of the output power. It provides over-voltage, over-temperature, and/or over-current protection by detection of the collector peak voltage, die temperature, and/or collector current to reduce the effective power control voltage once a threshold level is crossed. By applying protections, PAs can be implemented in low-cost silicon technology competitively to GaAs HBT implementations. In addition, requirements on package thermal resistance are relaxed. In this paper a theoretical analysis is given on the behavior of a class-AB amplifier under mismatch conditions. Measurement results on a silicon bipolar power transistor with integrated protection circuits are presented, proving the concept of adaptive protection. For a supply voltage of 5 V and nominal output power of 2 W no breakdown is observed for a VSWR of 10 over all phases when output power is adaptively reduced by 2.7 dB at most

Adaptive Impedance-Matching Techniques for Controlling L Networks

The link quality of mobile phones suffers from antenna mismatch due to fluctuating body effects. Techniques for adaptive control of impedance-matching L networks are presented, which provide automatic compensation of antenna mismatch. To secure reliable convergence, a cascade of two control loops is proposed for independent control of the real and imaginary parts of impedance. A secondary feedback path is used to enforce operation into a stable region when needed. These techniques exploit the basic properties of tunable series and parallel LC networks. A generic quadrature detector that offers a power-independent orthogonal reading of the complex impedance value is presented, which is used for direct control of variable capacitors. This approach renders calibration and elaborate software computation superfluous and allows for autonomous operation of adaptive antenna-matching modules

A GSM/EDGE/WCDMA adaptive series-LC matching network using RF-MEMS switches

To preserve link quality of mobile phones, under fluctuating user conditions, an adaptively controlled series-LC matching circuit is presented for multi-band and multi-mode operation. Following a bottom-up approach, we discuss the design of an RF-MEMS unit cell for the construction of a 5-bit switched capacitor array. To reduce dielectric charging of the RF-MEMS devices their average biasing voltage is minimized by applying a bipolar waveform with a small high/low duty-cycle obtained from a high-voltage driver IC. RF-MEMS capacitive switches are applied because of their high linearity, low loss, large tuning range, and easy control in the discrete domain. Application specific RF-MEMS pull-in and pull-out voltage requirements are derived. An impedance phase detector is used to feed mismatch information to an up-down counter providing robust iterative control. The measured MEMS array capacitance tuning ratio is almost a factor 10. Module insertion loss is 0.5 dB at low-band and high-band. Harmonic distortion is less than -85 dBc at 35 dBm output power and the EVM, measured in EDGE-mode, is less than 1% at 27 dBm . The adaptively controlled module, connected to a planar inverted-F antenna, shows desired impedance correction. For extreme hand-effects the maximum module impedance correction at 900 MHz is -75jOmega

The hemodynamic effects of different pacing modalities after cardiopulmonary bypass in patients with reduced left ventricular function

Objectives: Patients with decreased left ventricular function undergoing cardiac surgery have a greater chance of difficult weaning from cardiopulmonary bypass and a poorer clinical outcome. Directly after weaning, interventricular dyssynchrony, paradoxical septal motion, and even temporary bundle-branch block might be observed. In this study, the authors measured arterial dP/dtmax, mean arterial pressure (MAP), and cardiac index using transpulmonary thermodilution, pulse contour analysis, and femoral artery catheter and compared the effects between right ventricular (A-RV) and biventricular (A-BiV) pacing on these parameters. Design: Prospective study. Setting: Single-center study. Participants: The study comprised 17 patients with a normal or prolonged QRS duration and a left ventricular ejection fraction ≤35% who underwent coronary artery bypass grafting with or without valve replacement. Interventions: Temporary pacing wires were placed on the right atrium and both ventricles. Different pacing modalities were used in a standardized order. Measurements and Main Results: A-BiV pacing compared with A-RV pacing demonstrated higher arterial dP/dtmax values (846 ± 646 mmHg/s v 800 ± 587 mmHg/s, p = 0.023) and higher MAP values (77 ± 19 mmHg v 71 ± 18 mmHg, p = 0.036). Conclusion: In patients with preoperative decreased left ventricular function undergoing coronary artery bypass grafting, A-BiV pacing improve the arterial dP/dtmax and MAP in patients with both normal and prolonged QRS duration compared with standard A-RV pacing. In addition, arterial dP/dtmax and MAP can be used to evaluate the effect of intraoperative pacing. In contrast to previous studies using more invasive techniques, transpulmonary thermodilution is easy to apply in the perioperative clinical setting

Effect of storage time of transfused plasma on early and late mortality after coronary artery bypass grafting

OBJECTIVES: Because some concern has been raised about the storage time of red blood cells and outcomes after cardiac surgery, we investigated whether longer storage time of transfused plasma increases the risk for early or late mortality among patients who have undergone coronary artery bypass grafting. METHODS: We retrospectively analyzed the data of all 10,626 patients who underwent isolated coronary artery bypass grafting in Catharina Hospital, Eindhoven, The Netherlands, between January 1998 and December 2007. All patients who received at least 1 unit of plasma intraoperatively or during the first 5 postoperative days were studied. They were divided into 3 groups (only younger plasma, only older plasma, and any older plasma groups) according to the storage time of the plasma (cutoff point, 323 days). RESULTS: After we had excluded 122 patients who were unavailable for follow-up, we found that 375 of the remaining patients (n = 745) received only younger plasma 370 patients received any older plasma, and 200 patients received only older plasma (mean follow-up, 1565 ± 1137 days; median follow-up, 1629 days). The storage time of plasma, when entered as either a continuous variable or a dichotomous variable, was a risk factor for early but not late mortality. Log-rank testing revealed no statistical difference in long-term survival among the groups. CONCLUSIONS: Longer storage time of plasma is a risk factor for early but not late mortality among patients who have undergone coronary artery bypass grafting

Ruggedness improvement by protection

Cellular phone power amplifier transistors have to withstand extreme voltages, temperatures and currents. Requirements on IC and packaging technology are relaxed by using over-voltage and over-temperature protection. To avoid breakdown, protection circuits are used that detect the collector peak voltage and die temperature to limit the output power once a threshold level is crossed. For a supply voltage of 5 V and a nominal output power of 2W, no breakdown is observed for a VSWR of 10 over all phases. For a VSWR of 4 and worst case mismatch phase the maximum die temperature is reduced from 143degC to 112degC when the output power is adaptively reduced from 32.1 dBm to 27.7 dB

RF-MEMS Based Adaptive Antenna Matching Module

To preserve the link quality, in fluctuating operating environments, an adaptive antenna matching module is presented that consists of a 5-bit RF-MEMS switched capacitor array, a bipolar 60/30 V MEMS-biasing voltage generator for improved reliability, and an impedance phase detector that provides information on mismatch. It uses an iterative up-down counting algorithm for robust control. Measurements show proper correction of the antenna reactance, even for a VSWR of 10. The switched capacitor array exhibits a large tuning range from 1 to 15 pF and an insertion loss of 0.4 dB. The detector dynamic range equals 35 dB with an accuracy of 8 degrees from 0.8 to 2 GHz. Adaptive matching will make isolators redundant