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BLL6H1214L(S)-250 Datasheet(PDF) 62 Page - NXP Semiconductors |
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BLL6H1214L(S)-250 Datasheet(HTML) 62 Page - NXP Semiconductors |
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62 / 130 page -250/4334/62/BLL6H1214L(S)-250.png) 63 NXP Semiconductors RF Manual 16th edition RF radiation is not a new technology in medicine. It is currently used for imaging purposes in MRI (magnetic resonance imaging) and EPRI (electron paramagnetic resonance imaging), techniques that employ frequencies from a few megahertz to about 500 MHz. Other well-known external heat-treatments to rejuvenate skin or relieve muscle pain make use of frequencies around 480 kHz – not too demanding in terms of RF. Surgical equipment to cut and simultaneously coagulate blood vessels runs off RF at about 5 MHz. The latter application belongs to a class of treatment techniques that is growing rapidly and uses RF radiation to deposit energy locally at various parts of the body – in general to “ablate” (remove) unwanted tissue. Inside the body, the RF energy heats the surrounding tissue until it is desiccated and/or necrotized. The damaged tissue will later be re-absorbed by the surrounding, living tissue. Further application examples for RF ablation include cancer treatment in the lung, kidney, breast, bone and liver, removal of varicose veins, treatment of heart arrhythmia, and a growing list of other applications that benefit from the high control and feedback possible with RF. Another advantage of RF in this context is the fact that it can be applied via small catheters ending in antennas that deploy the RF signal. Unlike older, direct-current techniques, the tissue is heated only very locally around the antenna. Neighboring nerves (and the heart) are not stimulated. This led to the development of a variety of specialized catheters, used during minimally invasive surgery, along with ultrasound or X-ray imaging to determine the exact location of the RF-active part. During the treatment, the impedance of the surrounding tissue can be monitored and the end-point determined. With proper catheters, one can even achieve “self limitation” due to the reduced uptake of RF energy in desiccated tissue. Likewise, the RF frequency can be used to tune the energy deposition zone around the catheter: the higher the frequency, the smaller the penetration depth – and hence the volume to deposit the RF energy – in the watery tissue. With the trend towards higher RF frequencies and powers, the complexity of RF generators and the requirements for the device technology also increase. Above 10 MHz, say, up to 3.8 GHz, the technology of choice for power amplifiers is Si LDMOS (laterally 2.5Industrial,scientific&medical 2.5.1 MedicalapplicationsdrivenbyRFpower:Fromimagingtocancertreatment, aflexibleandversatiletechnologyinthedoctor’stoolbox diffused metal oxide semiconductor). This technology has proven to be powerful, efficient, and rugged in base stations, radar systems, broadcast transmitters, and other industrial, scientific, and medical (ISM) applications. LDMOS is available from up to 50 V supply to achieve power levels up to 1,200 W per single device, with outstanding ruggedness and high gain and efficiency. To drive and control the LDMOS power amplifier stages, it takes voltage-controlled oscillators, phase locked loops, and medium power amplifiers. These parts of the RF signal chain are conveniently available based on reliable and high-volume SiGe:C (QUBiC) semiconductor technologies. Going a step further, one can even use high-speed converters to drive the signal chain entirely from the digital domain, for full and easy control over the shape and modulation of the applied RF. RF implications These in-situ medical applications and, in general, most of the ISM applications, usually form highly mismatched RF loads during some part of the usage cycle. This in turn means that, without protection or other measures, all of the "injected" RF power reflects back into the final stage of the amplifier and needs to be dissipated in the transistor(s), and most likely destroys the device(s) if this situation lasts too long. LDMOS transistors are designed to be extremely rugged and generally withstand these mismatch situations without degrading over time. This device ruggedness, or the ability to withstand “harsh” RF conditions in general, be it mismatch or extremely short pulse rise and fall times, is essential for reliable device performance. RF power companies have gone to great lengths to achieve best-in-class device ruggedness. The technologies have been hardened under the most stringent ruggedness tests during development, which is particularly true for the 50 V technology. Among other factors, the base resistance of the parasitic bipolar and the drain extension of the LDMOS device play key roles in this respect. This ruggedness, combined with the power density and the high efficiencies achievable, make LDMOS the preferred technology for RF power amplifiers up to 3.8 GHz. RF technology is making its way into all kinds of medical applications, ranging from the well-known imaging techniques (MRI, EPRI) over low frequency, external heat treatment, and electro-surgical tools, to minimally invasive endoscopic cancer treatment (RF ablation). One clear trend is the increasing share of RF-based technologies for ablation. Another is the trend towards higher RF frequencies (several GHz) and higher powers (> 100 W) in order to achieve higher spatial resolution, better control, and shorter treatment times. |
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