Introduction Anyone who has ever overseen the installation of a new cyclotron is aware of the importance of addressing the numerous vendor-supplied site specifications prior to its arrival. If the site is not adequately prepared, the facility may face project cost overruns, poor cyclotron performance and unintended maintenance costs. Once a facility has identified the space, providing sufficient power is the next step. Every cyclotron vendor will provide you with a set of power specifications, but meeting these specifications can be difficult, especially when the cyclotron is placed in an existing structure. The cyclotron is an interesting collection of power supplies providing power to sensitive electronic circuitry. It is not sufficient to just provide enough power; you must also provide quality power. It is hoped that our efforts to resolve our poor power quality problems will assist others as they replace aging cyclotrons in existing institutions whose power quality has degraded over the years. The University of Iowa Hospitals and Clinics completed installation of a GE PETtrace 800 cyclotron in November 2011. Four months prior to installation, GE service personnel arrived to do a power assessment. The result was that we met their specifications, but with reservations. We could easily provide the quantity of power required, but the specification also states that GE recommends that primary power remain at 480 VAC ± 5%. GE service personnel attached a power quality analyzer to the cyclotron main power panel and determined that we did have some events of 7 to 8 % sag, but they were in-frequent, perhaps once or twice a week lasting 20 to 50 msec. Sags were confirmed to be the result of large non-linear loads elsewhere in the hospital. If these occurred during a run, they may shut down the cyclotron, specifically the RF power supply. Further investigation revealed the presence of harmonics on our power. Harmonics are the multiples of 60Hz power that are reflected back into your facility’s power grid from large motor drivers. Commercial air handler, water pump and fan motors often use variable frequency drives (VFDs) for proportional control to meet the changing facility demands. This pro-vides a significant on-going cost savings, but may play havoc with power quality throughout the institution. Harmonic distortion is often quantified as a total harmonic distortion (THD) percentage. Though not specifically mentioned in the site-specifications, our experience here will show that it is important not to overlook harmonic distortion. Its effects can be varied, erratic and wide-spread throughout the cyclotron system. When asked, GE service referred us to IEEE standards for electrical systems and equipment which states that THD is recommended to be below 5 % for most applications, but below 3 % for sensitive settings including airports and hos-pitals1. Mitigation of voltage sag and harmonic distortion is an expensive and complex topic. It is recommended that you consult with your cyclotron vendor to determine if there exists a field-tested solution. Additionally, you should consult a power systems specialist to do an audit of your building’s power system. Material and Methods Characterization of Power Quality: This was accomplished using a Hioki 3197 Power Quality Analyzer and a couple Dranetz PX-5 Power Xplorers. Each monitoring cycle logged data for about a week, which seemed to be about the limit for these units when logging both THD and surge/sag events down to the duration of a single 60Hz cycle. Analysis of the circuit diagrams and communication with GE engineers indicated that the main power contactors to the cyclotron RF system were dropping power to protect the system. The feedback for this shutoff is a detection signal from the front-end EHT (high-voltage generation) circuit that is set at a level to be representative of the 5% AC deviation specification. RF Power System Contactors: Every time the contactors of the RF power distribution system are energized/de-energized, some arching occurs at the contact surfaces. This arching pits the contactor surfaces such that over time the contactor surfaces become irregular and potentially resistive. Since the RF protection circuit triggered by the EHT circuit is downstream from the contactors, it is not so hard to envision why the system becomes more sensitive over time2. Additionally, the harmonic distortion also exists on the AC voltage energizing the contactors. As a result, they may not actuate as smoothly (de-pendent of degree of harmonic distortion) and further hasten the normal rate of pitting of contactor surfaces. Results and Conclusion Within weeks of installation, we began to get RF power shutoffs. They were infrequent at first, but soon began to occur numerous times a week, then numerous times a day. At approximately 3 months post installation, it was often difficult to get through a standard 30 to 45 minute bombardment to make F-18 for our daily patient FDG doses. We limped along for over a year until the University was willing to invest in a solution to address our power problems. Periodic Power Analyses: These analyses, per-formed over the next year, indicated that our power quality worsened in the winter and re-turned to functional levels in the summer. The instance of voltage sag remained approximately the same throughout the year (a few short sags per week), but the THD was down to 6 % in the summer and nearly 10% in the winter. This result, combined with RF shutdown tracking and lack of correlation between observed power sags and RF shutdowns, led us to the conclusion that our very high harmonic distortion combined with small power fluctuations (< 5 %) were the culprit. Mitigation Planning: There are a number of power conditioning technologies, but imposing the need to remove both voltage sag as well as harmonic distortion, quickly narrows the field. What remains are the following options: 1) UPS line conditioner with batteries, 2) UPS line conditioner with flywheel or 3) motor-generator power isolator. Battery maintenance costs ruled out the UPS battery line conditioner. Of the remaining two, if you have the space, the motor-generator is the simplest and cheapest (favored by forward military hospital units). But for the space constrained user, like us, the UPS flywheel line conditioner became the preferred option. Additionally, it was identified in a power audit that the THD was only 4% at the transformers connected directly to the local power utility company supply (upstream of load effect and harmonic distortion sources). This was to be expected as load effects and harmonic distortion are worse if your tie-in point to the building power grid is at the same level or downstream of their sources. Additionally, a test was performed during a hospital backup generator test, wherein the suspected primary offenders (large motors and VFDs) were diverted to backup. As a result, the THD measured at the cyclotron primary power panel dropped by 2.5 %. Working with University electricians, an outside power consultant, GE engineering and University Hospital Radiology Engineering, a two phase plan was created. Phase 1: With a repurposed utility transformer, the cyclotron and PET cameras got their own dedicated transformer connected to the main utility power feed. We also replaced the old contactors in the RF power distribution system. Since installation, the measured THD has remained at 4.5 to 5 % year round and the sag incidence and magnitude are slightly improved. Phase 2: With a quote from GE for a flywheel UPS we should be able to fully condition the power entering our facility, removing the load effect voltage sags as well as the harmonic distortion. One year of operation after Phase 1 implementation, it has been decided that Phase 1 was all that was required. We haven’t had a single new instance of RF shutdown since.

<p>Measurements are important to specify and verify properties for components, modules and systems. The specifications for a certain figure of merit are usually given in a numerical value or a two dimensional plot. However, there are some devices, like power amplifiers with certain figure of merits that depends on two or more working conditions, requiring a three dimensional plot.</p><p>This thesis presents a measurement method including graphical user interface of three parameters gain, efficiency and distortion when two-tone or WCDMA signals are used as an input to the PA.</p>

Measurements are important to specify and verify properties for components, modules and systems. The specifications for a certain figure of merit are usually given in a numerical value or a two dimensional plot. However, there are some devices, like power amplifiers with certain figure of merits that depends on two or more working conditions, requiring a three dimensional plot. This thesis presents a measurement method including graphical user interface of three parameters gain, efficiency and distortion when two-tone or WCDMA signals are used as an input to the PA.

The FREIA laboratory is a Facility for REsearch Instrumentation and Acceleratior development at Uppsala University, Sweden, constructed recently to test and develop superconducting accelerating cavities and their high power RF sources. FREIA's activity target initially the European Spallation Source (ESS) requirements for testing spoke cavities and RF power stations, typically 400 kW per cavity. Different power stations will be installed at the FREIA laboratory. The first one is based on vacuum tubes and the second on a combination of solid state modules. In this context, we investigate different related aspects, such as power generation and power combination. For the characterization of solid state amplifier modules in pulsed mode, at ESS specifications, we implement a Hot Sparameter measurement set-up, allowing in addition the measurement of different parameters such as gain and efficiency. Two new solid state amplifier modules are designed, constructed and measured at 352 MHz, using commercially available LDMOS transistors. Preliminary results show a drain efficiency of 71 % at 1300 W pulsed output power. The effects of changing quiescent current (IDq) and drain voltage are investigated, aswell as the possibilities to combine several modules together.

This thesis presents a high efficiency RF to DC converter for RFID applications. The proposed circuit has been designed in 90 nm CMOS technology using a single RF source. It exploits an internal Vth cancellation technique along with a leakage current reducer. The circuit operates in two phases: Phase 1, applies a DC voltage between gate and drain to reduce the VDS of the PMOS transistor; and Phase 2 removes this DC voltage meanwhile by pulling the drain and source terminals of the same transistor to the same potential, reducing the sub-threshold leakage current and enhancing the power conversion efficiency. The simulation results show that high DC power up to 8.1µA can be delivered to the load. The PCE has been measured 36.3% at -14.3dBm and can be improved to 54.5% providing an impedance matching network between the source and rectifier input.

No description available.

Introduction Anyone who has ever overseen the installation of a new cyclotron is aware of the importance of addressing the numerous vendor-supplied site specifications prior to its arrival. If the site is not adequately prepared, the facility may face project cost overruns, poor cyclotron performance and unintended maintenance costs. Once a facility has identified the space, providing sufficient power is the next step. Every cyclotron vendor will provide you with a set of power specifications, but meeting these specifications can be difficult, especially when the cyclotron is placed in an existing structure. The cyclotron is an interesting collection of power supplies providing power to sensitive electronic circuitry. It is not sufficient to just provide enough power; you must also provide quality power. It is hoped that our efforts to resolve our poor power quality problems will assist others as they replace aging cyclotrons in existing institutions whose power quality has degraded over the years. The University of Iowa Hospitals and Clinics completed installation of a GE PETtrace 800 cyclotron in November 2011. Four months prior to installation, GE service personnel arrived to do a power assessment. The result was that we met their specifications, but with reservations. We could easily provide the quantity of power required, but the specification also states that GE recommends that primary power remain at 480 VAC ± 5%. GE service personnel attached a power quality analyzer to the cyclotron main power panel and determined that we did have some events of 7 to 8 % sag, but they were in-frequent, perhaps once or twice a week lasting 20 to 50 msec. Sags were confirmed to be the result of large non-linear loads elsewhere in the hospital. If these occurred during a run, they may shut down the cyclotron, specifically the RF power supply. Further investigation revealed the presence of harmonics on our power. Harmonics are the multiples of 60Hz power that are reflected back into your facility’s power grid from large motor drivers. Commercial air handler, water pump and fan motors often use variable frequency drives (VFDs) for proportional control to meet the changing facility demands. This pro-vides a significant on-going cost savings, but may play havoc with power quality throughout the institution. Harmonic distortion is often quantified as a total harmonic distortion (THD) percentage. Though not specifically mentioned in the site-specifications, our experience here will show that it is important not to overlook harmonic distortion. Its effects can be varied, erratic and wide-spread throughout the cyclotron system. When asked, GE service referred us to IEEE standards for electrical systems and equipment which states that THD is recommended to be below 5 % for most applications, but below 3 % for sensitive settings including airports and hos-pitals1. Mitigation of voltage sag and harmonic distortion is an expensive and complex topic. It is recommended that you consult with your cyclotron vendor to determine if there exists a field-tested solution. Additionally, you should consult a power systems specialist to do an audit of your building’s power system. Material and Methods Characterization of Power Quality: This was accomplished using a Hioki 3197 Power Quality Analyzer and a couple Dranetz PX-5 Power Xplorers. Each monitoring cycle logged data for about a week, which seemed to be about the limit for these units when logging both THD and surge/sag events down to the duration of a single 60Hz cycle. Analysis of the circuit diagrams and communication with GE engineers indicated that the main power contactors to the cyclotron RF system were dropping power to protect the system. The feedback for this shutoff is a detection signal from the front-end EHT (high-voltage generation) circuit that is set at a level to be representative of the 5% AC deviation specification. RF Power System Contactors: Every time the contactors of the RF power distribution system are energized/de-energized, some arching occurs at the contact surfaces. This arching pits the contactor surfaces such that over time the contactor surfaces become irregular and potentially resistive. Since the RF protection circuit triggered by the EHT circuit is downstream from the contactors, it is not so hard to envision why the system becomes more sensitive over time2. Additionally, the harmonic distortion also exists on the AC voltage energizing the contactors. As a result, they may not actuate as smoothly (de-pendent of degree of harmonic distortion) and further hasten the normal rate of pitting of contactor surfaces. Results and Conclusion Within weeks of installation, we began to get RF power shutoffs. They were infrequent at first, but soon began to occur numerous times a week, then numerous times a day. At approximately 3 months post installation, it was often difficult to get through a standard 30 to 45 minute bombardment to make F-18 for our daily patient FDG doses. We limped along for over a year until the University was willing to invest in a solution to address our power problems. Periodic Power Analyses: These analyses, per-formed over the next year, indicated that our power quality worsened in the winter and re-turned to functional levels in the summer. The instance of voltage sag remained approximately the same throughout the year (a few short sags per week), but the THD was down to 6 % in the summer and nearly 10% in the winter. This result, combined with RF shutdown tracking and lack of correlation between observed power sags and RF shutdowns, led us to the conclusion that our very high harmonic distortion combined with small power fluctuations (< 5 %) were the culprit. Mitigation Planning: There are a number of power conditioning technologies, but imposing the need to remove both voltage sag as well as harmonic distortion, quickly narrows the field. What remains are the following options: 1) UPS line conditioner with batteries, 2) UPS line conditioner with flywheel or 3) motor-generator power isolator. Battery maintenance costs ruled out the UPS battery line conditioner. Of the remaining two, if you have the space, the motor-generator is the simplest and cheapest (favored by forward military hospital units). But for the space constrained user, like us, the UPS flywheel line conditioner became the preferred option. Additionally, it was identified in a power audit that the THD was only 4% at the transformers connected directly to the local power utility company supply (upstream of load effect and harmonic distortion sources). This was to be expected as load effects and harmonic distortion are worse if your tie-in point to the building power grid is at the same level or downstream of their sources. Additionally, a test was performed during a hospital backup generator test, wherein the suspected primary offenders (large motors and VFDs) were diverted to backup. As a result, the THD measured at the cyclotron primary power panel dropped by 2.5 %. Working with University electricians, an outside power consultant, GE engineering and University Hospital Radiology Engineering, a two phase plan was created. Phase 1: With a repurposed utility transformer, the cyclotron and PET cameras got their own dedicated transformer connected to the main utility power feed. We also replaced the old contactors in the RF power distribution system. Since installation, the measured THD has remained at 4.5 to 5 % year round and the sag incidence and magnitude are slightly improved. Phase 2: With a quote from GE for a flywheel UPS we should be able to fully condition the power entering our facility, removing the load effect voltage sags as well as the harmonic distortion. One year of operation after Phase 1 implementation, it has been decided that Phase 1 was all that was required. We haven’t had a single new instance of RF shutdown since.

<p>To obtain the power levels required from high RF power transistors, the size of the chip has often to be made so large that inductance of electrical connections inside the package cannot be neglected. This may have the effect that various parts of the transistor chip are not connected exactly parallel, i.e. drain and gate voltages and currents densities will not be the same on different parts of the chip. This may result in degraded output power and efficiency. The same effect may occur when more than one chip are connected in parallel in a transistor package to obtain even higher output power.Often the connections to the transistor package are approximated as a number of electrical point connections (normally three: gate, drain, source); meaning that each of them can be described by a single electrical potential and current. In reality, they may be large enough that voltage and current distributions have to be considered. These distributions will be affected by different mountings of the transistor and other connected components.In this work, the LDMOS power transistor MRF6S21140HR3 was modeled using the segmentation method in high frequency signal simulation HFSS which is a 3D Full-Wave Electromagnetic Field Simulation, and utilized the advanced design system ADS to find a parameterized lumped model. Both the electromagnetic and lumped models showed consistent results. Non-ideal parallel connection of sub-transistors on chip is very important, but further studies are needed for definite conclusion. It was verified through modeling that non ideal parallel connection of different chips in the package does have an effect; the effect however is quiet small which proves that the signal is slightly non-uniformly distributed between the three chips in the package. External connection to PCB (drain connection is considered in this work) can effectively be taken as a point connection to some approximation. The electrical behavior of the modeled transistor was studied through the design of a class B power amplifier in order to estimate the importance of performance degradation due to non-ideal parallel connections and how these non ideal connections degrade efficiency and output power. The modeled transistor can deliver a maximum output power of 147 watts and efficiency of 65%. We have also studied the current distribution between the three chips in a three stage class B power amplifier. Again, the difference in the current distribution between the three chips turned out to be quiet small. All these results are presented through this work. The final conclusion regarding the current distribution between multichips cannot be made just based on these simulation results. The next step should be aimed at considering other effects, the thermal effect for example, in order to know exactly whether it is uniformly or not uniformly distributed.</p>

To obtain the power levels required from high RF power transistors, the size of the chip has often to be made so large that inductance of electrical connections inside the package cannot be neglected. This may have the effect that various parts of the transistor chip are not connected exactly parallel, i.e. drain and gate voltages and currents densities will not be the same on different parts of the chip. This may result in degraded output power and efficiency. The same effect may occur when more than one chip are connected in parallel in a transistor package to obtain even higher output power.Often the connections to the transistor package are approximated as a number of electrical point connections (normally three: gate, drain, source); meaning that each of them can be described by a single electrical potential and current. In reality, they may be large enough that voltage and current distributions have to be considered. These distributions will be affected by different mountings of the transistor and other connected components.In this work, the LDMOS power transistor MRF6S21140HR3 was modeled using the segmentation method in high frequency signal simulation HFSS which is a 3D Full-Wave Electromagnetic Field Simulation, and utilized the advanced design system ADS to find a parameterized lumped model. Both the electromagnetic and lumped models showed consistent results. Non-ideal parallel connection of sub-transistors on chip is very important, but further studies are needed for definite conclusion. It was verified through modeling that non ideal parallel connection of different chips in the package does have an effect; the effect however is quiet small which proves that the signal is slightly non-uniformly distributed between the three chips in the package. External connection to PCB (drain connection is considered in this work) can effectively be taken as a point connection to some approximation. The electrical behavior of the modeled transistor was studied through the design of a class B power amplifier in order to estimate the importance of performance degradation due to non-ideal parallel connections and how these non ideal connections degrade efficiency and output power. The modeled transistor can deliver a maximum output power of 147 watts and efficiency of 65%. We have also studied the current distribution between the three chips in a three stage class B power amplifier. Again, the difference in the current distribution between the three chips turned out to be quiet small. All these results are presented through this work. The final conclusion regarding the current distribution between multichips cannot be made just based on these simulation results. The next step should be aimed at considering other effects, the thermal effect for example, in order to know exactly whether it is uniformly or not uniformly distributed.

No description available.