The growing interest for high data rate wireless communications over the last few decades
gave rise to the emergence of a number of wideband wireless systems. The resulting scarcity
of frequency spectrum has been forcing wireless system designers to develop methods that
will push the spectral efficiency to its limit.
Rapid growth of wireless communication services in recent decades has created
a huge demand of radio spectrum. Spectrum scarcity and utilization inefficiency
limit the development of wireless networks. Cognitive radio is a promising tech-
nology that allows secondary users to reuse the underutilized licensed spectrum of
primary users. The major challenge for spectrum sharing is to achieve high spectrum
efficiency while making non-intrusive access to the licensed bands. This requires in-
formation of availability and quality of channel resources at secondary transmitters,
however, is difficult to be obtained perfectly in practice.
One of the prerequisites for the development of telecommunication services is the
understanding of the propagation of the waves, either acoustic, electromagnetic,
radio or light waves, which are used for the transmission of information.
In this work, we shall limit ourselves to the study of radio waves: this term
apply to the electromagnetic waves used in radio communications. Their
frequency spectrum is very broad, and is divided into the following frequency
bands : ELF waves (f < 3 kHz), VLF (3-30 kHz), LF waves (30-300 kHz), MF
waves (300-3000 kHz), HF (3-30 MHz), VHF waves (30-300 MHz), UHF waves
(300-3000 MHz), SHF waves (3-30 GHz), EHF waves (30-300 GHz) and sub-
EHF waves (300-3000 GHz).
The mature CMOS fabrication processes are available
in many IC foundries. It is cost-effective to leverage the
existing CMOS fabrication technologies to implement
MEMS devices. On the other hand, the MEMS devices
could also add values to the IC industry as the Moore’s law
reaching its limit. The CMOS MEMS could play a key role
to bridge the gap between the CMOS and MEMS
technologies. The CMOS MEMS also offers the advantage
of monolithic integration of ICs and micro mechanical
components.
The continuous progress in modern power device technology is increasingly
supported by power-specific modeling methodologies and dedicated simulation
tools. These enable the detailed analysis of operational principles on the the device
and on the system level; in particular, they allow the designer to perform trade-
off studies by investigating the operation of competing design variants in a very
early stage of the development process. Furthermore, using predictive computer
simulation makes it possible to analyze the device and system behavior not only
under regularoperatingconditions, but also at the rim of the safe-operatingarea and
beyond of it, where destructive processes occur that limit the lifetime of a power
system.
2.7V to 5.5V input voltage Range? Efficiency up to 96%
? 24V Boost converter with 12A switch
current limit? 600KHz fixed Switching Frequency? Integrated soft-start? Thermal Shutdown? Under voltage Lockout? Support external LDO auxiliary power
supply? 8-Pin SOP-PP PackageAPPLICATIONSPortable Audio Amplifier Power SupplyPower BankQC 2.0/Type CWireless ChargerPOS Printer Power SupplySmall Motor Power Supply
The PW4055 is a complete constant-current /constant-voltage linear charger for single cell lithiumion batteries.Its ThinSOT package and low external component count make the PW4055 ideallysuited for portable applications.Furthermore, the PW4055 is specifically designed to work within USBpower specifications.The PW4055 No external sense resistor is needed, and no blocking diode is required due to theinternal MOSFET architecture.Thermal feedback regulates the charge current to limit the dietemperature during high power operation or high ambient temperature. The charge voltage is fixedat 4.2V, and the charge current can be programmed externally with a single resistor. The PW4055automatically terminates the charge cycle when the charge current drops to 1/10th the programmedvalue after the final float voltage is reached. When the input supply (wall adapter or USB supply) isremoved, the PW4055 automatically enters a low current state, dropping the battery drain currentto less than 2μA. The PW4055 can be put into shutdown mode, reducing the supply current to 25μA.The BAT pin has a 7KV ESD(HBM) capability. Other features include charge current monitor, undervoltage lockout, automatic recharge and a status pin to indicate charge termination and the presenceof an input voltage
PW1555 is a programmable current limit switch with input voltage range selection and outputvoltage clamping. Extremely low RDS(ON) of the integrated protection N-channel FET helps toreduce power loss during the normal operation. Programmable soft-start time controls the slew rateof the output voltage during the start-up time. Independent enable control allows the complicatedsystem sequencing control. It integrates the over-temperature protection shutdown andautorecovery with hystersis
設計了農(nóng)業(yè)溫濕度智能控制系統(tǒng),該系統(tǒng)采用DHT11溫濕度傳感器作為溫濕度采集模塊,單片機選用AT89C52代替并調(diào)用Virtual terminal模擬串口通信,LCD1604液晶顯示器實時顯示溫濕度,實現(xiàn)了溫濕度的測量、顯示,可自動控制加熱、降溫、加濕、通風,實現(xiàn)溫濕度控制以及超限報警處理,并利用Proteus與Keil進行實際電路的仿真。試驗表明,該系統(tǒng)實現(xiàn)了可靠的溫濕度監(jiān)控。We described the design of an intelligent control system of agriculture temperature and humidity.The system uses DHT11 temperature and humidity sensor as the temperature and humidity acquisition module.The SCM adopts AT89C52 to replace and call the virtual terminal for simulating serial communication.LCD1604 displays temperature and humidity in real time,which implements the measurement and display of temperature and humidity.The system is able to automatically control heating,cooling,humidification and ventilation,to achieve temperature and humidity control and over-limit alarm processing.The system also uses Proteus and Keil for actual circuit simulation.The experiment shows that the system is capable of reliable temperature and humidity monitoring.
