Wireless sensor networks (Wireless Sensor Networks, WSN) were originally developed for military applications and are now widely used in many other fields such as industrial process monitoring, environmental monitoring, smart building and home automation (Home automaTIon) etc. Scalability, low power consumption, reduced construction costs, small size, and redundant functions are some of the key features that drive wireless sensor network applications. A typical wireless sensor network consists of three main parts: multiple sensor nodes, a gateway, and software used for communication (as shown in Figure 1). The sensor node is powered by a small battery, using energy recovery (such as solar energy) technology or connected to a main power supply. The limitation of energy sources poses significant challenges to the signal path and power management of sensor nodes. National Semiconductor has developed high-efficiency power conversion and sensor signal mediation solutions to help provide the latest functions for sensor nodes and ensure stable operation.
Sensor nodes have a wide range of applications, ranging from the use of sensors to detect temperature, dynamics and pressure in home and building applications to the monitoring of toxic gas concentrations such as CO, CO2, NO2 or CH4. The sensor node hardware block diagram is basically very similar as a standalone application. It is composed of sensors, analog sensor signal mediation, radio transceivers, embedded processors, and energy sources for the entire node. (as shown in picture 2). Since most sensor nodes are powered by batteries or energy recovery technologies, low system power consumption is a key requirement for successful design. Radio transmission and microprocessor data acquisition are usually the largest sources of energy available. Low data rates and short-range communication duration keep these components in low-power standby or idle mode most of the time. To ensure the longest battery life and system stability, many manufacturers have designed processors specifically for these ultra-low power applications. The remaining energy can be used for the analog signal adjustment of the sensor output.
The low-power, high-performance analog technology developed by National Semiconductor can respond to sensor signal mediation and sensor node power management challenges. National Semiconductor's LPV521 micropower amplifier provides the required sensor output signal amplification function for an analog-to-digital converter (ADC) connected to an embedded microcontroller. In addition to ultra-low power consumption, the electromagnetic interference (EMI) protection design is also used in the LPV521 component to reduce the radio frequency communication sensitivity from wireless sensor network radio. In addition, National Semiconductor recently introduced the LMP91000 programmable analog front end (AFE) for electrochemical sensing applications (such as toxic gas detection). The LMP91000 provides a complete signal path solution between the sensor and the microcontroller, which can produce an output voltage proportional to the battery current. The programmability of the LMP91000 can support multiple electrochemical sensors using only one design instead of multiple discrete components.
Each analog and digital load at the sensor node has its own power supply considerations. Both the analog signal path and the RF circuit require a low noise power supply with high power supply rejection ratio (PSRR) to ensure the highest performance. The low dropout voltage regulator (LDO) of National Semiconductor LP5900 provides a good choice for low noise power supply for sensitive analog circuits. The embedded microcontroller needs a power supply with good overall efficiency and fast response time to support the wake-up and sleep cycles of the sensor network. A regulator or low dropout regulator with excellent light load efficiency is a suitable choice. Nodes powered by batteries or energy recovery technologies still have a limiting factor due to limited energy recovery, requiring the use of ultra-low quiescent current regulators to maximize the running time of sensor nodes. The LM2936 and LP3869x of the National Semiconductor low-dropout voltage regulator series can operate under low quiescent current conditions and have fast response times required by embedded processors with sensor nodes. The LM2936 also has a wide input voltage range up to 40V, which is derived from the AC / DC rectified power supply used in the sensor node. National Semiconductor's low-noise, high-accuracy voltage references (such as LM4140) are ideal for data conversion designs that require high accuracy. Since the gateway of the wireless sensor network usually does not have a limited energy source, the design of the power supply can be more flexible. National Semiconductor's SIMPLE SWITCHER voltage regulators and modules (such as LM2267x and LMZ1200x) provide easy-to-use point-of-load power supply solutions for gateway applications, while having the added advantage of ultra-low radiation EMI performance. Overall, National Semiconductor has a complete and diverse power management solution that can meet the various requirements of wireless sensor network applications.
National Semiconductor has many easy-to-use WEBENCH sensor design tools and WEBENCH sensor sensing analog front-ends to help designers easily and quickly design and simulate analog sensor signal mediation solutions for applications including pressure and temperature , Load and gas and other common sensors. WEBENCH Power Design Tool is another resource for creating complete DC / DC power supply designs that can optimize efficiency, size, and cost.
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