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CC2531 and CC2591 SoC Chip Based on the WSN node communication module

In Electronic Infomation Category: C | on April 19,2011

Wireless sensor network (Wireless Sensor Network, WSN) for its low complexity, low-cost, low power, multi-network nodes, etc., in real life more and LT1057IS8 datasheet and more widely, especially in some System on Chip (SoC ) The emergence of wireless sensor network greatly reduces the development effort. In the application of these systems on-chip wireless sensor network development, due to on-chip wireless communication system itself is very small part of the transmission power (such as CC2531 transmitter power is only 4.5 dBm), together with its receiver sensitivity is also fixed at a certain level This limits the communication range of wireless sensor networks, common transmission distance of a few hundred meters. In some specific applications, the requirements placed between network nodes to one kilometer or more away from even farther.

This paper describes a core chip CC2531-based wireless sensor network node design, application 2.4 GHz TIs CC2591 RF front-end chips to enhance the wireless communication part of the transmission power, to further improve the receiver sensitivity, thus extending the communication distance .

1 core chip introduction

1.1 CC2531

CC2531 is TI has introduced a USB function for IEEE 802.15.4, ZigBee and LT1057IS8 price and system on chip applications RF4CE (SoC) solutions. It can be a very low total cost of materials to build a strong network nodes. CC2531 integrates a 2.4 G. Hz of the RF transceiver, industry-standard enhanced 8051 MCU, in-system programmable in 256 KB Flash, 8 KB RAM and LT1057IS8 suppliers and many other powerful features; emission power 4.5 dBm (adjustable), receiver sensitivity of the receiver -97 dBm.

1.2 CC2591

CC2591 is TI introduced the work in the 2.4 GHz, for low power consumption and low voltage wireless applications, highly integrated RF front-end chip. CC2591s internal integrated power amplifier (PA) of the gain is 22 dB, maximum transmit power of +22 dBm (input +5 dBm), the output 1 dB compression point of +19 dBm, to receive some level of internal integration of the LNA to receive gains of sub- 11 dBm, 1 dBm, noise figure of 4.8 dB, receiver sensitivity improvement of 6 dB.

2 overall design

According to design requirements, system hardware block diagram shown in Figure 1. Core chip CC2531 combined with its peripheral circuits (such as crystal, A / D reference voltage, memory, sensors, and debug interface, etc.), plus the necessary power supply module and the RF front-end chip, CC2591, constitute the hardware of the program. When applied to different areas, the corresponding sensors, power supply, A / D reference voltage, memory, etc. can be adjusted accordingly. CC2531 and CC2591 part of the hardware design is relatively fixed.


Figure 1 System hardware block diagram

3 performance parameters budget

3.1 transmitter power budget According to CC2531 and CC2591

data sheet shows: CC2531RF port maximum transmission power +4.5 dBm, the value of the register can be modified TXPOWER adjust its transmission power, the range of -22 ~ +4.5 dBm. After connecting CC2591, CC2591 transmit mode PA gain maximum 22 dB, the corresponding transmission power range of +22 ~ 10 dBm (the maximum value determined by the PA itself, the minimum can be smaller.) Considering the PA of 1 dBm compression point (19 dBm) and power consumption and other factors, to set the TX-POWER = 0xD5, the CC2531 output power of 1 dBm, CC2591 19 dBm transmit power is ideal for the large power output reference set (for reference only, the actual change may be).

3.2 receiver sensitivity estimates

CC2591 is receiving high-gain mode, HGM = 1, the external antenna with an internal T / R selector to the internal LNA noise figure NF is 4.8 dB, the internal back-end CC2531 signal to noise ratio can be resolved SNR is 3 dB (to ensure a certain level of error rate), single-channel transmitter receiver bandwidth BW can be set to 1 MHz or 5 MHz. According to the formula, when the normal temperature when T0 = 290 K, 1 Hz noise power bandwidth for the N0 =- 174 dBm, receiver sensitivity S =- 174 dBm + NF + SNR +10 log (BW). Parameters can be substituted

: receiver bandwidth 5 MHz, the receiver sensitivity S =- 99.2 dBm.

3.3 communication distance estimated

In the real environment, communication between any two points, environmental loss caused to the transmission waves are generally not quantitative estimate, and vary according to environmental changes. Without taking into account external influences and the transmission loss, electromagnetic wave propagation in the ideal case conditions, the wireless communication transmission distance is calculated as follows:

Loss = 32.44 +20 lgd +201 gFreq

Not consider the antenna gain (antenna parameters according to the actual purchase may be). Loss for the link loss budget of 118.2 dBm (loss excluding non-ideal), frequency Freq to CC2531 for RF center frequency of 2450 MHz, he may have wireless communication transmission distance d = 7.93 km. Practical applications to meet this distance, this value is for reference only.

4 Principles of wireless communication module

Mentioned in the overall block diagram of CC2531 is no longer the main external circuit here described, CC2531 and CC2591 connection to the circuit shown in Figure 2. Including inter-chip RF matching link differential signal lines, RF signals to the antenna matching circuit, CC2591 control signal lines, and power supply decoupling filtering section.


Figure 2 CC2531 and CC2591 connection diagram

Which supply line decoupling filtering section, B1 for the beads, options, should pay attention to their effective filter frequency range; the same time, other components have to choose for high frequency capacitors, inductors. RF signal to the antenna matching circuit, the antenna port with SMA connector (female), allows for the measurement circuit analyzer and vector network analyzer access more convenient, can also be connected with a corresponding antenna SMA connector . For the CC2591 the three enable control, distributed as follows: P0.1 HGM_EN, P1.1 PA_EN, P1.4 LNA_EN. Among them, the control of the P0.1 HGM_ EN GPIO can be replaced by any of the other two you can not change. They were mapped to the internal interface to the system stack and registers.

5 PCB circuit

Compared to the schematic design, PCB design and production in the actual circuit board will encounter more and more practical issues. Figure 2 shows the schematic design portion of the RF signal line wiring. Figure 3 shows the frequency difference between the chip alignment, Figure 4 shows the connection for the CC2591 RF antenna alignment. Figure 3 and Figure 4 shows the RF traces the main part of the layout design, the most common use of radio frequency island-style routing. Because of their frequency in the 2.4GHz, 20 dBm and the maximum power level, in the schematic do not see a lot of reflection, but in the PCB wiring may be caused by the irrational part of the larger local reflection, the accumulation of energy, led to the design and production failures. Therefore, all of the RF signal lines as far as possible into a linear design.


Figure 3-chip radio frequency difference between the traces


Figure 4 CC2591 RF antenna connector alignment

SMA connector antenna connector part of the selection. Figure 4, the connected components B8 and SMA connector portion 50 microstrip line, the actual production to the impedance control. Finally, the surface of copper in the design shop, to ensure good RF ground.

PCB design is completed the actual production process, due to parameters such as dielectric constant and dielectric height is not ideal according to expectation setting, inevitably there is bias, so should always pay attention to the parameters, time to adjust.

Set single-channel transmission, CC2531 internal TXPOWER = 0xD5 (typical transmit power +1 dBm), measured at 2.401 GHz center frequency, the power of +19.21 dBm. Although affected by other factors, this result is too large output power than scheduled, but acceptable. The results show that the radio link system, the ideal part of the transmission, reflection in the real circuit and loss of control of the project within an acceptable range. The corresponding receiver chain, but also predict the reflection and the loss is acceptable.

Conclusion

According to actual requirements, design and production to increase the transmission power to extend the transmission distance of wireless sensor network nodes. From the measured data showed that hair cells do add power amplifier greatly improved the node transmission power. Because of equipment and measurement conditions, the measurement of some other parameters did not carry out, this is where the future to improve, for the improvement of the circuit is one of the priorities for future work.

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