"From Human Interface Equipment (HID) to INT (IoT) Remote Sensors, facing the wireless connection in many applications, the designers have a lot of choices. One of the most basic, but also makes many designers feel tricky design decisions. Yes, it is a standard RF interface (such as Wi-Fi, Bluetooth or ZigBee, or the proprietary RF physical layer (PHY) design and protocol.
There are many reasons why some standards rather than another, but the relative weighing of cost, security, power consumption, interoperability, design time, anti-interference, coexistence, delay, and verification requirements. Many of them are related to each other, so the designers must first determine the design requirements and then perform corresponding optimization.
This article will discuss factors that need to be considered when the standard Bluetooth interface is selected between the standard Bluetooth interface and the proprietary RF protocol. Then, in turn, a Bluetooth 5 module and a silicon solution that can implement proprietary protocols thereon, and provide respective guidelines for how to quickly establish and run the solution.
Excellent range of radio frequency
If the design requirements are optimized for security, low power, small packages, and performance, they are suitable for adopting proprietary PHY and protocols.
From garage doorkelics to IOT equipment, security is critical to many applications. Use proprietary radio to solve this problem from multiple aspects. First, there is a designed design to ensure "hidden security", because not known RF interface is more difficult to break. In addition, there are more and more deserialized interfaces, or in a closed system that is not connected to a larger-scale network, thereby remained hidden states. Finally, designers with exclusive interfaces can freely develop their advanced encryption algorithms or to adjust existing algorithms without having to maintain interoperability with other manufacturers' security algorithms. Different, this is a security advantage.
Faced with interference from Wi-Fi networks, microwave, cordless phones, and other low-power wireless networks, using proprietary radio design facilitates ensuring a robust connection. Due to no binding criteria, designers can flexibly use techniques such as direct sequence spreading (DSSS) and frequency hopping spreading (FHSS) to better use the frequency band. In addition, they can adopt their preferred coding schemes based on the expected link budget to achieve higher throughput or lower power consumption.
This flexibility is equally applicable to the data packet structure. The data package structure does not require packet overhead to ensure interoperability between standard wireless devices, so it can be streamlined according to application requirements.
From a hardware design perspective, due to the designer of the proprietary RF interface clearly understands performance requirements and determines that these requirements do not change in subsequent phases, it is possible to optimize the design of space, power consumption and performance. On the other hand, they can also achieve the above optimization by including only the necessary functions that meet the application needs.
Although there are many advantages, other factors must also be considered. The first is cost: It is necessary to demonstrate the rationality of the non-regular engineering (NRE) cost brought by custom radio frequency IC design and related software, especially for low-cost equipment, the expected yield should be more than 100,000.
The closely associated with the cost is the design time, especially considering the change of RF design, well-known radio expertise, and the time required to develop firmware and software required for successful design.
Bluetooth is widely used and has been adjusting
Bluetooth is just at another extreme. Bluetooth initially designed as a simple point-to-point cable replacement technology for HID and other devices involving users, but it quickly develops a wireless audio and device to device connection solutions. Thanks to the strict control of the Bluetooth Technology Alliance (SIG), Bluetooth has become well known standards, regardless of hardware sources, designers can confirm that their equipment can connect to other support for Bluetooth and interoperability.
Bluetooth has widely used numerous interoperable equipment that achieved rich hardware and software, making the design of wireless interfaces to be available at a lower cost. In addition, Bluetooth has been developing for many years.
It has been working in a 2.4 GHz industry, scientific and medical (ISM) band, initially for GFSK modulation for its 79 1 MHz carriers, thereby providing 1 Mb / s throughput. This throughput is called the Bluetooth Basic Rate (BR). Bluetooth can continue to maintain a steady state while facing interference, even in the process of constantly introducing more wireless connecting devices, even in the IOT. In order to achieve higher data rate, Bluetooth 2.0+ enhanced data rate (EDR) uses π / 4-DQPSK (differential orthogonal phase shift keying) and 8DPSK modulation, 2 Mb / s and 3 Mb / s respectively rate.
Although Bluetooth is strictly controlled by SIG, designers still need to study the changes brought about by the Central Regulation of Bluetooth 4.0 launched in 2010. This specification references low-power Bluetooth (BLE), its previous market name is intelligent Bluetooth. BLE cannot be compatible with classic Bluetooth backwards, and designers need to pay special attention to this.
The main goal of BLE is low power consumption. The method of achieving this is that the connection guide method from classic Bluetooth (at this time, the device always maintains the connection state) is transformed into an unconnected method (at this time the device is only connected to a shorter interval time). Such applications include wearable devices such as smart watches and IOT sensors.
The Bluetooth SIG continues to improve specifications to meet the needs of its members and applications.
The latest version of Bluetooth 5 uses a stronger forward error correction (FEC) algorithm, can double the BLE data rate, that is, increased from 1 Mb / s to 2 Mb / s, and connect 128 kb / s connection range Expand 4 times to last 50 meters. The higher the data rate, the more data packets transmitted within a given time slot, and the device power consumption can be reduced due to the low power consumption or standby mode due to the device.
A further distance allows designers to make more flexible trade-offs between data rates and distances for any Bluetooth device including beacons. The beacon is a battery-driven BLE device that broadcasts its identifier to the nearby mobile device so that these devices can perform specific operations when approaching the tribute. The beacon is widely adopted by advertisers, and it can also achieve accurate indoor and outdoor tracking.
However, SIG also implemented another exclusive RF interface designer can also try interest adjustments: they reduce the overhead and payload ratio, thereby reducing the number of transmitted times required to send a given number of "real" data, further Reduce power consumption.
Bluetooth initially acts as a simple cable replacement technology, and now has evolved into a practical technology. Therefore, designers are now more inclined to adopt fast, simple Bluetooth solutions, rather than investing a lot of cost and cost design of their RF interface.
Establish and run Bluetooth solutions
As the design's listing time window continues to narrow, the design budget is constantly tightening, and the trend of using Bluetooth interfaces will gradually become necessary. Fortunately, for many designs, there is still enough space to accommodate the ready-made Bluetooth modules, allowing the design team to focus on their final application and achieve competitive advantage.
Rigado's BMD-330 Bluetooth 5 module belongs to such modules (Figure 1). Although there are many Bluetooth modules on the market, this module is particularly interesting and practical due to the onboard integrated antenna. Antenna matching and mounting is one of the fine work in RF design, such as the task can be shared for designers, and saves time and ensures optimal signal coupling.
This module is a complete solution that meets regulatory licenses, with its own onboard DC-DC converter and smart power control, with a size of 9.8 x 14.0 x 1.9 mm. Although an antenna comes, it still requires a suitable ground plane to effectively radiate signals. In addition, there is no copper and other metals from the area extending from the antenna portion of the module, and the module should be placed on the edge of the PC plate and the antenna outward.
When you install the module inside the housing, make sure there is no metal near the antenna, otherwise the performance may be affected. Since the design and adjustment of the module is targeted in a non-enclosed space, it is possible to affect performance, and additional measures need to be taken after the application. The budget is in line with the requirements of the specification.
This module is built based on Nordic Semiconductor's NRF52810 system (SOC) (Figure 2). The SOC uses ARM® Cortex®-M4 CPU with a clock frequency of 64 MHz and has 192 KB flash and 24 kb Ram.
The flash space of the module is not large, so Rigado does not provide any factory firmware in the module. Since there is no boot program, any firmware needs to be loaded using a serial line debug (SWD) interface. However, after this operation, Nordic provides a number of protocol stacks called soft devices. These protocol stacks are binaries pre-compiled and pre-link, which can be downloaded from the Nordic website. The BMD-330 supported by NRF52810 SOC supports S132 (BLE Central and Peripheral) soft equipment and SME-optimized S112 (BLE peripheral) soft equipment.
The main specifications of the BMD-330 module include the transmit power of +4 DBM and the receiver sensitivity of the -96 DBM (Ble mode). It uses a 3 volt supply source that consumes 7.0 mA (mA) current when the power is +4 DBM, and the power is consumed by 0.6 mA when the power is 0 dBm. In reception mode, the rate is 4.6 mA when the rate is 1 Mb / s, and the speed is 5.8 mA when the speed is 2 Mb / s. The transmitting and reception specifications assume that the DC-DC converter is enabled: the current will increase after disabling.
Present RF and Bluetooth Binding
There is another option between complete custom proprietary radio design and standard Bluetooth: Designers can develop their own protocols and coding schemes based on ready-made radio transceivers, or with ready-to-build ANT, Thread or ZigBee. As the cost of the available silicon solutions continue to decline, plus a wide range of software support, if you want to get competitive advantages, you must optimize space and enhance security options, which provides the best binding band while keeping Extremely low costs do not need to change the design schedule.
Silicon Labs EFR32FG14 Flex Gecho Proprietary Protocol Series SOC (Figure 3) provides a nice option for interested designers with this design path.
Like BMD-330, EFR32FG14 also uses the ARM® Cortex®-M4 core, but the maximum frequency is 40 MHz instead of 64 MHz because the chip is specifically for low power IOT applications. It has up to 256 kB flash and 32 kb Ram. Note that the chip supports 2.4 GHz and SUB-GHz (915 MHz) operations and provides an antenna network matching guide. It also supports an antenna diversity and can alleviate the influence of frequency selective decay.
There are also a variety of flexible I / O and security functions, including: 12-channel peripheral reflecting systems that can be independently interactive for MCU; up to 32 GPIOs; and hardware autonomous encryption accelerator and true random number generator . The chip also integrates a power amplifier for 2.4 GHz and Sub-GHz operations.
To assist in the completion of the development process, Silicon Labs also provides SLWRB4250A boards for EFR32FG series (Figure 4). It includes SOC, pin, crystal, and antenna matching circuit, and software.
Summarize
There are many reasons for choosing a complete proprietary RF design path or standard Bluetooth radio. Each choice has its own advantages in meeting cost, time, performance, size, security, etc., and many other factors. However, if the designer wants to get a variety of costs and time from the existing silicon solution, it is also necessary to flexibly add some existing competitive advantage, and suppliers now provide a reliable hardware platform for its construction. Such a solution.
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