Are you "professional" in LNA selection and design in WLAN?

5V, 35pF, bidirectional ESD protection diode

WLAN is the abbreviation of WLAN . The full text of English is WirelessLocalAreaNetworks. As an alternative or extension to traditional wired networks, WLANs liberate individuals from the desk by using wireless technology to transmit data, voice, and video over the air, enabling them to access information anytime, anywhere. This article will introduce the selection and design of LNA in WLAN by taking Infineon's various cost-effective products as examples.

First, choose the right device

Take a dual-band WLAN product as an example. The main working principle block diagram is as follows:

Figure 1: Block diagram of a dual-band WLAN operating principle

In response to the above principle block diagram, the internationally renowned semiconductor manufacturer Infineon Technologies has introduced a number of cost-effective products, mainly LNA , Switch and ESD protection diodes, as shown in the following table.

Table 1: Infineon Technologies' Variety of Cost-Effective Products

In the above picture, the red part represents a new product, which has a higher cost performance than the old one. Among them, the low noise amplifier BFP840 has three models, the main characteristics of which are as follows, the research and development personnel can choose according to their actual needs.

Second, the design of the device performance evaluation

After selecting the appropriate part number, if the designer needs to simulate the performance of the device at the beginning of the design, Infineon official website provides simulation models of both ADS and MWO software. As shown below.

Figure 2: Simulation model of InfineonADS and MWO software

If you feel that the results of the simulation are for reference only, not objective enough, the designer needs to actually evaluate the performance of the device. We can provide the DEMO board as shown below and help solve any problems encountered in the actual test. In addition, the DEMO board is made of FR4, which completely simulates the design of real products.

Figure 3: InfineonDEMO board

After selecting the device to evaluate the performance, it begins to enter the design phase of the schematic. At 5 GHz, the recommended design circuit for the BFP840 is as follows:

Third, the schematic and layout design

Figure 4: BFP840 Recommended Design Circuit

The reference circuit requires a total of 12 RC sensors. To ensure good performance, please use RF-specific inductors and capacitors.

After entering the PCB design stage, the recommended PCB layout is as follows. In the process of setting the impedance line width and calculating the impedance, please try to ensure that the line width of the impedance line is close to the width of the device, mainly considering the continuity of the impedance.

Figure 5: PCB Design Considerations

In addition, since the frequency of 5.8GHz is relatively high, please pay attention to the grounding requirements of the grounding pin of BFP840, as shown below:

Figure 6: Grounding Requirements for BFP840 Grounding Pins

Through the above description, in the WLAN system, the initial design process of the complete LNA has been roughly completed, and the subsequent need to complete the system design, such as the reservation of the matching circuit (and switches, antennas, transceiver chips, etc.), the power supply Design and layout, RF grounding and digital grounding and other related issues.

When the system PCB is completed, it will enter the system test and debug state. For the performance of the LNA device itself, most of the features can be understood during the test of the demo board, but the system-related performance, such as receiving sensitivity. Features such as blocking are required to be completed at the system level. Because each system is different, we can't discuss it one by one. Here we only use LNA's design process to inspire others. We hope to have some inspiration and help for designers. More content welcomes designers and related technologies. Staff conduct more professional communication and discussion.