Far Field Communication System 

Components

Application processor

Wifi and BT Combo Chip Module

• • Integrated transceivers (i.e mixer, PA, LNA, etc.)

  • Integrated network/baseband processors

  • Integrated MAC controller

  • Peripheral,PMU, Clock, memory, etc.

Dual band Antenna

• • Dual band antenna supports two distinct frequency ranges. In this case, it's the frequency range for wifi 802.11 a/b/g/n/ac and bluetooth.

T/R Switch

• • It provides directional isolation for receiver when transmitter is on in order to avoid damage to receiver due to high transmitter power.

Diplexer

• • it provides frequency isolation between two bands (i.e as 2.4 GHz and 5 GHz bands) and allows independent operation between two 2.5GHz and 5GHz transceivers  while sharing one dual band antenna. Operating efficiency and cost and space reduction are achieved.

BPF (band Pass Filter)

• • band pass filter is used to prevent out of band noise.

Host interface

• Bluetooth: 

  • UART for control 

  • PCM for audio

• Wifi: 

  • SDIOV3.0 for control and data

Design Analysis

Placement

The antenna should be placed is opposite directions two maximize polar pattern coverage.

Layout

• Does not use  power plane for RF ICs. Power plane does not provide enough isolation for RF power pins, which is needed to reduce noise leakage among RF components.

• Use star connection for power for RF components.

• RF component and paths requires ground clearance in the layers below to avoid signal attenuation. Follow RF routing guideline of from the vendor

• Use via fensing for all RF traces ideally the spacing between each successful via is < 1/10 of the smaller RF wave length of signal of interest. This provides noise immunity to RF signal and most important creates a PCB wave guide for RF signals.

Design trade offs

Why choosing a wifi/bt combo chip module?

As a system designer with limited domain expertise in RF system, selecting WiFi and Bluetooth combo chip module simplifies design, RF testing, and cerfitication. There is a lot of module vendors who sells wifi/bt compliant module in a easy assembled system in package parts.

Are there an alternative to buying a module?

One can use the chip by itself and design in the necessary matching network, RF switches, and amplifiers to save cost and space. This is design approach generally referred to COB, chip on board; however one needs to be very stringent is RF components selection, layout, and testing. 

Why using a dual band antenna?

Dual band antenna as the name suggests that this antenna supports frequency range on two bands, 2.4 GHz and 5.0 GHz respective; therefore, there is no need to use two separate antenna, one for each band, resulting in cost and space saving.

Why using SDIO 3.0 interface for wifi Host interface?

Wifi host interface is not limited to SDIO. Other common supported interface would be PCIE and USB. However SDIO is extensively used to interface with wifi and bluetooh chips.

How does Wifi and BT radio coexist on 2.4 GHz band without collision?

Traffic Collision avoidance is achieved via a signaling handshake system between wifi and bt radio to coordinate for transmit and receive. For instance, bt radio send a request to wifi radio for transmission, wifi radio grants that request and delays its transmission.

Where is the antenna for bluetooth radio?

Both wifi and bluetooth operates on the same frequency range on 2.4 GHz ISM band; therefore, it shares the same antenna with WiFi radio. Another cost and spacing saving in this design.

What are some popular wireless vendors?

Broadcom and Realtek are quiet common for cost friendly parts.

Compliance

All wireless devices must undergone compliance test in regulator agencies such as FCC and CE. Example RF testing standards for CE are EN 300 893 for 5G and EN 300 328 for 2.4G.

Summary & Conclusion

We learned that far field radio transmission allows longer range communication compared to NFC. Wi-Fi and Bluetooth are the most popular standards. We see that most of wireless system can be done quiet easily by buying a certified module. All the designer needs to do is select the right antenna, following strict RF placement and routing guidelines, and lastly select the correct host interface to communication with the application processor. 

As we can see, RF design is challenging but manageable if we pick the right parts.

Further reading

To learn more about Wi-Fi coexistence please see following links: silicon lab learning center and Texas Instrument Application Note.

To over the overall about Wi-Fi Physial Layer and testing, please download the poster from following link: TEktronic WIFI Poster

To learn about Bluetooth Physical Layer and testing, please download the poster from following link: TEktronic BT Poster