Wireless Products: SoC VS. SDR, Part 1
The requirements of a wireless product design should drive the technology and solution. Numerous technology solutions have been optimized in an all on one System-on-chip (SoC), while a Software Defined Radio (SDR) allows a great deal of flexibility. So which one is preferable when designing your product? On today's blog, we'll cover the SoC solution.
GPS receivers, Wi-Fi, Bluetooth®, and Zigbee are common solutions in a vast variety of wireless products. GPS is found in everything from cars, airplanes, boats, trains, phones and has many other uses. Wi-Fi enables wireless networks, Bluetooth enables wireless headsets for cell phones and Zigbee is in numerous smart energy and home automation products.
Bluetooth, Zigbee, Wi-Fi and even cellular solutions have been reduced to one SoC transceiver design. But, they come with a rigid set of specifications that my not solve or meet the design or cost requirements. Although SDR allows flexibility, they generally come at a higher cost. Some designs start as a multi-chip and evolve over time into single or higher integrated designs.
Licensed VS. License-free Spectrum
Communications can take place over privately licensed spectrum or license-free spectrum. Cell companies have spent billions on new licensed spectrum for deploying their 4G networks. Paging networks, satellite television, AM, FM and television broadcasting are all users of licensed spectrum. Many of the license spectrum users are able to have a transmitter that broadcasts with an output power of several watts to thousands of watts, enabling long range communications.
Government, military, marine, railroad, and aircraft also utilize licensed communication in everything from voice and data communications to radar.
With licensed spectrum, companies purchase spectrum licenses from the FCC, giving them exclusive access to certain frequencies within a geographic area. The FCC allows licensed radio systems to use high-power transmissions (usually greater than 1 watt) on their assigned frequencies. Licensed spectrum is a scarce resource that is difficult and expensive to acquire in large blocks. Because of these constraints, these vendors often possess just several hundred kHz of spectrum, providing only a handful of channels. The licensed spectrum is normally only useful for narrow band communications. Cellular 4G and WiMax spectrum is an exception.
FCC spectrum licenses are not permanent. In addition, the FCC can reallocate spectrum for other uses and has done so in the past.
Unlicensed spectrum for commercial use is available for no cost. Unlicensed spectrum includes the CB, FRS, and the industrial, scientific and medical (ISM) band, at 13.5, 27, 40, 433, 915 MHz, and 2.4, 5.8, 24.1, 61.2, 122.5, and 245 GHz bands. To minimize interference, the FCC restricts the maximum transmit power for unlicensed devices and requires the use of spread spectrum technologies. SoC transceiver solutions are available for most of these frequency bands with the exception of CB and FRS bands. The CB and FRS bands are special cases and limited to only this type of transceiver modulation.
SoC Radio Solutions
SoC solutions come in many different forms. Many are standards based: Wi-Fi, Bluetooth, Zigbee, RFID, NFC, and GPS. Proprietary solutions also exist when a standards based solution doesn’t meet the requirements. Samplings of SoC transceivers that are available are shown below:
The SoC transceivers are very highly integrated and very cost effective. Most require very little support circuits other than a microprocessor for controlling, power supply and an antenna. Below is a simplified Block Diagram.
The receivers usually are direct conversion architecture. This architecture is the ideal choice for highly integrated receivers, reducing the bill of materials by fully integrating all inter-stage filtering. The front end includes low noise amplifiers (LNAs) feeding mixer for down-converting to a low or zero-frequency intermediate frequency. Integrated receiver filters usually offers selectable bandwidth and data rates. Analog to digital converters complete the RF signal to digital data translation.
Majority of the transmitters offer direct conversion modulators. They may integrate a transmit amplifier and filter.
Integrated phase lock loops (PLLs) provide high performance frequency synthesis for both receive and transmit sections. Some VCO and loop filter components are fully integrated.
Adding an antenna as the air interface, a MPU for control and data decision with a power source such as a battery make a very highly integrated, low cost system.
Many SoC designs can be improved with the addition of external transmit power amplifiers (PA) and receive low noise amplifiers (LNA). They increase the transmitter output power and receiver sensitivity respectively (See Figure 3). Many times these are realized with a module or IC, which integrates these functions.
The range extension increases output power and sensitivity as show below.
Part 2 will discuss the advantages of SDR with a final conclusion on which is preferable in your product design.