Bluetooth Low Energy chips get fast test
Testing Bluetooth Low Energy wireless devices can benefit from combined physical layer parametric measurement and functional communication test, writes Luke Schreier, senior group manager for automated test at National Instruments.
While much of the mobile and wireless communications market has been focused on increasing data bandwidth in standards such as 802.11ac and LTE-Advanced, another set of significant advances has occurred on the other side of the wireless communication landscape: low-power.
The mobile device has not only introduced us to the concept of streaming video and web browsing wirelessly, it has also introduced short range, low-bandwidth communication to ear-pieces, heart-rate monitors, speed sensors and contactless payment systems.
To accommodate this, communication standards such as near field communication (NFC), Bluetooth Low Energy, ANT/ANT+ and ZigBee (802.15.4) are becoming widely deployed.
From a development and testing perspective, these standards can require a different approach.
Bluetooth Low Energy, the latest version of the Bluetooth specification (4.0), is particularly interesting in applications like vital statistics monitoring, where information is transmitted in small chunks and long battery life is extremely desirable, especially in the case of implanted biosensors.
Compared with previous versions of Bluetooth that featured data transfer rates of 1-3Mbit/s, the low energy version accommodates around 200kbit/s transfers with very low duty cycles yielding average currents in the microamps.
It is the ability to handle these low duty cycles through a modified protocol stack that makes the low power consumption possible; transmitting continuously using Bluetooth Low Energy might actually use more power than previous versions of Bluetooth.
The process for testing wireless communication chipsets often involves placing the device in a “test mode”, where it functions in non-standard ways that make it easier to validate the RF parameters that will more than likely lead to successful communication.
This has often replaced the earlier forms of full communication functional test which were computationally heavy and slow, especially for cellular standards, and often too inefficient or complex to execute on a production line.
For a Bluetooth Low Energy chipset, the device could be made more efficient by eliminating the logic necessary to configure and execute these test modes, and time to market could be improved by eliminating the design, implementation and testing of this additional functionality.
However, you’d need to spend more time performing full functional testing on the production line. In this way, it has presented a difficult business trade-off in bringing silicon to market.
The PXIe-5644R vector signal transceiver from National Instruments includes capabilities that can help address both the physical layer parametric measurements as well as the functional communication test.
This is a vector signal analyser and generator combined inside the same module with an open, user-programmable FPGA for real-time signal processing and control.
By having a user-programmable FPGA on the instrument, we can embed the intricacies of the communication protocol, as written natively in LabVIEW or in a digital verification test bench, directly into the I/O stream of the generator and analyser.
This offers the ability to perform the functional communication test for Bluetooth Low Energy inside the vector signal transceiver.
Consequently, there is no need to wait for a vendor to implement the IP in a traditional instrument or deal with the slower-execution speeds of a transmit/receive stream across multiple instruments.
Also the vector signal transceiver can perform RF parametric measurements as the communication is happening. This combines functional as well as parametric test in real-time without adding additional logic to the device.
By making the vector signal transceiver protocol-aware through a user-programmable FPGA, the design and test complexity is greatly simplified and open to the user.