The mobile industry’s chipset interconnects are going through a standardization process similar to that experienced by the PC industry several decades ago. Bus standards help accelerate the handset design process by reducing hardware integration effort, eliminating glue logic between devices, and facilitating the migration to new generations of ICs.
As an example, the MIPI Alliance DigRF v4 specification defines the digital interface between a BBIC (Baseband IC) and an RFIC (Radio Frequency IC) in a single terminal. This interface replaces the traditional analog IQ link and supports high-bandwidth transfers for mobile systems incorporating high throughput standards such as LTE. The same DigRF bus enables both control and digitized IQ data transfers for multiple channels, reducing the number of pins on the IC. The specification has been updated to follow the evolution of wireless standards including the addition of MIMO and carrier aggregation.
With the migration from analog IQ signals to high-speed serialized packet transfers, the architecture of an RFIC characterization test bench is evolving from a combination of analog RF sources and vector signal analyzers towards an arrangement of cross-domain tools able to send and measure packetized IQ information on the baseband side, all while performing RF stimulus and analysis on multiple channels on the RF side. I’ll now review the automated test challenges that arise as transceiver manufacturers need to test more (frequency ranges, standards, bandwidth, etc.), within the same amount of time, and provide an overview of high speed solutions for DigRF-based transceiver test.
Test Challenges
Like most high speed serial busses in computers, the DigRF interface specification is described as a protocol stack, including physical, transport and application layers. It defines the physical signals, bus operation, packet structure, data encoding scheme, flow control and error-handling mechanism, and more.
Because DigRF is designed to transport IQ information, there is another protocol stack encapsulated within the digital interface. The wireless protocol stack represents the wireless protocol operation of the mobile handset. As with other protocols, this stack definition (Figure 1) starts at the wireless physical layer and goes to the wireless application layer.
From RFIC design to mobile system integration and production, the design team needs to validate the proper operation of each layer of this “dual” protocol stack. During validation, characterization and production, most of the testing is focused on the RF performance of the transceiver, which requires a combination of DigRF test instrument, combined with RF sources and analyzers. Here are several examples of emerging test challenges related to DigRF.
source: http://www.edn.com/design/test-and-measurement/4431350/DigRF-devices-need-RF-and-protocol-tests-
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