Moore’s Law meets RF

USA: The benefits of Moore’s law have increased performance and reduced cost for electronic products for more than half a century. The development pace and proliferation of mobile devices have leveraged Moore’s law, growing at a projected 24.9 percent CAGR for 2011–2017 (ovum.com, May 3, 2012). This trend is fueling significant silicon process developments for consumer electronics as well as pushing signal processing for features necessary to meet demand.

The digital revolution is not driving analog signal processing to extinction. In fact, just the opposite is occurring as the digital world continues its exponential expansion, the analog and mixed signal functions are growing in number, performance and diversity. As always, the challenge of providing “more” (functionality, bandwidth, dynamic range) for “less” (power, size, cost) will drive the technology forward, said David Robertson, VP, Analog Technology, Analog Devices Inc.

From a test and measurement perspective, traditional box instruments have not kept pace with this growth in an affordable, efficient manner. Because of stringent performance requirements, instrumentation has relied on more discrete design methodologies. Despite delivering accuracy and stability through these methods, box instruments are expensive, complicated to design, and often fall behind the pace  of change inherent in the devices they aim to test by failing to leverage benefits of integration.

RF instrumentation users will benefit from three trends that shift RF instrumentation on a trajectory to match Moore’s law: advanced CMOS technology, greater FPGA utilization, and optimized design with modular form factors.

Advances in CMOS technology
In traditional RF test equipment design, signal manipulation has been implemented predominantly in the analog domain. This means that large and complex analog systems need to be developed to amplify, filter, mix, and manipulate electric signals while dealing with physical realities of nonlinearity, noise, coupling, interference, power dissipation, and so on. This work requires significant investment and skill on the part of the developer, which leads to expensive instrumentation.

An alternative approach is to convert signals to the digital domain with a reduced amount of analog signal processing, resulting in a less expensive and more flexible design. This requires better data converters with improved bandwidth capability, increased linearity, and reduced noise.

Analog Devices states in its 2011 Trends in Data Conversion, “The wireless communications market will remain another key driver of data converter performance, power efficiency, and calculated integration…and it’s clear that the future of high-speed converters in this market will be defined by lower power consumption combined with faster sampling rates and more usable bandwidth at higher intermediate frequencies.”

Recent RF instrumentation incorporates the latest communications infrastructure data converters and zero IF modulators and demodulators. These architectures feature several advantages over traditional architectures including lower cost, less power consumption, and high selectivity. This capability is useful in testing the latest wireless and cellular connectivity standards such as 802.11ac and LTE.

Greater use of FPGAs in instrumentation
FPGAs are used for data manipulation and data processing as well as digital signal processing (DSP). DSP is different in the sense that analog signals are converted from analog into the digital domain by data converters, and then further manipulated in the digital domain. Having powerful and programmable FPGA-based digital signal processors at the center of test equipment has several advantages.

First, FPGAs are parallel in nature and can therefore perform complex mathematical calculations simultaneously without involving a host processor. The digital signal processor can convert large records of data into manageable blocks of information that can then be further manipulated or stored on the network. Another advantage of DSP performed on FPGA-based test equipment is that it is reprogrammable, meaning one piece of hardware can be used for various test applications, be it current or future standards-based testing.

A software-defined instrument also offers the ability to develop a custom application or update the device to the latest test applications. It thus becomes software-defined test benefitting from the rapid advances of FPGA development that is outstripping that of processors.

EEJournal states that FPGAs have walloped digital signal processors, conventional processors, and even graphics processors— both in terms of raw processing throughput on a single device and particularly when considering the amount of power  consumed (“Supercomputing Today, Tomorrow, Whenever,” November 15, 2011, eejournal.com).

The power of FPGAs has led to reduced cost and size of RF test equipment with RF performance to match the needs of high-volume RF test. An additional benefit of using FPGAs is massive reduction in test time. By synchronizing the timing of digital control with the onboard FPGA on NI’s vector signal transceiver with the RF front end of the instrument, Qualcomm Atheros decreased test times by more than 20X over previous PXI solutions and up to 200X over the original solution that used traditional instruments.

PXI - modular form factor
Building automated test systems to verify performance and quality of the latest electronic devices requires a combination of instrumentation, data buses, processing and data storage in a compact and reliable form factor. National Instruments introduced PXI in 1997 to meet  these requirements and evolve with Moore’s law.

For example, the first PXI systems sold in 1998 offered a Pentium MMX 233 MHz processor with up to 128 MB RAM; today’s PXI systems feature a quad-core Intel Core i7-3610QE 2.3 GHz processor with up to 16 GB RAM. This represents a more than 134X improvement in GFLOPS processing performance in the same form factor.

Significant CMOS and FPGA process developments, as well as the advances in modular form factors, have a disruptive effect on the cost, footprint, and test throughput of next generation RF test solutions.
The aforementioned growth in the mobile market implies a rapid adoption of new wireless standards, such as IEEE 802.11 ac and LTE.

To meet the ever-growing and changing testing demands, test equipment vendors have been designing RF test solutions in the preferred form factor of PXI. Recent PXI product announcements include vector network analyzers, vector signal analyzers, and vector signal generators from vendors such as Aeroflex, Agilent, and National Instruments.

Because the PXI form factor is constrained in power (~30 W per slot) and size (Eurocard formats), it is forced to adopt the latest technologies in data converters and FPGAs to remain competitive. Thus, it represents a viable commercial vehicle to ensure delivery of these benefits to RF engineers.

Moore's Law beyond 2013
Intel expects computing performance advancements in accordance with Moore’s law to continue beyond the next 10 years. Not only is this trend fueling significant CMOS and FPGA process developments for consumer electronics, it is fueling advances in next generation RF test equipment.

We are likely to see additional uses for technology propelled by fast-growing consumer electronic devices, which can have a disruptive effect on the cost, footprint, and test throughput of next-generation RF test solutions.

-- National Instruments, USA.