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Signal generator leverages fast pattern-memory architecture

Posted: 18 Apr 2005 ?? ?Print Version ?Bookmark and Share

Keywords:ate instrumentation? test equipment? anritsu? mg3700a? generator?

Whether your need is for lab or ATE instrumentation, test equipment selection these days can spell tough sledding, especially in light of tight new equipment budgets. Given these constraints, Anritsu's new MG3700A generator looks like it could fill the bill with respect to price vs. performance.

That seems especially true due to its built-in ARB (arbitrary waveform generator) and BER (bit error rate) measurement capabilities. If your intent is to run this box in ATE, you'll benefit from fast switching and an electronic step attenuator, too.

Look to the future

This instrument also shapes up as a platform to support future requirementsand at reasonable cost. It appears adaptable to meet the needs of emerging next-generation systems, such as the NTT DoCoMo communications system under development right now in Japan. This mobile network is anticipated to run data uplinks cranking away at more than 20Mbps, with downlinks running at 100Mbps.

Whether your needs are immediate or future oriented, you can use Anritsu's new MG3700A to evaluate and test baseband chips, sub-components, and all sorts of broadband RF gear, including complete chassis-level systems. For receiver testing, for example, the MG3700A can serve as both a signal source and an interference signal source. It can also serve as a reference signal source when testing filters, mixers, power amplifier blocks, and modulators and demodulator circuits.

Wide range
As Anritsu's press statement (on the left) notes, its new generator can cover a frequency range from 250kHz all the way up to 6GHz. The (optional) 6GHz upper frequency range is just what's needed for WLAN (wireless local area networking) tests in the 5GHz band. That upper range should come in handy as well when testing next-generation communications systems that are pushing into the higher frequency allocations, too.

Not stated is that you can set the MG3700A's frequency to within 0.01Hz. Pretty good resolution, eh? And, if you need a system with exceptional frequency stability, you can also order a rubidium reference as an option.

The press statement refers to high accuracy a number of times. Accuracy, low phase-noise, and low non-linearity is desirable in any piece of RF test equipment, but in microwave testing it ensures that much-needed level of confidence that sometimes seems elusive at those frequencies.

Look at the instrument's absolute level-accuracy. It's typically within 0.5dB up to 3GHz, degrading to only 0.8dB above 3GHz. Linearity is typically within 0.2dB.

Output levels can be set anywhere from -140dBm to 13dBm for CW, and from -136dBm to 6dBm using vector modulation. A mechanical attenuator option lets you set output from -140dBm to 19dBm.

The company's release also mentions wide vector-modulation bandwidth. It's 120MHz using the box's internal baseband signal generator, and can be as high as 150MHz if you feed an external I/Q (in-phase and quadrature) input. The 150MHz vector modulation bandwidth works all the way up to 6GHz. That's just the ticket if you're developing systems that use wide bandwidths and multiple carriers.

High-speed Ethernet
As communications systems move into that lofty wideband regime, and data rates on those RF links get ever-faster, long waveform patterns must be transmitted. To accommodate long patterns at speed, the MG3700A supports 100BASE-TX Ethernet connectivity for transferring waveform files to the box from your PC.

Waveform patterns of two or more MG3700As can be updated as well. In those cases, waveform data can be simultaneously transmitted to multiple boxes across your LAN, with transmission of patterns taking place at speeds to 2MBps. Waveform files (more on these in a moment), as well as firmware upgrades, can also be transmitted that way.

From disk to RAM
In use, I/Q sample data is loaded to baseband memory, and the desired signal is repeatedly generated. Since simulation signals can be generated arbitrarily, flexibility is high. Typically, signal generating capability was limited by baseband memory length or sample rate. That's where the MG3700A's memory architecture shines.

Any patterns, as well as related parameters, once transmitted to an MG3700A, can be saved to the target generator's hard disk. Notably, the transmission speed between the hard disk and internal waveform memory in these units is quite high; 14MBps is typical. Also, because the patterns are read from the system's hard disk and then saved in RAM, they're outputted rapidly without having to re-access the system's hard drive.

Speaking of memory, the MG3700A's ARB waveform array supports lots of storage. A Gigabyte of memory is standard and it can store 256Msamples/channel. If you need more, you can optionally increase memory to 2GB, and store 512Msamples/channel. With that large capacity many waveforms can be saved simultaneously.

Four types of waveform patterns can be implemented on an MG3700A. You can use standard waveform patterns, or waveform patterns generated by a waveform pattern option. You can also use waveform patterns generated by Anritsu's waveform generation software (more on this below), or your own custom-rolled patterns crafted in popular PC-hosted math software packages.

In use, the MG3700A's dual arbitrary waveform memories can each choose one waveform pattern. Then, the generator can output the signal of either one of the memories, and can also combine and output both signals simultaneously.

Combining signals is neat. For example, if you're measuring receiver characteristics, such as adjacent channel selectivity or blocking, the desired signal-plus-interfere and the desired signal plus AWGN (additive white Gaussian noise) can be outputted by just one MG3700A.

Since digital processing is used for adjustment and S/N (signal-to-noise), the system maintains accurate level-ratio accuracy, too. Using one signal generator for such tasks can save you a lot of money that might otherwise be spent on multiple instruments.

PC-produced waveforms
Anritsu's press release makes brief mention of the optional IQproducer software for crafting custom signal patterns. But, the company doesn't mention that its bits are PC compatible. Your computer will need to run a Pentium-III clocking at 1GHz or better to run it, and be equipped with at least 512MB of RAM. IQproducer runs under Windows 2000 Professional, or Windows XP.

Once installed, IQproducer takes a text file of I/Q data generated by software such as MATLAB, and converts it to a waveform file. Its graphical interface lets you set parameters, and you can also save them to files for recall. Before transmitting a waveform pattern to the MG3700A itself, the pattern can also be checked graphically using IQproducer.

Lastly, Anritsu also supplies freebie application drivers for IVI and National Instruments' popular LabVIEW programming environment.

- Alex Mendelsohn

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