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Industry News

Mid-range Vector Signal Generator with Internal Signal Generation

October 15, 2008
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The world of telecommunications has experienced an accelerated period of change in recent years. In the past, many terminals such as mobile telephones and PDAs were only capable of transmitting and receiving signals based on a few different standards such as GSM and WCDMA. However, increasing numbers of functions and standards are now being integrated into terminal equipment (e.g. GSM, WCDMA, WLAN, WiMAX, GPS, FM radio and mobile TV).


In addition, the data rate to be transmitted has increased from a few kbit/s in GSM to target data rates of 100 Mbit/s in LTE, while the transmission bandwidth has grown from several hundred kHz to as much as 40 MHz in 802.11n. Modulation methods such as OFDM/OFDMA and other techniques such as MIMO have found a place in all of the new communications standards.

All of these advances are presenting new test and measurement challenges. For instance, developing and manufacturing equipment requires signal generators with all-round qualities and the capability of keeping up with the rapid development of modern technology. However, such generators must also be scalable so that users only have to invest what is necessary to meet their current test requirements.

It is a tough task for a mid-range vector signal generator to satisfy all of these different criteria, but the new, compact R&S SMBV100A vector signal generator is up to the challenge. Its RF characteristics are paired with a flexible baseband architecture and many useful add-on functions.

Figure 1 Measured maximum output power vs. frequency.

It is available for frequency ranges from 9 kHz to 3.2 GHz or from 9 kHz to 6 GHz. The vector signal generator is characterized by high output power of typically +24 dBm across its entire frequency range (see Figure 1). This is particularly advantageous with complex test set ups. Components such as cables, switches and couplers often cause significant power loss that requires adequate compensation. With the R&S SMBV100A, the use of external amplifiers can be avoided. This minimizes the overall uncertainty of the test set up and helps to avoid additional costs.

Figure 2 Measured SSB phase noise with internal OCXO (R&S SMBV-B1 option).

The new instrument also offers very good signal purity. The SSB phase noise has a nominal value of 128 dBc/Hz (20 kHz offset) at f = 1 GHz (see Figure 2). Non-harmonics undergo nominal suppression of better than 85 dB and the wideband noise has a nominal value of 152 dBc. The error vector magnitude (EVM) for signals such as WiMAX IEEE 802.16e and LTE is typically 0.4 percent, while the level repeatability has a nominal value of 0.05 dB.

Modulation Bandwidth up to 528 MHz

Today’s communications standards require more and more transmission bandwidth to handle the growing complexity of multimedia applications and the R&S SMBV100A is well equipped to meet the challenge. With internal signal generation, RF bandwidths of 60 or 120 MHz can be selected. Even multicarrier signals for wideband wireless communications standards such as WLAN IEEE 802.11n and LTE can be generated.

Figure 3 Frequency response of the IQ modulator with a bandwidth of > 500MHz.

With external I/Q modulation, the maximum RF modulation bandwidth of the R&S SMBV100A is 528 MHz. This allows up-conversion of UWB signals, which can be generated using the R&S AFQ100B baseband generator (see Figure 3, for example). At the same time, the large I/Q bandwidth ensures high time resolution for the signals.

Very fast baseband frequency hopping as used in military applications and generation of steep-edged radar pulses with complex modulation are thus feasible in conjunction with an external I/Q source such as the R&S AFQ100B. Thus, the R&S SMBV100A can replace more expensive vector signal generators, which are utilized solely for their large bandwidth and not any other capabilities.

Customized Internal Signal Generation

Customizing test instruments to fit the application is more or less a standard practice nowadays. However, the R&S SMBV100A implements this feature in an unusual way, being unique in its class by being equipped with a real time baseband coder for direct signal generation.

Alternatively, it allows selection between different versions of an arbitrary waveform memory from which pre-calculated waveforms can be played back. This means that a single platform can provide a solution that can be optimally adapted to requirements in production and development.

Table 1 Application-Specific Baseband Configuration

In production applications, standardized test sequences are required along with fast frequency and level setting times that the R&S SMBV100A also ensures with a value of <1 ms in the List mode. For playing back these test signals (which are generally pre-calculated), a total of four different versions of the arbitrary waveform memory (ARB) are available. Depending on the configuration, the instrument offers a bandwidth of 60 MHz or 120 MHz and an I/Q memory size of 32 Msamples or 256 Msamples (see Table 1).

This makes it possible to easily play back even long test sequences, which is a requirement for digital radio standards, for example. Additionally, the large I/Q memory enables the storage of different signals as part of a multi-segment waveform and switching between the individual signals in just a few microseconds. This is especially useful during production tests on multi-standard modules that are designed to support a wide variety of digital standards, e.g. GSM and UMTS. The test signals can be pre-calculated using either the R&S WinIQSIM2 signal generation software or third-party programs.

Table 2 Selection of Internally Supported Signals (with Additional Options)

In research and development environments, the R&S SMBV100A is useful due to its optional real time baseband coder. Test signals for all major digital communications standards can be configured directly on the instrument (see Table 2). Users can also avoid the hassle of having to pre-calculate the signals on an external PC and transfer them to the signal generator. This makes it possible to modify individual parameters quickly and easily while directly examining the effects on the device under test. Everyday work in the lab is accelerated, helping to shorten development time and design cycles.

The real time coder also enables generation of infinitely long test sequences, e.g. for simple digitally modulated signals as well as for internally generated digital standards such as GSM/EDGE and 3GPP FDD (downlink). Such long test sequences serve as a reliable basis for performing bit error rate tests, particularly in cases where long bit sequences are needed to ensure statistically meaningful results.

A True All-rounder

A signal generator is only as good as its interfaces. This applies to the interfaces for connecting to the device under test, for synchronizing with different test instruments and for handling remote control, as well as to the user interface itself.

In addition to the RF interface, the R&S SMBV100A also includes analog differential I/Q outputs as a standard feature, while an optional digital I/Q output will be available in the first quarter of 2009 (enabled via software). This makes the vector signal generator suitable for tests at the RF and in the baseband.

For the baseband generator, a wide range of trigger and marker functions are available to ensure accurate synchronization with the device under test. In the RF range, multiple signal generators can be interconnected using the phase coherence option. Usage of a common local oscillator (LO) signal ensures the phase coherence needed to make, for example, measurements on phased-array antenna systems (beamforming) or components with differential RF (e.g. amplifiers).

In the area of remote control, the instrument meets all needs; USB, LAN and GPIB interfaces are available along with the appropriate software drivers. An integrated VNC server also enables convenient remote control of the instrument via a web browser.

The R&S SMBV100A is Rohde & Schwarz’ first vector signal generator that uses Linux as its operating system, which helps to safeguard against viruses. Passwords can be set or the USB interfaces in the instrument can be disabled if necessary. The instrument also offers an optional removable 80 GB hard disk, which is useful for keeping critical data secure while being able to transport the instrument as required. This helps to avoid costly sanitizing procedures otherwise needed before an instrument can be removed from a secure area. If required, however, sanitizing can be performed easily.

The R&S SMBV100A also incorporates a convenient user interface that will be familiar from the company’s other signal generators. The block diagram enables intuitive operation while the integrated transient recorder (graphics block) enables visual monitoring of the signals that are generated (I/Q diagram, spectrum, constellation, CCDF, eye diagram, etc.). The context-sensitive online help facility provides useful background information about all setting parameters of the signal generator.

Conclusion

When designing a new all-round vector signal generator, the trick is to meet today’s requirements while also leaving room to satisfy future requirements and the R&S SMBV100A provides sufficient reserves. It combines the benefits of purely analog signal generators with those of a powerful vector signal generator. The instrument contains features that are normally only found in high-end signal generators (see Table 3). At the same time, it offers a good price/performance ratio. This is due to the three-year calibration cycle, the high-quality technical implementation and the user-friendly service concept that makes it possible to quickly repair instruments on-site if necessary.

Rohde & Schwarz, Munich, Germany,
+49 1805 12 4242,
customersupport@rohde-schwarz.com;

Americas: Rohde & Schwarz,
+1 888 837 8772,
customer.support@rsa.rohde-schwarz.com;

Asia: Rohde Schwarz,
+65 65130 488,
customersupport.asia@rohde-schwarz.com.

RS No. 302

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