Digital communications systems are rapidly evolving today, calling for test equipment that can meet the new challenges they present. An important component of such test equipment is a flexible baseband source that allows development and production tests to be performed on state-of-theart receivers for a variety of standards. A self-contained baseband source must fulfill a wide range of signal requirements. Plus, it needs variable digital and analog outputs in order to directly operate the DUT. Used as a modulation source for vector signal generators, the R&S AFQ100A provides I/Q signals that offer all the sophistication of modern communications standards for generating the required RF signal.
Broad scope of applications
Outstanding signal quality
Connectors and operation
Features Analog signal output with unsurpassed specifications
A universal I/Q source must provide high signal quality. With its optimized design and state-of-the-art components, the R&S AFQ100A achieves a spurious free dynamic range (SFDR) of typ. 83 dBc.Today, new digital systems are developed with ever larger bandwidths, which makes the frequency response of such broadband signals especially interesting. This is where the R&S AFQ100A really excels, since it features a very high linear frequency response of typ. 0.05 dB.
However, even unrivaled baseband performance does not guarantee a flawless RF signal, since impairments can affect the signal quality by the time the signal is output. The R&S AFQ100A features a variety of functions to minimize the effect of these impairments, including its capability to compensate for the magnitude and phase of a non-ideal frequency response (e.g. of an external I/Q modulator) by means of settable filters. In this case, data can be measured by an external program and transferred to the F&S AFQ100A. During output, a matching inverse filter is taken into account in the signal, achieving a linear frequency response and optimum sideband suppression throughout the entire system.The R&S AFQ100A also provides I and Q compensation capabilities for each channel for level offset, delay and gain. Thus, in addition to being able to compensate for delays and effects due to external cables or other inserted elements, you can vary them on purpose in order to test receiver performance.
Optimal memory utilization
In addition to an excellent analog frontend, the R&S AFQ100A offers special memory features. The readout speed of data from the internal memory is user-selectable and can be optimally adapted to the useful signal internally. The R&S AFQ100A digitally converts the I/Q samples to the higher clock rate of the converter in realtime. This loss-free resampling makes it possible to implement a fixed clock rate for the D/A converter and an optimally adapted anti-aliasing filter, providing ideal signal characteristics. Furthermore, resampling allows you to read out data at a theoretical minimum clock rate, an advantage that means maximum signal duration using a specific memory depth.Memory management in the R&S AFQ100A provides yet another advantage: a granularity of 1. In other words, the waveform can always be output in a continuous cycle, no matter how long it is. Previously, you had to perform complex conversions for generating the correct signal length. You can now select any signal length without having to take into account multiples of possible memory granularity.
The memory depth of the R&S AFQ100A permits further applications such as the multisegment waveform function, which allows fast switchover between different signals. The special feature is that several different waveforms are already loaded into the memory, making it unnecessary to reload waveforms from the internal hard disk or an external controller.Various output modes support very fast switching times and seamless transition between the different segments of the multisegment waveform. This makes phase-continuous transition possible, which helps to avoid resynchronization when testing receivers.
Differential and digital I/Q outputs
Since modern baseband components are often equipped with differential inputs and outputs, the R&S AFQ100A also comes with differential outputs as standard. Of course, it is also possible to switch to the classic unbalanced I/Q output. In addition, the generator allows a DC voltage (bias) of up to ±2.5 V to be added to the differential output signal.
Both operating modes permit flexible level setting. However, to achieve a good signal-to-noise ratio at lower levels as well, the R&S AFQ100A is equipped with switchable attenuator pads. This enables continued use of the entire dynamic range and then an analogous attenuation of the level by max. 21 dB. As a result, the R&S AFQ100A provides high signal quality not only at an ideal level value but also across a wide level range.In addition to the flexible analog outputs, the R&S AFQ100A can optionally be equipped with two digital outputs. The first is a 68-pin HD-SCSI connector that outputs the digital I and Q signals in a common LVDS format at a maximum resolution of 16 bit each. This output supplies the data, including the clock signal, directly from memory. D/A converters can thus be ideally operated as DUTs. The second output provides the digital signals in accordance with a proprietary Rohde & Schwarz standard, which makes the R&S AFQ100A ideal for operation in combination with other equipment from Rohde & Schwarz.
Versatile yet easy to operate
Although the generator’s hardware is concealed in a black box, you can easily access its software. The R&S AFQ100A features a modern graphical user interface that can either be controlled directly via an external display, mouse and keyboard or easily transferred to any computer in the network via Windows XP Remote Desktop (via LAN) and operated from there.Remote control via SCPI commands is also available.