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Adeas invests in high-end spectrum analyser |
Adeas has recently invested in a Rohde & Schwarz, FSU series, high-end spectrum analyzer. We decided on the FSU to facilitate the growing demand of the Adeas development lab to measure and validate higher signal specifications of electronic designs.
Among other products, Adeas develops electronic modules that generate a modulated RF signal. For instance digital TV signals like DVB-C(2) and DVB-T(2). The demands on signal quality of these modules are higher than can be measured with more main stream spectrum analyzers. It’s only with a high end analyzer of renowned brands like Agilent en Rhode en Schwarz that this becomes a possibility.
Background
In modulator development Adeas uses FPGA’s because of the strong increase in the number of logical blocks and internal clock speed of these components in recent years. The high speed digitization enables designers to implement a larger portion of the signal path in FPGAs and eliminate analog disturbance and imperfections. Although the latter are replaced by some challenges in the digital domain in general the digital signal processing helps to achieve an improved signal quality of the analog output.
But not every aspect can be digitized, for instance an oscillator and D/A converter remain necessary. These components have a very large impact on the analog signal quality of the module output. Of major influence on signal quality are phase noise and design aspects like crosstalk, decoupling and other unwanted disturbance.
The signal quality or specifications of the generated output signal can be measured with a dedicated instrument for a specific standard. These instruments are protocol or signal analyzers. But with the right knowledge and high end equipment not only the output signal can be measured but also the intermediate signals in the design. So not only the output signal as generated by the DAC but also the oscillator and the PLL generated signals.
The FSU series spectrum analyzers by Rohde & Schwarz have a large dynamic range, low DANL (displayed average noise level) and low phase noise and are therefore very suitable for measuring the characteristics of DVB modulators. The model bought by Adeas also has the phase noise option installed which enables easy phase noise measurements.
An instrument with a large dynamic range is important to be able to measure noise and spurious signals in neighboring frequency bands of the modulated signals. This is a important specification in modulators since noise in neighboring channels reduces signal quality of the modulated signal in these channels.
Bear in mind that modern modulation methods like QAM and OFDM have a high Crest factor which raises the bar on large dynamic range even further.
The phase noise of the oscillator in a modulator is of major influence on the eventual BER (bit error rate) of the output signal. If the phase noise is below a certain level than the BER will also be below the related level and therefore result in better specifications. Instead of measuring the BER with a specific TV analyzer, we can measure phase noise of the unmodulated carrier. By doing this the cause of higher than expected BER can be determined which can be invaluable in the development and qualification process.
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