The continued expansion of the IoT and the accompanying RF integration challenges mean that designers benefit from versatility across disciplines. A single product routinely combines RF, digital and analog design elements, meaning engineers need to interactively debug systems that include both RF and embedded subsystems. To address complex debugging issues with flexibility and value, RIGOL combines the latest real-time spectrum analysis with embedded debugging in multi-domain systems.
RIGOL’s multi-domain analysis combines the power of our new real-time spectrum analyzers (RTSA) with our high performance oscilloscopes to make investigating, correlating and analyzing signals easier than with traditional instruments. Unlike many of the basic RTSAs on the market, RIGOL’s RSA series all have a combination of hardware triggering and IF outputs designed to work with an oscilloscope for advanced multi-domain analysis.
INVESTIGATE
Identifying issues starts with capturing and verifying signals either in the time domain or RF domain. One of the advantages of this multiple instrument approach is how easy it is to view signals, by either time or spectrum. When symptoms appear in the RF transmissions, use real-time to monitor frequency, using seamless capture capabilities to analyze the characteristics of the signal. Extend this analysis into the time domain with the power versus time view or by monitoring the IF signal on an oscilloscope. Deep memory and waveform recording verify signals as they change on longer time scales. Use the real-time analyzer to investigate transient, high speed events. One of the most important views of a real-time signal is the density view. Density view highlights transient signals that are difficult to capture using other techniques by showing the probability of occurrence in color (see Figure 1). Density view makes it possible to differentiate signals, even when one is obscured by the spectrum of the other.
Figure 1 Density view of a hidden signal artifact.
Figure 2 Density view of a hidden signal artifact.
The real-time visualization modes can capture any RF errors and investigate how they change over time. As a debugging tool, RIGOL’s RSA enables viewing time in three distinct modes: Density shows time as probability of occurrence. Power versus time shows time domain signals, and the spectrogram shows a history of power across the spectrum (see Figure 2). The figure shows a signal with hopping FSK modulation. The image in the top center shows the 1 ms repetition rate of the transmission, the spectrogram on the left shows the hopping sequence and the spectrum in the bottom panel shows the latest capture of the FSK pulse, to determine power and frequency characteristics. Each of these RF pulse widths are less than 2 µs. To zoom in on their time domain activity, connect the scope to the IF output, which enables viewing the precise timing of the RF pulse to see it in context of other signals.
CORRELATE
There are three ways the RSA and an oscilloscope, such as the RIGOL 4000 series, can be used to correlate signals. For all three methods, first connect the RSA and the oscilloscope. The RSA trigger out is connected to either the external input or a standard channel. The oscilloscope’s trigger output is connected to the RSA trigger input. Finally, the IF output is connected to a scope channel in 50 Ω mode.
The first method involves triggering on the oscilloscope itself. With the RSA in real-time mode, select a view and trigger on the scope channel connected to the RSA IF output. The scope can be set to trigger on RF power changes and correlate RF with other signals on the scope display. The IF output down-converts the real-time center frequency to 430 MHz. In the second method, the RSA triggers with the scope, making correlated visualization of the spectrum possible whenever the scope identifies a trigger event. In this mode, basic visualization of the spectrum can also be done with the FFT math function on the oscilloscope. For more complex RF signals, use the third triggering method. This takes advantage of the real-time capabilities to trigger on the power level or specific values within the spectrum. Set the RSA trigger mode to power or frequency mask trigger, enable the RSA’s trigger out and use this signal to trigger the scope. This allows viewing the status of embedded, power and serial signals at the time of an RF event or EMI emission. The frequency mask trigger used to capture a FSK pulse is shown in Figure 3.
Figure 3 Display using frequency mask trigger mode.
Figure 4 Using 4000 series scope capture reveals a glitch in the center of the mask, captured in a recording of frames.
ANALYZE
With a deep memory scope like the 4000, the long record length enables viewing the time before and after an RF event to find the root cause. This time-based analysis is critical, since many causes are not instantaneous, rather a result of a previous event. Programmable components like FPGAs hide many of these errors. One way to debug and verify their performance is to monitor changes over time in a continuous dataset, to locate the logic or state error. RIGOL’s waveform record mode is another powerful tool for multi-domain analysis. Record mode makes it possible to capture a sequence of thousands of trigger events, followed by playing back and analyzing these frames using pass/fail masks or a point-by-point RMS difference analysis. Comparing occurrences of errors and establishing a common cause is critical to ultimately fixing the underlying cause. Figure 4 shows capturing the IF pulse (in purple), with the RSA trigger channel 1, shown near the bottom of the display.
CONCLUSION
The RSA series RTSAs from RIGOL are configured to make it easy to bring real-time visualization to multi-domain debugging. Used with a RIGOL MSO4054 oscilloscope or a 500 MHz mixed-signal oscilloscope already on the bench, the RSA bridges the gap between RF and embedded signals, making true multi-domain analysis possible. Multi-domain analysis includes time-correlated RF and embedded signals, configurable triggering across signal types and real-time visualization of the RF signals, saving engineers both time and money.
RIGOL
Beaverton, Ore.
www.rigolna.com