The Tektronix MDO4000 Series is the first and currently the only oscilloscope on the market with a built-in spectrum analyzer. It gives users the ability to capture time-correlated analog, digital and RF signals for a complete system view of their devices. It combines both the time and frequency domains in a single screen so engineers can view the RF spectrum at any point in time to find sources of noise, or to see how the spectrum changes over time or with device state. This capability represents a powerful new way to solve complicated design issues quickly and efficiently.
Based on the Tektronix MSO4000B Mixed Signal Oscilloscope Series, the MDO4000 Series allows engineers to use their oscilloscope to look at the frequency domain rather than having to find and re-learn a spectrum analyzer. When both the RF channel and any analog or digital channels are on, the oscilloscope display is split into two views. The upper half of the display is a traditional oscilloscope view of the time domain. The lower half of the display is a frequency domain view of the RF input. Models are available with four analog channels with 500 MHz or 1 GHz bandwidth, 16 digital channels and one RF channel with either 50 kHz to 3 GHz or 50 kHz to 6 GHz frequency range and ³ 1 GHz capture bandwidth.
Figure 1 The upper half of the MDO4000 Series display shows the Time Domain view of the analog and digital channels; the lower half shows the Frequecny Domain view of the RF channel.
As shown in Figure 1, the spectrum displayed in the frequency domain view is taken from the period of time indicated by the short orange bar in the time domain view – known as the spectrum time. With the MDO4000 Series, spectrum time can be moved through the acquisition to investigate how the RF spectrum changes over time, correlated to the events monitored on the digital and analog channels in the time domain view. This can be done while the oscilloscope is live and running or on a stopped acquisition.
Frequency Alone is No Longer Enough
It is estimated that more than 38 percent of embedded systems designs now have a wireless interface. In 2011 alone, more than one billion wireless networking enabled products will ship to consumers. This means engineers are now troubleshooting embedded system designs with integrated wireless modules, requiring them to work in both the time and frequency domains.
With oscilloscope and spectrum analyzer functionality integrated into a single instrument, design engineers can now test multiple points of their design at one time, looking at their serial and parallel buses, digital and analog signals, and RF signals in a single glance to quickly and efficiently troubleshoot system problems. Prior to the MDO4000, engineers who needed this insight had to attempt to capture RF on their spectrum analyzer and analog/digital signals on their oscilloscope. Those acquisitions are not time-correlated and it can take days of trial and error to capture exactly what is needed.
Correlating Across Domains
The unique architecture of the MDO4000 Series provides a triggered acquisition system that is fully integrated with the RF, analog and digital channels. A single trigger event coordinates acquisition across all channels, allowing the user to capture a spectrum at the precise point in time where an interesting time domain event is occurring. A comprehensive set of time domain triggers are available, including edge, sequence, pulse width, timeout, runt, logic, setup/hold violation, rise/fall time, video and a variety of parallel and serial bus packet triggers. The RF power level of the RF input can even be used as a trigger source.
Because the MDO4000 Series captures a long time period of the RF signal, it can precisely calculate the RF spectrum at a specific point in time in the acquisition. This allows engineers to move spectrum time through their acquisition and see how the RF spectrum is changing in relation to their other signals.
Figure 2 The Spectrum Time display shows the frequency at 2.2202 GHz when the command arrives on the SPI bus, which tells the VCO/PLL the desired frequency.
A simple everyday application – tuning of a VCO/PLL – illustrates the value of connecting the time domain and frequency domain. Figure 2 shows what can happen during the turn-on of a VCO/PLL. In this case, Channel 1 in yellow is probing a control signal that enables the VCO. Channel 2 in blue is probing the PLL voltage. The SPI bus, which is programming the VCO/PLL with the desired frequency, is probed with three digital channels and automatically decoded. Initially, spectrum time was placed after the VCO was enabled and coincident with the command on the SPI bus telling the VCO/PLL the desired frequency. In Figure 3, spectrum time is moved about 250 µs to the right. At this point, the VCO/PLL has settled to its desired frequency of 2.3987 GHz.
Figure 3 Spectrum Time is moved 250 μs to the right, showing the final frequency that the VCO/PLL has settled on.
Key MDO4000 Features
The MDO4000 has a minimum RF capture bandwidth of 1 GHz. A FFT is performed on the acquired RF signal that can be converted to baseband I and Q vector data. This enables the MDO4000 Series to display three RF versus time traces on the time domain graticule derived from the data:
- Amplitude – The instantaneous amplitude of the RF input versus time
- Frequency – The instantaneous frequency of the RF input, relative to the center frequency versus time
- Phase – The instantaneous phase of the RF input, relative to the center frequency versus time
- Each of these traces may be turned on and off independently, and all three may be displayed simultaneously. RF time domain traces make it possible to understand what is happening with a time-varying RF signal and to easily measure system and RF latencies.
Figure 4 Automated peak markers identify critical information.
In a traditional spectrum analyzer, it can be a very tedious task to turn on and place enough markers to identify all the peaks of interest. As shown in Figure 4, the MDO4000 Series simplifies this process by automatically placing markers on peaks that indicate both the frequency and the amplitude of each peak. The criteria used to determine what a peak is can be adjusted by the user.
In addition to outstanding bandwidth performance, minimum 1 GHz capture bandwidth and excellent noise performance (DANL typical -150 dBc/Hz), there are many additional advanced features in the MDO4000 Series Spectrum Analyzer. Advanced functionality includes spectrogram display, manual markers, automated measurements for occupied bandwidth, channel power and adjacent channel power ratio. Like a typical spectrum analyzer, the MDO4000 Series offers four user configured or automatic traces or views of the RF input including normal, average, maximum hold and minimum hold. Detection types include +peak, -peak, average and sample.
Signal input methods on spectrum analyzers are typically limited to cabled connections or antennas. But with the optional TPA-N-VPI adapter, any active, 50 Ω TekVPI probe can be used with the RF input on the MDO4000 Series. This increases flexibility when hunting for noise sources and enables easier spectral analysis by using true signal browsing on an RF input.
Based on the industry-standard MSO4000B mixed signal oscilloscope, the new MDO4000 Series oscilloscope is the industry's first to incorporate a spectrum analyzer. While the ability to make RF measurements from one instrument is convenient for the user, the real power is in its ability to correlate events in the frequency domain with the time domain. Mixed Signal Oscilloscopes have transformed embedded systems debug by allowing correlation across analog and digital signals to become a must have tool on the bench. The Mixed Domain Oscilloscope category will likely experience similar acceptance as wireless becomes more commonplace and design complexity continues to increase.