Mixed-domain oscilloscope
A Mixed-domain oscilloscope (MDO) is a type of electronic test equipment with the ability to capture time-correlated analog, digital and RF signals for a complete system view of the device under test. It provides the functions of a mixed signal oscilloscope(MSO), but also has a built in spectrum analyzer. It combines the time and frequency domains in a single screen so users 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.
Architecture
In August, 2011, Tektronix introduced the first MDO. Currently Tektronix is the only manufacturer producing these instruments.[1] Within the instrument is a fast-ADC-and-large-memory architecture, with one ADC providing the spectrum analysis using a digital signal processor, and another ADC providing traditional oscilloscope channels. With this architecture, the dedicated RF input provides the performance required for typical RF signals without requiring the other analog channels to equal that performance. Thus, adequate performance levels are achieved on both analog and RF channels while keeping the price of the instrument in line with a mainstream oscilloscope.
In addition, the dedicated RF input enables the use of optimized RF circuit elements, along with advanced signal processing techniques such as additive dither to improve linearity. These techniques cannot be used with a typical analog oscilloscope input because the use of some RF circuit elements could impact measurements down to DC, and the use of dither would be visible as noise in the time domain.
Use Model
When both the RF channel and any analog or digital channels are active, the Mixed Domain Oscilloscope (MDO) 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. The frequency domain view represents the spectrum acquired from the RF input.
In order to deal with the time-varying nature of modern RF signals, an MDO incorporates a triggered acquisition system integrated with the RF, analog, and digital channels. This makes it possible for a single trigger event to coordinate acquisitions across all channels. Time domain triggers can include Edge, Sequence, Pulse Width, Timeout, Runt, Logic, Setup/Hold Violation, Rise/Fall Time, Serial or Parallel Bus Packet Content, Video. RF input power level can also used as a source for Sequence, Pulse Width, Timeout, Runt, and Logic trigger types.[2]
Applications
With oscilloscope and spectrum analyzer functionality integrated into a single instrument, design engineers gain the ability to test multiple points of a particular system design at one time, looking at serial and parallel buses, digital and analog signals, and RF signals concurrently. Prior to the Mixed Domain Oscilloscope (MDO), engineers who needed this insight had to capture RF on a spectrum analyzer and analog/digital signals on a mixed-signal oscilloscope. Those acquisitions are not time-correlated and it could take significant trial and error to capture exactly the required information and additional effort to hand correlate data using spreadsheets.[3]
Applications for the MDO include system-level troubleshooting of designs with integrated WLAN, ZigBee or Bluetooth wireless modules, analyzing turn-on behavior of a VCO/PLL, and calculating latencies from control logic signals or serial bus commands to resultant RF changes.
See also
References
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