Year of the mixed signal
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 6/1/2007 2:00:00 AM
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2007 isn’t half over, but I’m already declaring it “The year of the mixed signal.” Yokogawa, Tektronix, LeCroy, and Rigol introduced mixed-signal oscilloscopes (MSOs) or mixed-signal options for existing oscilloscopes this year. The four join Agilent Technologies in the MSO market.
Yokogawa was first with the DL9710L. Released in February, this instrument has four analog channels and 32 logic channels. In March, LeCroy countered with 18- or 36-channel logic options for its WaveRunner Xi and WaveSurfer Xs two- and four-channel oscilloscopes. (The company had previously offered a USB-based logic-analyzer accessory.)
In April, Tektronix reentered the MSO market when it introduced the MSO4000, which has two or four analog channels and 16 logic channels. Rigol’s four models in the DS1000CD series have two analog and 16 digital channels.
So many MSOs recently appeared because just about everything has an embedded processor, a field-programmable gate array (FPGA), an analog-to-digital converter (ADC), or a digital-to-analog converter (DAC). Devices that had previously relied on mechanical or analog control now use digital logic.
Applications for digital devices vary widely, from refrigerators to levelers that use lasers to align wall pictures. Popular applications include consumer products such as MP3 players and automotive engine controllers. Even power supplies include digital controls.
In many engineering labs, mixed-signal oscilloscopes eliminate the need for dedicated logic analyzers. “Engineers may have a logic analyzer on a cart and use it once in a while,” said Chris Lohberg, product manager at Tektronix, “but the oscilloscope is always on.”
Agilent has offered MSOs with 16 digital channels for several years. Yokogawa chose to double that number because, according to product manager Joseph Ting, many engineers are developing embedded systems with 32-bit processors.
LeCroy chose to offer 18 and 36 logic channels because “engineers working on 16-bit and 32-bit processors need the extra channels for clock and control signals,” said product manager Dan Monopoli.
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Mixed-signal oscilloscopes can decode serial data streams such as RS-232. Courtesy of Tektronix. |
Engineers who develop systems with parallel buses often use the “bundling” feature to simplify displays. With bundling, you can group signals into one “bus” and display the value in numerical format (usually hexadecimal). If you see an incorrect value, you can expand the bundled signal into its components and troubleshoot individual signals.
MSOs now include the ability to decode serial buses in addition to parallel buses. “MSOs combine an oscilloscope with a logic analyzer and a protocol analyzer,” said Ting. The ability to decode serial buses such as Inter-IC (I2C), RS-232, local interconnect network (LIN), and controller area network (CAN) is included in the latest mixed-signal oscilloscopes.
The figure shows an MSO decoding an RS-232 signal into its digital value. With their decoding capability, MSOs can now trigger an acquisition based on a serial-bus value. They’ve always been able to trigger on a parallel-bus value.
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