Electronic Design

Entry-Level Oscilloscopes Serve Mixed-Signal Applications

While oscilloscopes remain the instrument of choice for embedded designers, today’s design environment demands that scopes bring more to the table than their traditional function of signal visualization. With all manner of systems from inexpensive childrens’ toys to high-end computers incorporating serial buses which carry complex signal content, designers are coming to expect more from their bench instruments, particularly in the realm of debugging of serial buses and mixed-signal circuitry.

To meet the needs of embedded system designers, Tektronix has launched its MSO/DPO2000 Series scopes, which sit in a market slot that has been unfilled to date. At the lower end of the market are instruments aimed solely at signal visualization with very little signal-debug capability. At the higher end there are much more capable instruments for sure, but buyers of such scopes may find themselves with a surfeit of bandwidth and a deficit budget to match.

The MSO/DPO2000 Series fills that hole between the low and high ends of the scope market, bringing sufficient bandwidth (but not too much), and a highly capable suite of mixed-signal debugging tools (see the photo). These scopes start at just $2580 each, so they won’t bust budgets. Within the series are two subgroups, the mixed-signal (MSO) and digital-phosphor (DPO) scopes.

The debug challenges of serial buses take engineers well beyond simple signal visualization. Engineers must determine whether hardware/software interactions are correct and whether system noise is affecting the bus, particularly from a timing standpoint. Packet contents must be confirmed as they traverse the bus from chip to chip as well.

To properly debug serial buses, designers have to manually count each bit, determining along the way if the bits are ones or zeroes. Then this data must be converted to understandable formats, such as hex values. The MSO/DPO2000 scopes automatically handle both triggering and decoding for all common serial communications standards. They also sport the ability to display two buses at once on the display, such as an I2C and serial-peripheral-interface (SPI) bus.

Debugging is aided by the scopes’ bus view, which color-codes elements of the packet to make them easily distinguishable. The scope also tells the user if the packet is a read or write and which address it is being sent to. Data values are shown in yet another color, and the scope provides an end-of-packet marker. The scopes can trigger on specific packet-level content, allowing users to set up a trigger for a specific packet of interest. They can search and mark all packet content for particular reads or writes. Data can be viewed in event-table format with time stamping of packets. Supported serial buses include SPI, I2C, RS-232, CAN, and LIN. It’s more than decoding.

For mixed-signal debugging, the scopes have 16 digital channels fully integrated into the instrument. These channels are integrated into the scope’s signal-acquisition front ends, enabling users to trigger on the same kinds of signal elements as on analog channels. Users can set up a combination of analog/digital channels, or set up parallel channels. All of the scopes’ search capabilities also work on the digital channels. Sample rates are up to 1 Gs/s for digital channels when using the first pod of eight channels; using more than that drops the sampling rate to 500 Ms/s.

The scopes perform time correlation of analog and digital channels, allowing viewing of up to four analog, 16 digital, and two bus time-correlated waveforms. This can be useful for examining the input and output of a digital-to-analog converter, or DAC, for example.

The MSO2000 and DPO2000 Series of oscilloscopes each consist of three models ranging from 100 to 200 MHz, with two or four analog channels. They offer USB plug-and-play PC connectivity and a 7-in. widescreen bright TFT display. All models contain 1M points of record length on each channel and a 1-GS/s sampling rate on all channels, ensuring at least 5X over-sampling of the signal. Additionally, the new models provide a capture rate of 5000 waveforms per second to aid discovery of transient events.

Prices range from $2580 for a two-channel, 100-MHz DPO2012 to $5150 for a four-channel, 200-MHz MSO2024. All models are available immediately from stock.

Tektronix
www.tektronix.com

TAGS: Components
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