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Modular scalable test set comprises source-measure ATE

Posted: 16 Mar 2005 ?? ?Print Version ?Bookmark and Share

Keywords:series 2600? system sourcemeter? keithley? dmm? adc?

While discussing this new Series 2600 System SourceMeter with Keithley product marketer Andy Armutat, he pointed out that the 2600!essentially a DMM for semiconductor test!uses patented ADCs. These are really what endows the instrument with the ability to do simultaneous current and voltage measurements. The third-generation technology that's referred to in the company's press statement is largely about these ADCs.

Note too that there are dual ADCs involved; one per channel (one for I and one for V). These run simultaneously, providing the box's fast source-readback capability. Armutat emphasizes that these ADCs provide throughput rates of less than 80?s, or 12,600 readings/s. The source-measure also does 210?s/point source-measure sweeps, or 4750 points/s.

The A/Ds also offer programmable integration rates, letting you optimize operation for either speed or resolution (up to 24 bits).

Series ranging
That kind of speed and programmability really differentiates this instrument, but there's more to it than raw speed. The 2600 also makes use of a streamlined series (vs. parallel) ranging topology (it's patent-pending), to get low-glitch operation that fast-ranges, with outputs that rapidly settle.

So, what else is significant about these new 2600s? That involves looking a bit more closely at the problems they address. The lack of optimized testing schemes for multi-channel source-measure applications is forcing some folks to choose among high-power and expensive mainframe-based systems, or slow instrument-based systems. Alternatively, you can build up fast instrument-based systems, but they're typically complex.

As an example, let's look at a typical system comprised of discrete instruments. A 3A precision power supply might cost about $1,000, and a current source (such as Keithley's Model 6220) would add about $3,500 more. Throw in a precision 5-1/2-digit DMM, and add about $700 to the bill.

But wait. There's more. Our hypothetical source-measure system isn't complete yet. We need a low-frequency arbitrary waveform/pulse generator. That costs about $1,500, and don't forget a dynamic electronic load that adds another $1,500. Finally, a trigger controller would top off the mix of this typical system, adding about $500 more to the tab. That's a grand total of $8,700! You can get a single-channel Keithley Model 2601 SourceMeter for less than $5,500.

A hardware, software mix
Armutat emphasizes that a 2600 can lower the cost of test by means of the innovative A/D hardware, as well as unique software and firmware. He emphasizes how Keithley's TSP-Link (Test Script Processor Link), for example, lets multiple SourceMeter instruments be controlled as a single unit. "It's very flexible," he says.

"You can configure a modular 2600 as a precision power supply," says Armutat, "or as an ARB (arbitrary waveform generator), or as a pulse generator, to name just a few. When you do that you get a source-measure unit at a very reasonable cost per channel, on the order of 35 to 75 percent less."

Not mentioned in the press statement is the fact that the 2600's TSP-Link and Test Script Processors!two new Keithley-developed technologies!also make it possible to scale the size of a Series 2600 system from one channel to as many as 128 channels.

Eliminating the need for a chassis or mainframe also gives TSP-Link the flexibility to scale a system's channel count up or down as your application demands. That can be another key element to cost-effectiveness.

Beyond that, any single-unit or multi-unit system can be programmed to run a single high-speed test sequence (an embedded test script) on the Test Script Processor. "You can run independent of a PC, too," adds Armutat, "yet interface with component handlers and probers. TSP eliminates communications bottlenecks between your PC and instruments."

In operation, any 2600-based system can run embedded test scripts on a master unit's TSP. Test sequences are processed and run on embedded computers in the 2600, rather than on an external PC controller. That eliminates delays due to possible IEEE-488/GPIB communications link congestion. In fact, Armutat claims TSP test scripts will provide throughput gains of up to ten times those of PC systems controlling instruments using GPIB.

Moreover, a single TSP test script, running on a master unit, can control all SourceMeter channels in a system, and acquire data from any Series 2600 instrument connected to the TSP-Link, which supports connections for up to 64 Series 2600 instruments. Scripts support instrument command queuing, use of modular sub-routines with passable parameters, and Pass/Fail and limit testing.

Scripting can also support lots of math operations, and branching and looping, as well as external triggering, intelligent digital I/O read and write, and RS-232 communication.

"You can also create custom source-measure parameters for specific characteristics," says Armutat," such as dynamic impedance for transistor testing. This kind of capability has never been accessible before at this price level."

Freebie curve tracing
In the company's press release, brief mention is made of Keithley's freebie LabTracer 2.0 software for the 2600 instruments. In use, LabTracer 2.0 handles things such as curve tracing and data acquisition, providing a graphical user interface for instrument setup. Supporting up to eight 2600s or Keithley's earlier Series 2400 SourceMeters, data is provided in spreadsheet format (so it can be exported to Excel), or as a graphical format file.

Similarly, Keithley's free TSP Builder tool for automated test development also helps you create, modify, and debug TSP test scripts. "It's for both lab users and production users," notes Armutat. "Using TSP Builder, you need just a half dozen steps to create or modify a test script for the instrument to execute.

"First," says Armutat, "TSP Builder detects any 2600 box connected to a system's GPIB bus at startup. Then it opens a test script. Nest you would edit the code. The script is automatically transferred to the instrument and compiled when it's saved in TSP Easy.

"Then you select Run and execute the test script. Any error messages, return data, or debugging cues will show up in a window. Once the test script is complete, it can be called from any test program, or it can be executed directly in the TSP Easy software."

In summary, a 2600 Series instrument can control sourcing, measuring, pass/fail decisions, test sequence flow control, component binning, and data storage!and do it for less than assemblages of separate test gear.

When you consider that a dual-channel Model 2602 SourceMeter sells for less than $8,000, that seems like a pretty good deal that's worth investigating further.

- Alex Mendelsohn

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