Mixed-signal DSOs offer four analog channels

Digital scopes that also provide logic-timing-analysis capabilities aren't widely available from the major benchtop-scope manufacturers. Among the best-known manufacturers, Agilent is the only game in town, and, until now, its highest performance offering was a unit from the compact 54620 series that provided two 500-MHz-bandwidth analog channels along with 16 timing-analysis channels. With the addition of three new MSOs (mixed-signal oscilloscopes) to the Windows-based Infiniium line, Agilent now offers a unit that, in addition to the timing-analysis channels, provides four 1-GHz-bandwidth analog channels (Picture). Moreover, you can outfit the new scopes with capture memories as deep as 8M samples/channel.

If you use only two analog channels, you can interleave the unused ADCs and memory to provide each active analog channel with capture memory as deep as 16M samples. The analog channels can then acquire signals at 4G samples/sec. The logic-channel memories are limited to 8M samples/channel, however, and the maximum logic-channel acquisition rate is 1G sample/sec. That rate is adequate for alias-free capture of logic signals that change state 1 billion times/sec. (At 1G sample/sec, the Nyquist frequency is 500 MHz, but each cycle contains two state changes.) Whether or not you interleave analog channels, the analog and logic channels always capture equal-duration records.

It would be nice if, with a total of 20 channels, the scopes could display more than their front-panel screens' standard 640×480 pixels. For now, though, a 640×480-pixel display is all you get—even if you connect an external monitor. Agilent says it is working on an upgrade and hopes that new Infiniium scopes will soon be able to drive external displays at higher resolution. Similarly, users must wait before their Infiniium scopes host Agilent's low-cost 1690A logic analyzer, which performs both state and timing analysis. Although Agilent offers a time correlator, which can time-align scope and logic analyzer displays, the Windows-based Infiniium scopes, unlike the company's open-architecture Windows-based logic analyzers, run only a short list of applications. Moreover, Agilent does not currently offer a product that uses one set of probes to simultaneously drive an MSO's analog and logic inputs.

On the plus side, the MSOs' designers have built in some new and useful display modes that the 546xxD-series units don't offer. For example, the Infiniium scopes can superimpose a hexadecimal display of bus data on timing waveforms, often making it possible to reduce the number of channels on the screen. Infiniium MSO prices begin at $15,995. A unit with four 1-GHz-bandwidth analog channels and 8M samples/channel of memory (16M samples/channel interleaved) costs $31,495.