Like an octopus, the oscilloscope on today's design bench must sprout multiple tentacles, reaching out to monitor signals in many parts of a circuit and displaying the measured values all at once—with all events synchronized to a common time base. But with the increasing prevalence of both analog and digital signals in new designs, getting to the heart of a problem quickly and effortlessly has never been more critical.
Also, designers often need to capture events in real time, then scroll through to find where a glitch or other anomaly is stifling performance. That means huge memories. In digital designs, discerning a "high" from a "low" is simply no longer good enough. So oscilloscopes with multiple inputs, on-board data processing, and mixed analog/digital analysis capabilities are a must.
It turns out that oscilloscopes are edging closer to fulfilling these requirements. The digital storage oscilloscope (DSO) has become indispensible. In addition, many oscilloscopes have become de facto PCs and, therefore, highly capable of performing many computations on their own—with the ability to communicate.
A recent example of these trends is the Agilent Technologies 54642D mixed-signal, deep-memory scope (Fig. 1). It's called mixed-signal because it can measure and display two analog and 16 digital channels with all 18 channels time aligned. Consequently, it combines a scope's detailed signal-analysis capability and a logic analyzer's multitiming measurements. Intended for designs with lots of digital signals, it lets users view the complex interrelationships among all displayed signals.
Therefore, the 54642D is well suited for mixed-signal developmental projects, like cell phones, where the input and output to the user is analog while much of the signal processing occurs in the digital domain. Each of its analog channels provides 500 MHz of bandwidth. Its standard acquisition memory captures up to 8 Mbytes. The high-definition display is mapped into 32 levels of intensity that instantaneously disclose subtle details.
Powerful Triggering Necessary: Viewing analog and digital channels on a single instrument requires powerful triggering. When working with mixed analog and digital designs, it's sometimes difficult to trace an anomaly back to its cause unless the user can trigger on it and correlate it with another trace.
Consider a situation that employs the serial I2C (inter-integrated circuit) protocol as a communication channel. I2C is popular because it needs only two I/O lines for full implementation. However, along with the benefits of using two I/O lines comes the hassle of a complicated protocol. So a tool on the bench that eases I2C troubleshooting is certainly a benefit.
If the designer is working with microcontrollers that use PC serial communications, the 54642D's I2C bus trigger mode can be employed to first verify inter-IC communication handshaking. Then the I2C trigger can be used again to ensure that correct data is being transmitted to the desired device. Other triggers provided with the 54642D include CAN, USB, and SPI.
In summary, the deep memory capability on this mixed-signal oscilloscope (MSO) accelerates troubleshooting and verification. It permits the user to see slow analog and fast digital signals simultaneously and sustains a high sample rate, providing excellent resolution. The high definition realized, in turn, makes it easy to view subtle details that the deep memory captures, while serial triggering makes it possible to locate complex data patterns.
In the past, collecting data and transforming it into some type of desired format was a cumbersome job. But Gould Instrument Systems has streamlined this task and automated it in the Ultima 500, bringing the benefits of a sophisticated PC to a high-performance oscilloscope. This DSO provides 500-MHz bandwidth at the probe tip and a 2-Gsample/s sampling rate with 1 million points of data storage per channel. Internal floppy and hard drives—coupled with high-speed 100-Mbit/s Ethernet, USB, and PCI connectivity—enable virtually unlimited data storage and flexible communication. Users can easily transfer data to other computers (Fig. 2).