you will need a pretty good idea of what signals you’re going to need to look at: whether (analog) audio and transducer signals or (digital) pulses and steps. If you’re looking at digital signals, will you be measuring rise times, or just looking at approximate timing relationships? Will you use the scope to qualify elements of your design, or mostly for debugging? Either way, accurate signal capture at the outset is more important than any later signal processing – your decisions rely on accurate information, and you can always process the information on a computer.

you need to consider not just your present generation of designs, but future generations too. A high-quality scope will give you many years’ reliable service.

Ensure that all the parameters you need to measure are detailed as “guaranteed specifications” in the oscilloscope datasheet. Parameters listed as “Typical” are simply an indication of oscilloscope performance, and cannot be used to make meaningful measurements that comply with recognised quality standards

High-speed digital, serial communications, video and other complex signals can therefore require scope bandwidths of 500 MHz or more.

When selecting bandwidth, use the ‘five times rule’. If bandwidth is too low, your oscilloscope will not resolve high-frequency changes. Amplitude will be distorted. Edges will vanish. Details will be lost.

TTL and CMOS may need 400 to 300 ps rise times.

Many logic families have faster rise times (edge speeds) than their clock rates suggest. A processor with a 20 MHz clock may well have signals with rise times similar to those of an 800 MHz processor. Rise times are critical for studying square waves and pulses. Square waves are standard for testing amplifier distortion and timing signals for T vs and computers. Pulses may represent glitches or information bits – too slow a rise time for the circuit being tested could shift the pulse in time and give a wrong value.

When selecting a mid-range scope choose probes with capacitive loadings of < 10 pF. The best passive probes offer 1GHz bandwidth with a capacitive load <4 pF.

To start with, select passive probes that have high bandwidth and low loading. Active ground-referenced probes offer 1 to 4 GHz bandwidth, and differential active probes 20 GHz or more. Adding a current Probe enables the scope to calculate and display instantaneous power, true power, apparent power, and phase. High voltage probes measure to 40 kv peak. Specialty probes include logic, optical and environmental types.

Isolated channels simplify floating measurements. Unlike ground-referenced oscilloscopes, the input connector shells can be isolated from each other and from earth ground.

The more time-correlated analog and digital channels your scope has, the more points in a circuit you can measure at the same time and the easier it is to decode a wide parallel bus, for instance. The example shows 2 analog, 8 digital and 1 decoded bus waveforms.

The faster you sample, the less information you’ll lose and the better the scope will represent the signal under test. But the faster you will fill up your memory, too, which limits the time you can capture.

Nyquist said that a signal must be sampled at least twice as fast as its highest frequency component to accurately reconstruct it and avoid aliasing (showing artefacts that are not actually there). Nyquist however is an absolute minimum – it applies only to sine waves, and assumes a continuous signal. Glitches are by definition not continuous, and sampling at only twice the rate of the highest frequency component is usually not enough. Conclusion: A high sample rate increases resolution, ensuring that you’ll see intermittent events.

Communications triggers: embedded system designs use both serial (I 2 C, SPI,CAN/LIN, USB …) and parallel buses.

Triggering lets you isolate a group of waveforms to see what is going wrong. Specialized triggers can respond to specific conditions in the incoming signal making it easy to detect, for example, a pulse that is narrower than it should be.

To search for infrequent transients such as jitter, runt pulses and glitches, select at least a mid-end scope that combines long record length with a high waveform capture rate.

Capturing enough detail to decode this USB serial data stream requires high resolution sampling (200ps). Capturing multiple packet contents needs a long time (200µs). An oscilloscope with long record length (1 Mpoints) is needed to display both.

Advanced search lets you define various different criteria, similar to trigger conditions, which will be automatically detected and marked in the captured waveform.

The industry’s fastest tool for automated navigation, search and analysis is Wave Inspector ® , a proprietary technology. It allows you to specify search criteria to automatically find every occurrence in an acquisition that violates some specified criteria such as setup and hold time

Scalars, with user-adjustable variables and results of parametric measurements.

Once again, extra functions shorten the time to answer. Digital Signal Processing techniques can automate measurements – making them faster, more accurate and more repeatable than is possible with cursors. you can even write your own formulae for specific maths functions.

Others include optical communications, memory system verification, communications standards testing, disk drive measurements, video measurements, and more.

Complex electronic designs are driving innovation across many industries today. your scope should have all the features your application needs – now and in the future.

There should be support for your own language, with templates for the dials.

Oscilloscopes should give you different ways to operate the instrument. Built-in help can provide a convenient, built-in reference manual, while smart menus give easy access to multifunction, context-sensitive commands.

Software to control the scope from your PC, take automated measurements, waveform data logging and export waveforms live.

video port to export the oscilloscope display to a monitor or projector