An oscilloscope’s trigger function is important to achieve clear signal characterization, as it synchronizes the horizontal sweep of the oscilloscope to the proper point of the signal. The trigger control enables users to stabilize repetitive waveforms as well as capture single-shot waveforms. By repeatedly displaying similar portion of the input signal, the trigger makes repetitive waveform look static.
Oscilloscopes offer various types of trigger functions, with edge triggering is the most basic and common type. Just like edge triggering, threshold triggering, is another type of trigger function that is offered both in analog and digital oscilloscopes.
Digital oscilloscopes, however, feature numerous specialized trigger settings not otherwise available in analog oscilloscopes. These triggers enable users to easily detect, for instance, a pulse that is narrower than usual. Such a condition would not be detected by a voltage threshold trigger only.
Advance trigger controls allow users to isolate events of interest to enhance the oscilloscope’s record length and sample rate. Some oscilloscopes even offer advanced triggering capabilities with highly selective control, allowing users to trigger on pulses defined by time (such as glitch, pulse width, setup-and-hold, slew rate and time-out), defined by amplitude (runt pulses), and delineated by pattern or logic state (such as logic triggering).
Pattern lock triggering is an advanced trigger function that offers NRZ serial pattern, triggering a new dimension by allowing the oscilloscope to take simultaneous acquisitions of a long serial test pattern that feature outstanding time base accuracy. This kind of triggering function can also be used to eliminate random jitter from long serial data patterns.
Other advanced triggering functions include serial pattern triggering, A&B triggering, trigger correction, search and mark triggering, parallel bus triggering and serial triggering on specific standard signals.
Serial pattern triggering can be utilized to debug serial architectures. It triggers on the NRZ serial data stream with integrated clock recovery while correlating event across the link and physical layer. The device can identify transition, recover clock signal, and allow users to set the particular encoded words for capture by the serial pattern trigger.
Unlike traditional oscilloscopes, which offer multiple trigger types on a single event only, modern oscilloscopes nowadays provide advanced trigger types on both A and B triggers. They also offer logic qualification that controls when to view the events, as well as reset triggering to start the trigger sequence again after a particular state, time or transition, enabling the oscilloscope to capture events of complex signals.
Since data and trigger acquisition have different paths, there is an inherent time delay between the data acquired and the trigger position, which result in skew and trigger jitter. This is where the trigger correction system comes in. By adjusting the trigger position, the system compensates the delay between the data acquisition path and trigger path, effectively eliminating all trigger jitter at the trigger point.
Search and mark triggering allows users to simultaneously scan for multiple events and mark those that meet the user’s search criteria, while parallel bus triggering enables users to save time by automatically decoding bus content.
Finally, some oscilloscopes can also trigger on specific kinds of standard serial data signals that include CAN, I2C, LIN, SPI and others.
Rich Markley says
The logic triggering capabilities of modern oscilloscopes are really impressive. Not only can you trigger on specific logic patterns, but also on logical combinations. That is to say that you can set up the oscilloscope to perform AND, OR, NAND, or NOR calculations on different combinations of logical inputs and trigger the oscilloscope when these conditions are met. This feature is especially useful in verifying the operation of digital logic.