Modern digital oscilloscope using dual trigger arrangement method
Triggering is key to playing a stable, repeating waveform on the screen, while also providing an effective tool for capturing one-off events. With the advent of digital oscilloscopes, triggering capabilities have gained many new extensions.
Most oscilloscopes offer an auxiliary trigger system or "B" trigger that allows the user to define a wider range of conditions. The B flip-flop waits for the main (Y) trigger to occur, and then triggers acquisition when its own edge threshold is crossed. The two can be used together to set up some fairly complex trigger conditions. For example, A may detect a glitch on the device clock input line and trigger B if a rising or falling edge is encountered on the output. Without this conversion, the glitches can be ignored. These two sets of conditions are used together to determine whether glitches can cause unwanted state changes.
Until recently, B trigger functionality has been limited to edge detection. But with complex new signal formats, especially those used in serial protocols such as PCI Express and Serial ATA, there is a need for a better match between the capabilities of the trigger system and the signals it is processing.
Errors in these fast new protocols can come from the combined results of multiple events such as logic states, offsets, transients, rise time issues, etc. Sometimes it is necessary to specify very precise ranges of conditions to identify elusive errors. This requires a family of trigger tools that can analyze more conditions. This problem can be solved using a dual trigger arrangement, where the B trigger system is essentially the same as the A system. It's just that in many cases, the A condition is relatively simple, while ideally, the B flip-flop should be able to evaluate a more complex set of indicators, such as the number of events that are only valid when other logic signals are in a specified state. However, related trigger B has always lacked the flexibility of the A trigger system. Therefore most oscilloscopes only provide a very simple B trigger.
