We’ve recently seen a number of announcements for single channel digital oscilloscopes. Some are configured like a (very large) pen. This is convenient, but the single channel is a real limitation.
A single channel scope can display one signal, so it can show you a signal at that point in the circuit: amplitude, frequency, waveform shape and so on. That’s certainly useful.
However, a large part of oscilloscope use is to determine the relationship between two or more signals. For example, when signal A transitions high, does signal B transition low? What is the time spacing between those two events? That information requires a two-channel display.
If two channels are good, are four channels even better? There are some measurement situations where four channels are useful, but this is more a matter of convenience than necessity.
Suppose you need to view three signals A, B and C and you have a two-channel scope. Then you could view and trigger from the A signal on channel 1. Then use channel 2 to view signal B and then signal C. You can see B and C individually and relate them back to signal A, so you can determine the time relationship between all three signals.
It is more convenient to have all four traces visible, but this creates other challenges: keeping track of which trace is which, and configuring the various display and triggering controls.
The cost of an oscilloscope is spread over different components: the analog front end, the digital and microprocessor section, the power supplies and the physical case. For a two channel scope, the additional cost is in the second analog front end. Given the additional utility of a two channel scope, we think it’s worth it. So, you may find an application where a single channel scope is fine. For general purpose circuit debugging, however, you’ll need a scope with at least two channels.