A real-time oscilloscope has a free-running ADC. RTOs use digital triggers to record when the signal exceeds a threshold and therefore align the signals in time. RTOs rely on oversampling - the sample rate must be much higher than the maximum signal frequency. To generate an accurate view of the signal, many scopes will sample at three or even five times their maximum input bandwidth. 

A sampling oscilloscope relies on repeated signals. They only capture a single sample per trigger event and this sample is at least 40 ns after the trigger event itself. The individual samples from multiple trigger events are then recombined to build up a picture of the overall signal. 

A sampling scope cannot trigger directly on the signal itself and instead needs a separate trigger signal from an external source. Sampling scopes rely on accurate triggering to overlay the repeated signals so that even with a sampling rate significantly below the signal frequency, they can display an accurate version of the overall signal.

A PicoScope SXRTO triggers on the input signal, like an RTO. However, unlike most RTOs it uses an analog triggering circuit separate to the main signal path to determine when the trigger happens. Using this type of analog triggering is much more accurate than the digital trigger of an RTO. 

The result is a free-running ADC that is able to capture and store information before and after the trigger point, but with the huge bandwidth capabilities of a sampling oscilloscope. 

The PicoScope 9400A Series comprises Sampler-Extended Real-Time Oscilloscopes (SXRTO) available with up to 25 GHz bandwidth, ideal for capturing step transitions down to 14 ps and impulses down to 28 ps. The maximum sample rate is 5 TS/s using random sampling, which equates to a timing resolution of 0.2 ps. The use of random sampling means an SXRTO can capture pre-trigger information and does not require a separate clock input. As such, the hardware includes a built-in trigger circuit on every channel, up to 5 GHz when using divide mode. An external direct clock input can trigger on signals up to 5 GHz, while the prescaled input accepts signals up to 20 GHz. The jitter from this direct trigger is as low as 1.5 ps. In terms of vertical resolution, the wide ±800 mV full-scale input range is augmented by 10 mV/div to 250 mV/div digital gain ranges on up to four channels. An optional clock recovery circuit can output a recovered clock and data up to 11.3 Gb/s. 

The touchscreen-compatible PicoSample 4 software is packed with features to assist with the characterizing of everything from signals (eye diagrams, pulse/impulse characterization) to digital systems and even semiconductors. It comes pre-loaded with over 175 mask tests for common protocols including Ethernet, HDMI 1, PCIe, SATA and USB 2.0. The scope can store traces up to 250 kS long, shared between all active channels. The buffer memory is available on any of the three acquisition modes - real-time, random and roll. Four independent zoom channels let you closely inspect your data, with resolution down to 0.4 ps. Using your PC's monitor rather than a built-in screen means those zoom views can be enlarged as much as you need to see all the detail. You can also personalize the display by hiding menus and controls and adjusting the colors to suit your needs. All of the PicoSample features are included in the price, with no additional hidden costs.