How to use the Tektronix MSO series oscilloscope for digital acquisition

There are two basic tasks when preparing for digital acquisition with an MSO Tektronix oscilloscope. First, as with a logic analyzer, the MSO digital channel gates need to be configured for the logic family being tested to ensure the correct logic levels are acquired. Second, the analog channel offsets need to be adjusted to achieve accurate time correlation between the analog and digital channels.

You can use the analog channels of a Tektronix oscilloscope to quickly check the logic swing of a digital signal. The Tektronix MSO can automatically measure the amplitude of a 5 V CMOS signal using measurement statistics from multiple acquisitions. For logic families with symmetrical voltage swings, such as CMOS, the threshold is half the signal amplitude. The Tektronix MSO can also set the digital channel threshold to 2.5 V, which is half the 5 V CMOS signal amplitude. However, for logic families with asymmetrical logic swings, such as TTL, you generally need to consult the component data sheet and use half of the maximum low-level input voltage value (TTL VIL = 0.8V) and the minimum high-level input voltage value (TTL VIH = 2.0V) of the logic device as the threshold (TTL Vthreshold = 1.4V).

In addition, the Tektronix oscilloscope sees the time offset between the rising edges of the analog and digital waveforms of the same signal. The analog waveform is ahead of the digital waveform. To accurately make measurements, the analog-to-digital time offset must be removed to achieve better time correlation between the analog and digital waveforms. The Tektronix MSO series of oscilloscopes provides adjustable analog probe deskew to align the analog channels relative to each other and to align the analog channels with the digital channels. The analog channel deskew setting compensates for the propagation delays of different analog probes. Each oscilloscope in the Tektronix MSO series of oscilloscopes comes with a logic probe. To simplify digital measurements, the oscilloscope compensates for the propagation delay of the logic probe, so there is no digital channel probe deskew adjustment. For example, the channel-to-channel skew specification for the digital channels of the MSO4000 Tektronix oscilloscope is typically 60 ps.