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Rise Time


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In Digital Systems, Rise Time Is Paramount

In the digital world, rise time measurements are critical. Your oscilloscope must have sufficient rise time to accurately capture the details of rapid transitions.

To calculate the oscilloscope rise time required for your signal type, use the following equation:

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 Oscilloscope Rise Time Required = Fastest Rise Time of Measured Signal ÷ 5
Rise Time
-Rise time characterization of a high-speed digital signal.

Notice that this basis for oscilloscope rise time selection is similar to that for bandwidth. As in the case of bandwidth, achieving this rule of thumb may not always be possible given the extreme speeds of today's signals. Always remember that an oscilloscope with faster rise time will more accurately capture the critical details of fast transitions.

In some applications, you may know only the rise time of a signal. A constant allows you to relate the bandwidth and rise time of the oscilloscope, using the equation:
Rise Time
-Fast edge rates coupled with long board traces can create high-frequency transmission line effects such as undershoot, overshoot and cross-talk. If left undetected, these signal anomalies can seriously degrade the proper functioning of a circuit.
- Bandwidth = k ÷ Rise Time
where k is a value between 0.35 and 0.45, depending on the shape of the oscilloscope's frequency response curve and pulse rise time response. Oscilloscopes with a bandwidth of < 1 GHz typically have a 0.35 value, while oscilloscopes with a bandwidth > 1 GHz usually have a value between 0.40 and 0.45.

Tektronix offers oscilloscopes with rise times to match applications that range from the slower rise times of TTL logic to today's fastest CMOS, ECL and GaAs logic. Our newest oscilloscopes deliver rise times down to 7 ps.
Logic Family Typical Signal Rise Time Calculated Signal Bandwidth
TTL 2 ns 175 MHz
CMOS 1.5 ns 230 MHz
GTL 1 ns 350 MHz
LVDS 400 ps 875 MHz
ECL 100 ps 3.5 GHz
GaAs 40 ps 8.75 GHz

-Some logic families produce inherently faster rise times than others, which may prove important in your selection of an oscilloscope.

Back to Selection Table
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