Hello, The DSO80204B and the DSO90254A oscilloscopes can definetly measure a 400ps rise-time signal.

Here is a good way to look at sample rate to BW:

First determine whether you are using a Gaussian- or flat-response oscilloscope. Then, depending on the accuracy you need, select the appropriate multiplier and multiply the maximum signal frequency (Fmax) by the multiplier to determine the required oscilloscope bandwidth. Finally, ensure that the oscilloscope has sufficient sample rate to achieve the required bandwidth without sampling alias errors. For example, to measure a 400 ps rise-time signal (20 to 80 percent) with a flat-response oscilloscope to an accuracy of 10 percent would require a (0.4 /400 ps )1.2 = 1.2 GHz bandwidth oscilloscope, with a minimum sample rate of 1.2 GHz x 2.5 = 3GSa/s. For example to measure a 400ps rise-time signal with a Gaussian response oscilloscope to an accuracy of 10% would require a (.35/400ps)1.3 = 1.137GHz bandwidth oscilloscope, with a minimum sample rate of 1.137GHz X 4 = 4.55GSa/s

Determine maximum signal frequency (Fmax) 0.5/Signal rise time (10%~90%) OR 0.4/Signal rise time (20%~80%) Determine oscilloscope response type Gaussian-response Flat-response Rise time/bandwidth relationship 0.35/bandwidth (0.4~0.5)/bandwidth Rise time measurement error Oscilloscope bandwidth 20 % 1.0 Fmax 1.0 Fmax 10 % 1.3 Fmax 1.2 Fmax 3 % 1.9 Fmax 1.4 Fmax Minimum sample rate 4 x bandwidth 2.5 x bandwidth

The DSO80204B and the DSO90254A oscilloscopes can definetly measure a 400ps rise-time signal.

Here is a good way to look at sample rate to BW:

First determine whether you are using a Gaussian- or flat-response oscilloscope. Then, depending on the accuracy you need, select the appropriate multiplier and multiply the maximum signal frequency (Fmax) by the multiplier to determine the required oscilloscope bandwidth.

Finally, ensure that the oscilloscope has sufficient sample rate to achieve the required bandwidth without sampling alias errors.

For example, to measure a 400 ps rise-time signal (20 to 80 percent) with a flat-response oscilloscope to an accuracy of 10 percent would require a (0.4 /400 ps )1.2 = 1.2 GHz

bandwidth oscilloscope, with a minimum sample rate of 1.2 GHz x 2.5 = 3GSa/s.

For example to measure a 400ps rise-time signal with a Gaussian response oscilloscope to an accuracy of 10% would require a (.35/400ps)1.3 = 1.137GHz bandwidth oscilloscope, with a minimum sample rate of 1.137GHz X 4 = 4.55GSa/s

Determine maximum signal frequency (Fmax) 0.5/Signal rise time (10%~90%) OR 0.4/Signal rise time (20%~80%)

Determine oscilloscope response type Gaussian-response Flat-response

Rise time/bandwidth relationship 0.35/bandwidth (0.4~0.5)/bandwidth

Rise time measurement error Oscilloscope bandwidth

20 % 1.0 Fmax 1.0 Fmax

10 % 1.3 Fmax 1.2 Fmax

3 % 1.9 Fmax 1.4 Fmax

Minimum sample rate 4 x bandwidth 2.5 x bandwidth

Regards,

Mark