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distortion of CLK waveform after touching pads

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duet12

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Hi,

I am wondering if you have even encountered this kind of CLK distortion.

The circuit under test needs an Clock input, which is supplied from a voltage generator. The Clock output from generator is monitored through a oscilloscope.

The waveform of clock is distorted after the clock probe touch the pads, the waveforms look like the following picture:

9_1174518745.jpg



Do you know what is the reason for this kind of distortion?

Thanks

Duet
 

it may be due to impedance mismatch
 

impedance mismatch will introduce reflection wave, and original wave + reflection wave = ur measurement.
 

What i meant is the transfer of energy is not proper between the two systems.. If you see it is taking more time to to reach the maximum value ..so some sort of loading effect which is prohibhiting it to rise to its max value in a given time......
 

Your 'after' waveform does resemble an impedance mismatch, however it doesn't show the time scale.
Also, we don't know your cable length, or at which end of the cable you measured the waveform, or other unknown factors.
 

The resistance offered can create the distortion
 

Thanks for your inputs.

It did seems a impendance mismatch. We are using two cable to get a longer wire so we can reach the test vehicle. Maybe the two cables we are using have different impedence.
 

may be due to mismatch or the bond wire made some type of filter
 

Is your cable properly terminated? Your stair-step waveform looks like the driving end of an unterminated cable.

Mixing cable impedances will also cause some signal reflection (a smaller stair-step), unless you install something like an L-network or T-network or transformer at the junction.
 

put a 1k resistor in series with your output, use a 50Ohm coaxial cable to connect to your oscilloscope and set the scope input to 50Ohm.

What you see is due to impedance mismatch.
 

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