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Rise time / Fall time

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balajykumar

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could anyone say what is the impact of the Rise time/Fall time of the device not match? exlpain the impact in the functionality wise.
 

If you have a matched source /line / termination a pulse waveform will be identical at both the transmitting and receiving ends. If the source/line/termination are not matched some of the power in the pulse will be reflected, causing pre-shoots and over shoots (pigs ears) on the pulse edges. For any given length of line these will be worse the sharper the rise and fall times of the pulse is.
Functionaltiy wise, they can often be seen on TV pictures, the added waveforms will give an echo effect and the left hand edge of bright object will be seen to have a black or white edge. They also cause digital communications to become unreliable, as a pre-shoot can be detected as an added digit.

Frank
 

If you are talking about digital switching logic it means the output impedance is different and one side is taking longer to recharge the attached capacitance/line. With short lines it is usaully not a problem, but in longer data transmission it does matter as Frank said. Slower rise an fall times could create in sychnrounous clocking system also unwanted jitter.

Enjoy your designwork!
 

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