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EMC frequencies.. beginners questions about rise time

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ku637

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Hi,

I'm trying to understand the EMC problems that can arise from digital circuits.

I've one board where there is an SRAM part number IS61WV25616BLL-10BLI operating at 3.3V (datasheet attached)
It is specified as 8ns speed (read cycle time) and 1V/ns rise time.

Can we correlate this information to the potential EMC frequencies that can arise from this circuit?or How to estimate the potential problematic frequencies with this information..

I ve read that as the rise time decreases the band width of the system increases and the relation tr=0.35/f

Here should i calculate using a continuous read cycle of 8ns or just use the rise time (since operating voltage is 3.3V im assuming it like 3.3ns , as 1V/ns is mentioned) ?

Thanks for any help.
 

The risetime give you the ultimate bandwidth of the signal, its repetition rate give you the sideband distribution within that spectrum. So a 1KHZ square wave with a nS rise time would give you a comb of frequencies at 1KHZ difference right into the GHZ, but each individual harmonic would be a a very low amplitude(1/n). A 20 MHz square wave with a 8nS rise time would give you multiples of 20 MHZ.
So its the clock (or R/W pulses) multiples that will cause you grief up to the b/w limitation set by the rise time.
Frank
 

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