1/19/2008
Copyright
2005 – Tim Hoerning
27
Errors & Error Correction
•The read state of a digital signal is determined by a threshold
–Above the threshold and the value is read as a 1
–Below the threshold and the value is read as a 0
–Once a bit is read incorrectly, it cannot be corrected
unless error correction
is used
–Actual digital devices usually don’t use a simple
threshold. Instead they have a valid 1 region and a valid 0 region
with a “dead zone” between
them.
•Error Correction
–Used on some common formats such as CDs
–Adds overhead.
Required storage can be more than 2x that required to store data unprotected
–Still has it’s limits.
Nothing can correct all errors.