[time-nuts] T.I. questions (Magnus Danielson)

johncroos johncroos at aol.com
Sat Feb 7 14:37:18 EST 2015


A further comment on design of pseudo random code
generators. At some point the code may enter the dreaded all
"zeros" state. This clocks a zero on the input stage through all stages
and the whole thing just stops. So a AND gate looking
at all stages in parallel is used
to  detect the all zero state and get things going again. 
One way is to XOR the output of the AND and the input to any stage.
since the all zero state is not permitted the length of the code is can
be no longer than the well known 2^n -1 bits.

Also if the number of codes desired is limited - some of the FFs
may be replace by a delay line. Using MECL III and a delay line
a 350 MHz rather long code generator was implemented in my lab
with only few JK FFs. That was in about 1979. For more info
see Dixon "Spread Spectrum Systems".   john roos k6iql


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