Hi A lot depends on weather this is a one off basement project or a commercial endeavor. If it's commercial, there are people who will sell you a packaged part that will do the 10 MHz to T1 conversion.
Bob On Jul 4, 2010, at 10:38 PM, Hal Murray wrote: > >> I would like to generate a DS-1 timing reference from 10 MHz, e.g a >> T-bolt. Thought someone here might be able to suggest a starting point. > > One approach is a PLL. You will have to divide 1.544 MHz by 193 and 10 MHz > by 1250. If you want to use the TAPR Clock-Block, I think you will need > something like a divide by 10 between the 10 MHz and the Clock-Block to get > the numbers within range. > > I wonder if you could use a VCXO and fit all the logic in a tiny micro. It > would probably need a few external parts to filter the PWM output. Maybe the > filtering inside the VCXO would be good enough. > > > Another approach is to use a DDS. Analog Devices makes the whole thing in > one package, but the numbers don't work out exactly. How close to you need > to be? With a 32 bit (binary) adder, you get 1544000.001158 MHz. With 48 > bits you get 1543999.999999989825. > > But you don't have to use a binary adder. You have 10000000 Hz and you want > 1544000 Hz, so you need to multiply by 1544000 and divide by 10000000. That > reduces to 193 / 1250. So add 193 each cycle using modulo 1250 addition. > Each time it overflows, kick out a pulse. If you want a square wave output, > divide by 625 and toggle the output on each overflow. That sort of logic > fits well in a FPGA/CPLD. > > That will give you a clock that's locked to your input clock but with lots of > jitter. (up to 1/2 clock off in each direction, so 100 ns peak-to-peak) > > You can run that through a low pass filter and/or feed the top bits into a > sine table and on to a DAC. Note that isn't the standard ROM. You have to > make a new table for each modulus and if you are using standard ROMs with > binary addressing you will waste up to 1/2 of each ROM. > > -- > These are my opinions, not necessarily my employer's. I hate spam. > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
