🚀 go-pugleaf

In article <44553@mips.mips.COM>, mark@mips.COM (Mark G. Johnson) writes...
> 
>   >> As a hobbyist electronician I have come across a real problem.
>   >> For a certain project, I would need an oscillator with digital,
>   >> LOGARITHMIC adjusting (32-bit, 1000 x log) and a HUGE range,
>   >> 1 kHz to 100 MHz. Is this at all possible?
> 
>In <6560003@hpfcbig.SDE.HP.COM> bame@hpfcbig.SDE.HP.COM (Paul Bame) writes:
>  >The incredibly precise logarithmic control may be a real pain - just
>  >consider the problem of accurately measuring 1 (log) bit in 32 bits with a
>  >frequency counter - you might need an expensive counter with a very long
>  >capture time to resolve 1KHz from 1KHz + 1 bit.  You didn't mention how fast
>  >this thing is required to change frequency.
> 
> 
> 
>Just to consider it from another angle .... 32-bit frequency control requires
>what kind of resolution in _TIME_??  There are 2^32 = 4294967296 different
>frequencies.  If let "R" stand for the ratio between frequencies, then
> 
>   1kHz * (R ^ 4294967296) = 100 MHz,  hence R = 1.00000000321667422079114998.
> 
>The uppermost frequency is 100.0000000MHz ; the next lower frequency
>is (100MHz / R) = 99.999999678332578955584303 MHz.  The _periods_ of the
>waveforms are:
> 
> 100.000000000000000000000000 MHz:  period = 10000000.00000000000 femtoseconds
>  99.999999678332578955584303 MHz:  period = 10000000.03216674221 femtoseconds
> 
>This would be exceedingly difficult to do, and even more difficult to
>verify / validate / certify.  For example the timebase must have an
>accuracy of better than one part in 4294967296, while quartz crystals
>are typically 10 ppm (43000 parts in 4294967296).
>-- 
> -- Mark Johnson	
> 	MIPS Computer Systems, 930 E. Arques M/S 2-02, Sunnyvale, CA 94086
>	(408) 524-8308    mark@mips.com  {or ...!decwrl!mips!mark}

     The design could be easily (albeit expensively) done with one of the new
direct digital synthesizers.  For example, Stanford Telecom (408-980-5684) has
a board in their catalog that does 0-110 MHz with 28 bits of frequency
resolution.  It costs $1750.  With a 300 MHz clock, 28 bits yields 1.1 Hz steps.

Philip Munts N7AHL
NRA Extremist, etc.
University of Alaska, Fairbanks