Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!apple!bionet!hayes.ims.alaska.edu!acad3.alaska.edu!ftpam1 From: ftpam1@acad3.alaska.edu (MUNTS PHILLIP A) Newsgroups: sci.electronics Subject: Re: Oscillators with extra-large frequency ranges Message-ID: <1991Jan6.025532.2642@ims.alaska.edu> Date: 6 Jan 91 02:55:32 GMT References: <6560003@hpfcbig.SDE.HP.COM> <44553@mips.mips.COM> Sender: usenet@ims.alaska.edu (J Random USENET) Reply-To: ftpam1@acad3.alaska.edu Organization: University of Alaska Fairbanks Lines: 46 News-Software: VAX/VMS VNEWS 1.3-4 Nntp-Posting-Host: acad3.alaska.edu 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