Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!mips!hal!mark From: mark@mips.COM (Mark G. Johnson) Newsgroups: sci.electronics Subject: Re: Oscillators with extra-large frequency ranges Message-ID: <44553@mips.mips.COM> Date: 5 Jan 91 23:54:13 GMT References: <6560003@hpfcbig.SDE.HP.COM> Sender: news@mips.COM Reply-To: mark@mips.COM (Mark G. Johnson) Organization: MIPS Computer Systems, Inc. Lines: 36 >> 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}