Groups > sci.electronics.design > #452188

Re: Low Frequency 3rd Overtone Crystal Osc

From	rickman <gnuarm@gmail.com>
Newsgroups	sci.electronics.design
Subject	Re: Low Frequency 3rd Overtone Crystal Osc
Date	2017-03-16 19:14 -0400
Organization	A noiseless patient Spider
Message-ID	<oaf63t$7vn$1@dont-email.me> (permalink)
References	(9 earlier) <65bkccttgadbrtf4j9ojv7s5lbjp19oecv@4ax.com> <oadcgn$sqo$2@dont-email.me> <fuekcct0911kumd3v1hmlek5kuvttvp6qa@4ax.com> <oaditf$esk$1@dont-email.me> <303mcctas9ekomsgmd5q92ui9gib7d81l2@4ax.com>

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On 3/16/2017 6:22 PM, upsidedown@downunder.com wrote:
> On Thu, 16 Mar 2017 04:40:52 -0400, rickman <gnuarm@gmail.com> wrote:
>
>> On 3/16/2017 3:28 AM, upsidedown@downunder.com wrote:
>>> On Thu, 16 Mar 2017 02:51:41 -0400, rickman <gnuarm@gmail.com> wrote:
>>>
>>>> On 3/16/2017 2:20 AM, upsidedown@downunder.com wrote:
>>>>> On Wed, 15 Mar 2017 12:44:10 -0400, rickman <gnuarm@gmail.com> wrote:
>>>>>
>>>>>>>
>>>>>>>
>>>>>>> This may be a heresy:
>>>>>>>
>>>>>>> There are plenty of small ARM Cortex-M chips with built-in
>>>>>>> counter-timers. Get one of them with a decent crystal (say in the range of
>>>>>>> 5 to 20 MHz) and divide from it with the built-in timer. The cost
>>>>>>> will be just some dollars for the components.
>>>>>>>
>>>>>>> A small Cortex evaluation unit can be had for some tens of dollars,
>>>>>>> and there are the crystal and board built-in, together with some
>>>>>>> means of getting the code in.
>>>>>>
>>>>>> Thanks for the suggestion, but that does not fit the problem space.  The
>>>>>> FPGA board I am prototyping with has an oscillator on board, just not a
>>>>>> multiple of 240 kHz.  This is a very low power design and every ARM type
>>>>>> CPU I have seen will consume mAs of current with the high speed crystal
>>>>>> controlled clock.
>>>>>
>>>>> How about a free running CPU clock running at a few MHz and a crystal
>>>>> in 0.5 to 1.5 MHz range generating an interrupt about every
>>>>> microsecond. The interrupt updates the NCO (numerical controlled
>>>>> oscillator) 16 to 32 bit phase accumulator and some bits are written
>>>>> to the output pins. The rest of the time, the processor is kept in  a
>>>>> low power sleep mode. If sin/cos output is needed, insert a sine
>>>>> lookup table between the phase accumulator and output pins.
>>>>> These should not require many instructions, so the power consumption
>>>>> should be low.
>>>>
>>>> I appreciate the suggestion, but why all the complexity?  If I have a
>>>> crystal creating a clock, I don't need the CPU.  What you described is
>>>> way more power and complexity than needed.
>>>
>>> I understood that you originally had problems ordering a crystal for
>>> the exact integer multiple of 120 kHz. The NCO principle allows you to
>>> generate any frequency from an other frequency, which doesn't have to
>>> be harmonically related, as long as the Nyquist criterion is followed.
>>
>> That's not entirely correct.  To get an exact value the reference
>> frequency and the target frequency must be related by the ratio of two
>> integers.  Fclk = Fref * NCOstep / NCOmodulus where NCOstep is the phase
>> increment and NCOmodulus is the modulus of the phase accumulator.
>
> Increasing the phase accumulator width is usually cheap. Most people
> think about 16/24 bit phase accumulators. I have used 64 bit
> accumulators in some time keeping applications. Of course, this is
> ultimately limited by the accuracy of the frequency source.
>
> When doing the NCO in software using longer phase accumulators than
> the machine word, one has to be careful how the phase accumulator
> value is copied to the outside world from the ISR (interrupt service
> routine). Copying only the most significant machine word should be OK
> and let the ISR also increment locally the "invisible" low part of the
> phase accumulator should do the trick.

Discarding (or rounding, same thing) part of the phase word before 
converting to a sine wave introduces a jitter which shows up as spurs 
close to the fundamental and so can not be easily filtered.  Phase 
truncation creates real problems for many apps.

-- 

Rick C

Thread

Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-08 17:51 -0500
  Re: Low Frequency 3rd Overtone Crystal Osc Jon Elson <jmelson@wustl.edu> - 2017-03-08 17:04 -0600
    Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-08 19:57 -0500
    Re: Low Frequency 3rd Overtone Crystal Osc Robert Baer <robertbaer@localnet.com> - 2017-03-10 00:01 -0800
  Re: Low Frequency 3rd Overtone Crystal Osc dagmargoodboat@yahoo.com - 2017-03-08 18:02 -0800
    Re: Low Frequency 3rd Overtone Crystal Osc John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-03-08 18:13 -0800
      Re: Low Frequency 3rd Overtone Crystal Osc Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-03-09 09:11 -0500
        Re: Low Frequency 3rd Overtone Crystal Osc John Larkin <jjlarkin@highlandtechnology.com> - 2017-03-09 08:14 -0800
          Re: Low Frequency 3rd Overtone Crystal Osc Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-03-09 11:24 -0500
          Re: Low Frequency 3rd Overtone Crystal Osc bitrex <bitrex@de.lete.earthlink.net> - 2017-03-11 11:20 -0500
      Re: Low Frequency 3rd Overtone Crystal Osc Neon John <no@never.com> - 2017-03-09 16:24 -0500
        Re: Low Frequency 3rd Overtone Crystal Osc John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-03-09 14:23 -0800
          Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-09 18:16 -0500
          Re: Low Frequency 3rd Overtone Crystal Osc Neon John <no@never.com> - 2017-03-13 19:59 -0400
            Re: Low Frequency 3rd Overtone Crystal Osc John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-03-13 17:29 -0700
              Re: Low Frequency 3rd Overtone Crystal Osc bill.sloman@ieee.org - 2017-03-13 18:43 -0700
            Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-13 21:54 -0400
      Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-10 10:15 +0000
    Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-08 22:33 -0500
      Re: Low Frequency 3rd Overtone Crystal Osc o pere o <me@somewhere.net> - 2017-03-09 15:39 +0100
      Re: Low Frequency 3rd Overtone Crystal Osc bitrex <bitrex@de.lete.earthlink.net> - 2017-03-09 09:41 -0500
        Re: Low Frequency 3rd Overtone Crystal Osc bitrex <bitrex@de.lete.earthlink.net> - 2017-03-09 09:43 -0500
          Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-09 11:17 -0500
            Re: Low Frequency 3rd Overtone Crystal Osc bitrex <bitrex@de.lete.earthlink.net> - 2017-03-09 20:42 -0500
              Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-09 20:55 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc piglet <erichpwagner@hotmail.com> - 2017-03-11 07:37 +0000
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-11 03:15 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc piglet <erichpwagner@hotmail.com> - 2017-03-11 09:52 +0000
                Re: Low Frequency 3rd Overtone Crystal Osc bitrex <bitrex@de.lete.earthlink.net> - 2017-03-11 08:54 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc bitrex <bitrex@de.lete.earthlink.net> - 2017-03-11 09:00 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc Jasen Betts <jasen@xnet.co.nz> - 2017-03-11 23:58 +0000
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-11 22:13 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-03-13 11:20 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-13 11:47 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-13 23:44 +0200
                Re: Low Frequency 3rd Overtone Crystal Osc Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-03-13 15:55 -0700
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-13 19:58 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc Jasen Betts <jasen@xnet.co.nz> - 2017-03-14 04:48 +0000
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-14 13:37 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2017-03-14 22:29 +0200
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-14 20:59 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2017-03-15 10:40 +0200
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-15 12:44 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-16 08:20 +0200
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-16 02:51 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-16 09:28 +0200
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-16 04:40 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc bill.sloman@ieee.org - 2017-03-16 05:09 -0700
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-16 12:47 -0400
                Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-17 00:22 +0200
                Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-16 19:14 -0400
    Re: Low Frequency 3rd Overtone Crystal Osc John S <Sophi.2@invalid.org> - 2017-03-13 05:51 -0500
      Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-13 08:39 -0400
  Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-09 21:09 -0500
  Re: Low Frequency 3rd Overtone Crystal Osc "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-09 20:15 -0600
    Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-09 23:36 -0500
      Re: Low Frequency 3rd Overtone Crystal Osc "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-10 19:02 -0600
        Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-11 01:15 -0500
          Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-11 11:04 +0200
          Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-11 09:31 +0000
      Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-11 09:15 +0000
        Re: Low Frequency 3rd Overtone Crystal Osc bitrex <bitrex@de.lete.earthlink.net> - 2017-03-11 10:50 -0500
          Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-11 16:46 +0000
        Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-11 15:36 -0500
          Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-11 23:50 +0000
            Re: Low Frequency 3rd Overtone Crystal Osc "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-11 17:59 -0600
              Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-12 08:44 +0000
                Re: Low Frequency 3rd Overtone Crystal Osc "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-12 20:23 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-13 12:21 +0000
                Re: Low Frequency 3rd Overtone Crystal Osc "Tim Williams" <tiwill@seventransistorlabs.com> - 2017-03-14 03:30 -0500
                Re: Low Frequency 3rd Overtone Crystal Osc "Kevin Aylward" <kevinRemovAT@kevinaylward.co.uk> - 2017-03-14 20:50 +0000
  Re: Low Frequency 3rd Overtone Crystal Osc Robert Baer <robertbaer@localnet.com> - 2017-03-09 23:57 -0800
    Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-10 05:51 -0500
    Re: Low Frequency 3rd Overtone Crystal Osc Mike Jones <mikejones@gmail.com> - 2017-03-10 06:03 -0600
  Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-10 15:34 +0200
  Re: Low Frequency 3rd Overtone Crystal Osc Tim Wescott <tim@seemywebsite.really> - 2017-03-11 12:51 -0600
    Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-12 00:33 +0200
      Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-12 01:00 -0500
        Re: Low Frequency 3rd Overtone Crystal Osc upsidedown@downunder.com - 2017-03-12 10:45 +0200
          Re: Low Frequency 3rd Overtone Crystal Osc rickman <gnuarm@gmail.com> - 2017-03-12 18:32 -0400
    Re: Low Frequency 3rd Overtone Crystal Osc Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-03-13 11:26 -0400

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