Ultra low frequency VCO
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From: Tim Wescott on 5 Jul 2010 11:59 On 07/05/2010 12:01 AM, Daku wrote: > Could some electronics guru please help ? Is there any commonly > available reference design for an ultra low frequency voltage > controlled oscillator ? I developed a 60 Hz center frequency SPICE > model using common op-amps. I was wondering if there are any reference > designs out there. > Any feedback would be very useful. Thanks in advance for your help. I'd hardly call 60Hz "ultra low frequency". But it is pretty darned low. All the suggestions you've gotten so far are good as far as they go and may well be perfect -- but what are you trying to do? Do you need sine wave out or square? If sine wave, how pure? Do you have any specifications on jitter, phase noise, or frequency accuracy? You could digitally synthesize a 60Hz sine wave with a smallish processor -- I believe there are some TMS430 parts that could do it all in one package with a PWM output to be filtered by a simple RC. But "best" depends heavily on what you want. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
From: Sjouke Burry on 5 Jul 2010 17:23 Daku wrote: > Could some electronics guru please help ? Is there any commonly > available reference design for an ultra low frequency voltage > controlled oscillator ? I developed a 60 Hz center frequency SPICE > model using common op-amps. I was wondering if there are any reference > designs out there. > Any feedback would be very useful. Thanks in advance for your help. Buy a sine/cosine potentiometer, and put a motordrive on it with a reduction gear . Motor speed and gear will determine frequency, and supply voltage to the pot. will control amplitude. Or use a computerchip with ad channel to produce any signal you want. With a 16-24 bit audio ad chip it should work very well.
From: Paul Keinanen on 5 Jul 2010 18:01 On Mon, 05 Jul 2010 08:59:33 -0700, Tim Wescott <tim(a)seemywebsite.com> wrote: >On 07/05/2010 12:01 AM, Daku wrote: >> Could some electronics guru please help ? Is there any commonly >> available reference design for an ultra low frequency voltage >> controlled oscillator ? I developed a 60 Hz center frequency SPICE >> model using common op-amps. I was wondering if there are any reference >> designs out there. >> Any feedback would be very useful. Thanks in advance for your help. > >I'd hardly call 60Hz "ultra low frequency". But it is pretty darned low. At least for RF signals in free space according to ITU-R MF 300 kHz - 3 MHz LF 30 kHz - 300 kHz VLF 3 kHz - 30 kHz ULF 300 Hz - 3 kHz SLF 30 Hz - 300 Hz Thus 60 Hz would be Super Low Frequency. In different contexts ultra low frequency might refer to something with one cycle every second, hour or even weeks. > >All the suggestions you've gotten so far are good as far as they go and >may well be perfect -- but what are you trying to do? Do you need sine >wave out or square? If sine wave, how pure? Do you have any >specifications on jitter, phase noise, or frequency accuracy? > >You could digitally synthesize a 60Hz sine wave with a smallish >processor -- I believe there are some TMS430 parts that could do it all >in one package with a PWM output to be filtered by a simple RC. > >But "best" depends heavily on what you want. While very low frequencies could in principle be generated with traditional RLC components, the physical dimensions would become huge and in practice capacitor leakage resistance and coil series resistance would finally limit how low you could go. However, a digital circuit followed by a DAC could go as low as you want, however common audio DAC frequency response drops at about 3 Hz, limiting how low you can go with such components.
From: Tim Wescott on 5 Jul 2010 18:41 On 07/05/2010 03:01 PM, Paul Keinanen wrote: > On Mon, 05 Jul 2010 08:59:33 -0700, Tim Wescott<tim(a)seemywebsite.com> > wrote: > >> On 07/05/2010 12:01 AM, Daku wrote: >>> Could some electronics guru please help ? Is there any commonly >>> available reference design for an ultra low frequency voltage >>> controlled oscillator ? I developed a 60 Hz center frequency SPICE >>> model using common op-amps. I was wondering if there are any reference >>> designs out there. >>> Any feedback would be very useful. Thanks in advance for your help. >> >> I'd hardly call 60Hz "ultra low frequency". But it is pretty darned low. > > At least for RF signals in free space according to ITU-R > > MF 300 kHz - 3 MHz > LF 30 kHz - 300 kHz > VLF 3 kHz - 30 kHz > ULF 300 Hz - 3 kHz > SLF 30 Hz - 300 Hz > > Thus 60 Hz would be Super Low Frequency. > > In different contexts ultra low frequency might refer to something > with one cycle every second, hour or even weeks. From a "needs huge analog components to work" it's not ultra low to me -- but yes, from an RF standpoint it's below Ultra Low. >> All the suggestions you've gotten so far are good as far as they go and >> may well be perfect -- but what are you trying to do? Do you need sine >> wave out or square? If sine wave, how pure? Do you have any >> specifications on jitter, phase noise, or frequency accuracy? >> >> You could digitally synthesize a 60Hz sine wave with a smallish >> processor -- I believe there are some TMS430 parts that could do it all >> in one package with a PWM output to be filtered by a simple RC. >> >> But "best" depends heavily on what you want. > > While very low frequencies could in principle be generated with > traditional RLC components, the physical dimensions would become huge > and in practice capacitor leakage resistance and coil series > resistance would finally limit how low you could go. > > However, a digital circuit followed by a DAC could go as low as you > want, however common audio DAC frequency response drops at about 3 Hz, > limiting how low you can go with such components. I'd just use a general-purpose DAC for this, if I didn't PWM-and-filter. But, how far this needs to go depends on what the OP really needs, and he hasn't weighed in yet. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
From: Robert Baer on 5 Jul 2010 20:40
terryS wrote: > On Jul 5, 10:31 am, Spehro Pefhany <speffS...(a)interlogDOTyou.knowwhat> > wrote: >> On Mon, 5 Jul 2010 00:01:47 -0700 (PDT), the renowned Daku >> >> <dakup...(a)gmail.com> wrote: >>> Could some electronics guru please help ? Is there any commonly >>> available reference design for an ultra low frequency voltage >>> controlled oscillator ? I developed a 60 Hz center frequency SPICE >>> model using common op-amps. I was wondering if there are any reference >>> designs out there. >>> Any feedback would be very useful. Thanks in advance for your help. >> There's one on the LM324 datasheet that will be happy enough at 60Hz, >> plus it only uses 10-15 cents worth of parts. >> >> Best regards, >> Spehro Pefhany >> -- >> "it's the network..." "The Journey is the reward" >> sp...(a)interlog.com Info for manufacturers:http://www.trexon.com >> Embedded software/hardware/analog Info for designers: http://www.speff.com > > Unsophisticated and fixed one could use three components? > From a DC (or rectified AC) source of more tha 100 volts. > A resistor, a neon and a capacitor. > Size of capacitor determines rate. > I think it used to be called a 'Relaxation oscillator'? ....the reason for that name is: after it is made and connected, one can RELAX and see it OSCILLATE.. |