Low frequency analog VCO with sinewave output?

On a sunny day (Wed, 24 Aug 2011 20:19:01 +0200) it happened Sjouke Burry
<burrynulnulfour@ppllaanneett.nnll> wrote in
<4e5540ef$0$3722$703f8584@textnews.kpn.nl>:

>Jan Panteltje wrote:
>> On a sunny day (Wed, 24 Aug 2011 02:22:29 -0700 (PDT)) it happened davew
>> <david.wooff@gmail.com> wrote in
>> <aff45f3b-ff96-4d35-b3e0-d53ed85225dc@d25g2000yqh.googlegroups.com>:
>> 
>>> I'm searching for a simple one chip solution if anyone has any ideas.
>>> Best I've found so far might be the old 8038 function generator chip.
>> 
>> There was this 22?? sort of chip that does triangle and sine.
>> Used, it, if I only could remember the number...
>> :-)
>> 
>I remember them. Lousy quality, the sine was approximated with a diode
>cicuit, which left visible artifacts.

Was OK for a simple modem though.

On Wed, 24 Aug 2011 11:20:54 -0700, davew wrote:

> On Aug 24, 6:31&nbsp;pm, Tim Wescott <t...@seemywebsite.com> wrote:
>> On Wed, 24 Aug 2011 02:22:29 -0700, davew wrote:
>> > I'm searching for a simple one chip solution if anyone has any ideas.
>> > Best I've found so far might be the old 8038 function generator chip.
>>
>> A PIC with a PWM output, a resistor, a cap, and a blindfold.
>>
>> The blindfold is to make it "analog".
>>
>> But why do you need it to be analog? &nbsp;In particular, if the 8038 is
>> good enough, why can't a _really cruddy_ digital solution work just
>> fine? Those old "triangle into sine" generators had really nasty
>> glitches at the peaks of the sine waves, and I'm not even going to
>> guess at the overall harmonic distortion (or temperature dependence
>> thereof).
>>
>> Which leads to the questions:
>>
>> * What frequency range does it need to run in? * How good does it have
>> to be?
>> &nbsp; * How quiet does it need to be?
>> &nbsp; * How linear does the command voltage vs. frequency need to be? *
>> &nbsp; How close to a sine does it need to be?
>> * Temperature range?
>> * what other questions did I leave out?
>>
>> --www.wescottdesign.com
> 
> I do appreciate what you are saying and don't disagree but in this
> application I want to do some good old fashioned mucky analogue signal
> processing, not PIC programming (even if I had any PIC experience).

If you used a 555 followed by an active filter with a sharp cutoff, you 
could get a pretty nice sine wave in a narrow band of frequencies.  Since 
you haven't answered my questions about your needs, I can only say that 
it'll work great.

There's a bazillion ways to do this to meet your stated requirements -- 
but only because your stated requirements are _very very broad_.

-- 
www.wescottdesign.com

On 24/08/2011 10:11 PM, Phil Allison wrote:
>> "dave the fuckwit wanker"
>>
>> ** FFS - define " low frequency "'
>>
>> We are not fucking mind readers !!!!!!!!!
>>
>> You stupid POS.
>>
>
> Well you should have ...
>
>
> ** You should have been aborted.
>
>
> Audio band is what I'm interested in.
>
>
> ** Now you tell us.
>
>    You stupid, bullshitting PITA cunthead
>
>    FOAD
>
>
>
> .... Phil
>
>

That is enough, Phil. If you won't treat people with any respect, why 
should I treat you with any.

On Wednesday, August 24, 2011 2:22:29 AM UTC-7, davew wrote:
> I'm searching for a simple one chip solution if anyone has any ideas.
> Best I've found so far might be the old 8038 function generator chip.

[for a sinewave VCO to be phase-locked]

The sad truth is that square-triangle wave generators are easy to
voltage control, and most voltage-controlled options for sinewaves
are crufty filtering/shaping addons to the square-triangle generator.
An alternative that I particularly like uses programmable impedance
amps for a phase-shift oscillator, i.e. figure 17 in

<http://www.national.com/pf/LM/LM13700.html>

It uses two chips, but they're under a buck.   This needs a matched
trio of timing capacitors, so is gonna get complicated if you need
multiple-range switching.

> If you cough up answers to my questions on what you really need, folks
> will be able to give you more specific help.
>
> I understand not wanting to break the digital barrier -- I tend to cross
> that particular Rubicon with ease, yet I have circuits out there that are
> all analog, or that only use "digital" parts in an analog way.

I'm deliberately trying to make an all analogue design in this case so
it's not that I'm particularly averse to taking a digital approach as
such.

>> * What frequency range does it need to run in? * How good does it have
>> to be?
LF to MF audio band probably 70Hz - 3KHz

>>   * How quiet does it need to be?
>>   How close to a sine does it need to be?
Not sure really, I would have thought 2% THD+N would be good enough
but I find it difficult to be accurate without having performed any
experimentation yet.

>>   * How linear does the command voltage vs. frequency need to be? *
I can only answer "nominally" linear.  Definitely not log.

>> * Temperature range?
10 - 30 degC

>> * what other questions did I leave out?
Well I suppose the amplitude needs to be reasonably stable with
frequency but again only to within say 10%.

I think the XR2206 looks promising so far.  I've not yet had enough
time to look at your other suggestions but will do.  I particularly
like the idea of a Wien-bridge if it's easy enough to tune because
there is no digital switching going on internally, so should be
inherently more quiet.

Many thanks to all.

On Wed, 24 Aug 2011 14:18:46 -0700, davew wrote:

>> If you cough up answers to my questions on what you really need, folks
>> will be able to give you more specific help.
>>
>> I understand not wanting to break the digital barrier -- I tend to
>> cross that particular Rubicon with ease, yet I have circuits out there
>> that are all analog, or that only use "digital" parts in an analog way.
> 
> I'm deliberately trying to make an all analogue design in this case so
> it's not that I'm particularly averse to taking a digital approach as
> such.
> 
>>> * What frequency range does it need to run in? * How good does it have
>>> to be?
> LF to MF audio band probably 70Hz - 3KHz
> 
>>>   * How quiet does it need to be?
>>>   How close to a sine does it need to be?
> Not sure really, I would have thought 2% THD+N would be good enough but
> I find it difficult to be accurate without having performed any
> experimentation yet.
> 
>>>   * How linear does the command voltage vs. frequency need to be? *
> I can only answer "nominally" linear.  Definitely not log.
> 
>>> * Temperature range?
> 10 - 30 degC
> 
>>> * what other questions did I leave out?
> Well I suppose the amplitude needs to be reasonably stable with
> frequency but again only to within say 10%.
> 
> I think the XR2206 looks promising so far.  I've not yet had enough time
> to look at your other suggestions but will do.  I particularly like the
> idea of a Wien-bridge if it's easy enough to tune because there is no
> digital switching going on internally, so should be inherently more
> quiet.

You are going to find that tuning range to be challenging, both because 
70Hz is going to require large capacitances, high circuit impedances, or 
both, and because you're trying to make the thing work over a 43:1 range.

My Wien bridge idea is _not_ going to work without switched 
capacitances.  In fact, my suggestion for a SA612 with one crystal and 
one LC oscillator isn't a good one, either -- even a 1MHz LC oscillator 
is going to want to have more than a 3000kHz range.

If someone were holding a gun to my head to do this with analog circuits, 
I'd do the SA612 solution with two matched crystals with resonant 
frequencies in the single-digit MHz region.  I'd "rubber" one crystal by 
putting it in series with a varicap diode, and I'd sweat bullets to make 
sure that I could get down to a 70Hz difference in frequencies without 
either crossing my frequencies over (which would get me an audio tone 
with the voltage to frequency gain reversed) or having some instances of 
the circuit fail to get down to 70Hz in production.

If a customer asked me to do it, even if they jumped up and down and 
turned red in the face every time I said "digital", I'd give them one 
estimate for the analog way, and a second, significantly lower one, for 
the digital way.

Having tried to rain on your parade _again_, I will say that I think the 
mixer/RF oscillator approach should work pretty well, and without a whole 
lot of components.

-- 
www.wescottdesign.com

davew wrote:
> I'm searching for a simple one chip solution if anyone has any ideas.
> Best I've found so far might be the old 8038 function generator chip.

How load and how clean?

Wien Bridge comes to mind for low frequency..


Jamie

"Tim Wescott = a Fucking Liar"


> This from Phil "All conceivable operational amplifiers can drive only
> 20mA" Allison.

**  That is a fucking absurd lie.

   YOU made that error   -  not me.



> C'mon Phil, make an assumption and run with it.


** Only autistic ratbags and total nut cases like YOU do stupid shit like 
that.

    My god you are an utter, fucking  ASS.



...  Phil

"Tim Wescott = Total Fucking Liar "


> If you cough up answers to my questions on what you really need, folks
> will be able to give you more specific help.
>

** You don't say .............

 What a fucking hypocrite.



.... Phil 

davew"


**  Fuck off Google monkey.