Low frequency analog VCO with sinewave output?

On Thu, 25 Aug 2011 08:23:49 +1000, Phil Allison wrote:

> "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.

You mean -- I made the error of thinking that there may be operational 
amplifiers out there that can drive more than 20mA?

Why, yes, Phil, I did.  But I didn't then, nor do I consider it now, an 
error.

>> C'mon Phil, make an assumption and run with it.
> 
> 
> ** Only autistic ratbags and total nut cases like YOU do stupid shit
> like that.

Look in the mirror, dude.

>     My god you are an utter, fucking  ASS.

Hmm.  Ears -- pink, hairless and short.  Tail -- nonexistent.  
Fingernails -- small.  Fingers & toes -- five to each extremity.

Nope, not an ass.  Sorry, you're wrong again.

-- 
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.

Take ATTiny13, make a predefined lookup table with pre-distorted 
sinewave, generate a noise chaped PWM. That would be absolutely the 
cheapest controllable and fairly accurate generator of a good quality 
sine wave.

Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

On Aug 25, 4:26=A0am, davew <david.wo...@gmail.com> wrote:
> On Aug 24, 6:57=A0pm, Tim Wescott <t...@seemywebsite.com> wrote:
>
>
>
> > On Wed, 24 Aug 2011 10:28:45 -0700, davew wrote:
> > > On Aug 24, 6:24=A0pm, Tim Wescott <t...@seemywebsite.com> wrote:
> > >> On Wed, 24 Aug 2011 05:15:09 -0700,BillSlomanwrote:
> > >> > On Aug 24, 7:22=A0pm, davew <david.wo...@gmail.com> 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.
>
> > >> > If you are restricted to one chip, this is probably as good as it
> > >> > gets. It distorts a triangular wave to a tolerable approximation t=
o a
> > >> > sine wave.
>
> > >> > You can do better by feeding a square wave through a shift registe=
r
> > >> > clock at some convenient multiple of the square wave frequency, ty=
ing
> > >> > a series of resistors to the outputs of the shift register and
> > >> > summing the currents through the resistors into a virtual earth to
> > >> > produce a staircase approximation to a sine wave, but it takes qui=
te
> > >> > a long shift register and quite a few close tolerance resistors to=
 do
> > >> > better than the 8038, and =A0it's still a three chip solution -
> > >> > basically a programmable logic device to provide the shift registe=
r
> > >> > and the dividers to generate the square wave, the VCO to to genera=
te
> > >> > the clock at some fairly high multiple of the output frequency, an=
d
> > >> > an op amp to sum the currents from the resistors, plus you have to
> > >> > find board space for the resistors.
>
> > >> > The Analog Devices DDS chips do provide a very good one chip solut=
ion
> > >> > - the more expensive chips include 14-bit DACs - but it isn't an
> > >> > analog solution.
>
> > >> How about a CD4040 and a bunch of resistors? =A0(I think I mean the
> > >> CD4040 -- the 4020, 4040, and 4060 are all big-ass counters, one of
> > >> which has an oscillator built in).
>
> > >> It's a ripple counter, but if you're going slow enough the clock
> > >> glitches shouldn't get you too bad.
>
> > >> --www.wescottdesign.com-Hidequoted text -
>
> > >> - Show quoted text -
>
> > > Thanks but I'm sticking with the analogue method in this case. Freque=
ncy
> > > stability isn't so much of a problem as I'm controlling frequency as
> > > part of a discrete PLL system.
>
> > A Wien-bridge oscillator with a couple of FETs for frequency control?
>
> > An SA602 with a crystal on the oscillator port and a really well filter=
ed
> > VCO oscillator on the antenna port? =A0With the right filtering that'd =
give
> > you a nice clean sine wave, and a frequency range from whatever you can
> > call "audio" right down through zero and out the other side. =A0The VCO
> > wouldn't need to be buffered -- the '602 doesn't _want_ much power on
> > it's antenna port, so you could just filter the snot out of the VCO
> > output and tap way down on the output tank circuit. =A0As long as you f=
eed
> > a sine wave in on one port or the other, and stay in the chips linear
> > range, you'll get really nice clean sine waves out.
>
> > --www.wescottdesign.com-Hide quoted text -
>
> > - Show quoted text -
>
> Interesting ideas. =A0From memory, doesn't the Wien-bridge oscillator
> need some form of amplitude stabilisation? =A0WIll look into that one.
> Re the SA602 - are yousaying this would provide a solution in itself
> with some external filtering? =A0Will investigate, thanks.

The Wien-bridge does need amplitude stabilisation; it can be as crude
as an incandescent filament in small light-bulb (think bicycle lamp)
but Jim Williams' various application notes about Wien Bridges for
Linear Technology mostly have a proper feed-back-controlled loop to
regulate the amplitude.

The Wien-bridge doesn't lend itself to variable frequencies, and I
don't think that I've ever seen it used in any kind of programmable
frequency generator. I'd be interested to hear how Tim Wescott
proposed to make the output frequency continuously adjustable.

--
Bill Sloman, Nijmegen

"davew" <david.wooff@gmail.com> wrote in message 
news:041fc111-2e28-4132-9126-c37d2f111910@18g2000yqu.googlegroups.com...
On Aug 24, 3:00 pm, dagmargoodb...@yahoo.com wrote:
> On Aug 24, 9:05 am, davew <david.wo...@gmail.com> wrote:
>
> Exar made the XR2206, trianglewave shaping method, THD 1-2%.
>
> --
> Cheers,
> James Arthur- Hide quoted text -
>
> - Show quoted text -

Great.  Thanks for all the ideas.  Looks like I need to compare the
8038 vs XR2206.
Dave W.

-----------------------------

I've tested both. On paper they seem similar, but in practice the XR2206 is 
clearly superior in temperature coefficient, linearity and noise immunity. 
Also easier to adjust for low distortion. I found no advantage to the 8038 
in my application. 

On Aug 25, 3:24=A0am, Tim Wescott <t...@seemywebsite.com> wrote:
> On Wed, 24 Aug 2011 05:15:09 -0700, Bill Sloman wrote:
> > On Aug 24, 7:22=A0pm, davew <david.wo...@gmail.com> 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.
>
> > If you are restricted to one chip, this is probably as good as it gets.
> > It distorts a triangular wave to a tolerable approximation to a sine
> > wave.
>
> > You can do better by feeding a square wave through a shift register
> > clock at some convenient multiple of the square wave frequency, tying a
> > series of resistors to the outputs of the shift register and summing th=
e
> > currents through the resistors into a virtual earth to produce a
> > staircase approximation to a sine wave, but it takes quite a long shift
> > register and quite a few close tolerance resistors to do better than th=
e
> > 8038, and =A0it's still a three chip solution - basically a programmabl=
e
> > logic device to provide the shift register and the dividers to generate
> > the square wave, the VCO to to generate the clock at some fairly high
> > multiple of the output frequency, and an op amp to sum the currents fro=
m
> > the resistors, plus you have to find board space for the resistors.
>
> > The Analog Devices DDS chips do provide a very good one chip solution -
> > the more expensive chips include 14-bit DACs - but it isn't an analog
> > solution.
>
> How about a CD4040 and a bunch of resistors? =A0(I think I mean the CD404=
0
> -- the 4020, 4040, and 4060 are all big-ass counters, one of which has an
> oscillator built in).
>
> It's a ripple counter, but if you're going slow enough the clock glitches
> shouldn't get you too bad.

Well, the CD4040 is cheap, but a progammable logic device can provide
the same funcion - and a lot more beside - in a single chip, which is
one of the things the OP is asking for.

And the CD4040 is slow - slow enough for it to be nuisance when I
first used the part back in 1975. It looks glacial these days.

--
Bill Sloman, Nijmegen

On Wed, 24 Aug 2011 18:20:51 -0700, Bill Sloman wrote:


> The Wien-bridge does need amplitude stabilisation; it can be as crude as
> an incandescent filament in small light-bulb (think bicycle lamp) but
> Jim Williams' various application notes about Wien Bridges for Linear
> Technology mostly have a proper feed-back-controlled loop to regulate
> the amplitude.
> 
> The Wien-bridge doesn't lend itself to variable frequencies, and I don't
> think that I've ever seen it used in any kind of programmable frequency
> generator. I'd be interested to hear how Tim Wescott proposed to make
> the output frequency continuously adjustable.
>

It's right there in my post.  What part of "use a JFET as an adjustable 
resistor" didn't you understand?

Note that it's not going to work for the OP: his desired frequency range 
is just too big.

-- 
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

On Wed, 24 Aug 2011 14:18:46 -0700 (PDT), davew
<david.wooff@gmail.com> 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.
>
>Many thanks to all.

Linear techology. AN13 page 12/13 

hth
-
Michael Wieser
-- 

On Aug 25, 6:49=A0pm, Michael Wieser <Mi_Wie...@web.de> wrote:
> On Wed, 24 Aug 2011 14:18:46 -0700 (PDT), davew
>
>
>
> <david.wo...@gmail.com> 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 cro=
ss
> >> 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 hav=
e
> >>> to be?
> >LF to MF audio band probably 70Hz - 3KHz
>
> >>> =A0 * How quiet does it need to be?
> >>> =A0 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.
>
> >>> =A0 * How linear does the command voltage vs. frequency need to be? *
> >I can only answer "nominally" linear. =A0Definitely 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. =A0I've not yet had enough
> >time to look at your other suggestions but will do. =A0I 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.
>
> Linear techology. AN13 page 12/13

An impressive circuit, through not a single chip solution. Sadly, it
depends on the Analog Devices AD639 which was one of Barry Gilbert's
more ingenious contributions to electronics - I would have loved to
have used it - but it's long obsolete.

http://www.datasheetcatalog.org/datasheet/analogdevices/AD639.pdf

--
Bill Sloman, Nijmegen

On Wed, 24 Aug 2011 18:20:51 -0700 (PDT), Bill Sloman
<bill.sloman@ieee.org> wrote:

>On Aug 25, 4:26&#4294967295;am, davew <david.wo...@gmail.com> wrote:
>> On Aug 24, 6:57&#4294967295;pm, Tim Wescott <t...@seemywebsite.com> wrote:
>>
>>
>>
>> > On Wed, 24 Aug 2011 10:28:45 -0700, davew wrote:
>> > > On Aug 24, 6:24&#4294967295;pm, Tim Wescott <t...@seemywebsite.com> wrote:
>> > >> On Wed, 24 Aug 2011 05:15:09 -0700,BillSlomanwrote:
>> > >> > On Aug 24, 7:22&#4294967295;pm, davew <david.wo...@gmail.com> 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.
>>
>> > >> > If you are restricted to one chip, this is probably as good as it
>> > >> > gets. It distorts a triangular wave to a tolerable approximation to a
>> > >> > sine wave.
>>
>> > >> > You can do better by feeding a square wave through a shift register
>> > >> > clock at some convenient multiple of the square wave frequency, tying
>> > >> > a series of resistors to the outputs of the shift register and
>> > >> > summing the currents through the resistors into a virtual earth to
>> > >> > produce a staircase approximation to a sine wave, but it takes quite
>> > >> > a long shift register and quite a few close tolerance resistors to do
>> > >> > better than the 8038, and &#4294967295;it's still a three chip solution -
>> > >> > basically a programmable logic device to provide the shift register
>> > >> > and the dividers to generate the square wave, the VCO to to generate
>> > >> > the clock at some fairly high multiple of the output frequency, and
>> > >> > an op amp to sum the currents from the resistors, plus you have to
>> > >> > find board space for the resistors.
>>
>> > >> > The Analog Devices DDS chips do provide a very good one chip solution
>> > >> > - the more expensive chips include 14-bit DACs - but it isn't an
>> > >> > analog solution.
>>
>> > >> How about a CD4040 and a bunch of resistors? &#4294967295;(I think I mean the
>> > >> CD4040 -- the 4020, 4040, and 4060 are all big-ass counters, one of
>> > >> which has an oscillator built in).
>>
>> > >> It's a ripple counter, but if you're going slow enough the clock
>> > >> glitches shouldn't get you too bad.
>>
>> > >> --www.wescottdesign.com-Hidequoted text -
>>
>> > >> - Show quoted text -
>>
>> > > Thanks but I'm sticking with the analogue method in this case. Frequency
>> > > stability isn't so much of a problem as I'm controlling frequency as
>> > > part of a discrete PLL system.
>>
>> > A Wien-bridge oscillator with a couple of FETs for frequency control?
>>
>> > An SA602 with a crystal on the oscillator port and a really well filtered
>> > VCO oscillator on the antenna port? &#4294967295;With the right filtering that'd give
>> > you a nice clean sine wave, and a frequency range from whatever you can
>> > call "audio" right down through zero and out the other side. &#4294967295;The VCO
>> > wouldn't need to be buffered -- the '602 doesn't _want_ much power on
>> > it's antenna port, so you could just filter the snot out of the VCO
>> > output and tap way down on the output tank circuit. &#4294967295;As long as you feed
>> > a sine wave in on one port or the other, and stay in the chips linear
>> > range, you'll get really nice clean sine waves out.
>>
>> > --www.wescottdesign.com-Hide quoted text -
>>
>> > - Show quoted text -
>>
>> Interesting ideas. &#4294967295;From memory, doesn't the Wien-bridge oscillator
>> need some form of amplitude stabilisation? &#4294967295;WIll look into that one.
>> Re the SA602 - are yousaying this would provide a solution in itself
>> with some external filtering? &#4294967295;Will investigate, thanks.
>
>The Wien-bridge does need amplitude stabilisation; it can be as crude
>as an incandescent filament in small light-bulb (think bicycle lamp)
>but Jim Williams' various application notes about Wien Bridges for
>Linear Technology mostly have a proper feed-back-controlled loop to
>regulate the amplitude.
>
>The Wien-bridge doesn't lend itself to variable frequencies,

Never heard of HP?

John

On Wednesday, August 24, 2011 10:29:49 PM UTC-7, Tim wrote:
> On Wed, 24 Aug 2011 18:20:51 -0700, Bill Sloman wrote:
> 
> > The Wien-bridge doesn't lend itself to variable frequencies, and I don't
> > think that I've ever seen it used in any kind of programmable frequency
> > generator. 

>  "use a JFET as an adjustable 
> resistor"

First problem: it'll take two adjustable elements, and they have to
change at the same time, in matched fashion.  That's  how
a Wein bridge works.   Matched jFET pairs are unobtainium.

Second problem: the voltage range for a jFET as variable resistance is
under a volt, and the usual bias assumes one of the terminals of the FET
is grounded.  The Wein bridge oscillator doesn't support that.

A possible workaround (if you can find 'em) is to use photoresistors, 
in a matched-pair illuminated by a common light source.