Low frequency analog VCO with sinewave output?

On Thu, 25 Aug 2011 11:43:12 -0700, whit3rd wrote:

> 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.

It was kind of an off the cuff suggestion.  You could make a state-space 
oscillator, i.e. two op-amp integrators one after the other, each with a 
JFET-based attenuator.  That'd give you the same effect as a Wien bridge, 
and the only thing that mismatch would do would be to make the amplitudes 
of the two stages mismatched.

I don't think you'd get close to the OP's desired 50:1 frequency ratio 
with JFETs, though, and any wholly analog solution would be challenging.

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

True.  I'm not sure how important an exact match is -- a Wien bridge will 
probably still oscillate just fine with mismatched resistors, just with 
the states imbalanced somewhat.  How would they be imbalanced -- I 
dunno.  That's an exercise for the reader.

-- 
www.wescottdesign.com

On Wed, 24 Aug 2011 21:53:24 -0700, Bill Sloman wrote:

> On Aug 25, 3:24&nbsp;am, Tim Wescott <t...@seemywebsite.com> wrote:
>> On Wed, 24 Aug 2011 05:15:09 -0700, Bill Sloman wrote:
>> > On Aug 24, 7:22&nbsp;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 &nbsp;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? &nbsp;(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.
> 
> 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.

At one point you could get 74HC4040 parts -- dunno if they're still out 
there.

I was thinking of that part because of the built-in oscillator -- what 
programmable logic part has that?

-- 
www.wescottdesign.com

On Wed, 24 Aug 2011 17:57:06 -0500, Vladimir Vassilevsky wrote:

> 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.

Curiosity (well, sloth): does it have an on-board ADC?

This is basically what I suggested (except I suggested a PIC).  The OP 
wants analog only, for whatever reason.

-- 
www.wescottdesign.com

On Wed, 24 Aug 2011 23:01:23 +1000, "Phil Allison" <phil_a@tpg.com.au>
wrote:

>
>"John Fields
> "Phil Allison"
>>
>>>"dave wanker"
>>>
>>>
>>>** FFS  -  define " low frequency "'
>>
>> Clue:
>>
>> "Best I've found so far might be the old 8038 function generator
>> chip."
>>
>
>**  WTF is your problem  -   shit head ???
>
>The 8083 operates from  0.001 Hz  to  300kHz.
>
>Which bit of that   FUCKING  ENORMOUS  range is automatically
>
> " low frequency "  ??????????    eh  ???
>
>You context blind,  ASD fucked, septic bloody moron.

---
Geez, Phil, when you pissue epithets like that it makes it difficult
for other than civilized players to reply to your feigned vitriol if
they have no emollient at hand.

Is that what you want?

I have great respect for you and your point is taken.

Mine was that, since the 8038 the OP considered as a baseline
candidate for his needs goes from wherever to wherever, another chip
sporting the same, or greater f(v) would work; the challenge being to
find that chip.

-- 
JF

"John Fields"
>>
>>"John Fields
>> "Phil Allison"
>>>
>>>>"dave wanker"
>>>>
>>>>
>>>>** FFS  -  define " low frequency "'
>>>
>>> Clue:
>>>
>>> "Best I've found so far might be the old 8038 function generator
>>> chip."
>>>
>>
>>**  WTF is your problem  -   shit head ???
>>
>>The 8083 operates from  0.001 Hz  to  300kHz.
>>
>>Which bit of that   FUCKING  ENORMOUS  range is automatically
>>
>> " low frequency "  ??????????    eh  ???
>>
>>You context blind,  ASD fucked, septic bloody moron.
>
> ---
> Geez, Phil, when you pissue epithets like that it makes it difficult
> for other than civilized players to reply to your feigned vitriol if
> they have no emollient at hand.
>
> Is that what you want?


**  Fuck off.

> I have great respect for you and your point is taken.
>
> Mine was that, since the 8038 the OP considered as a baseline
> candidate for his needs goes from wherever to wherever, another chip
> sporting the same, or greater f(v) would work; the challenge being to
> find that chip.


** You posted nothing of the kind.

    Piss off.


....  Phil

On Aug 25, 3:29=A0pm, Tim <t...@seemywebsite.please> wrote:
> On Wed, 24 Aug 2011 18:20:51 -0700, Bill Sloman wrote:
> > The Wien-bridge does need amplitude stabilisation; it can be as crude a=
s
> > 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. =A0What part of "use a JFET as an adjustable
> resistor" didn't you understand?

You'd need more than "a JFET" to make the frequency adjustable over
any singificant range. Most Wien bridges use a JFET as an adjustable
resistor to control the amplitude, so it wasn't exactly obvious that
your single JFET was intended to adjust the frequency.

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

Quite a part from the fact that it would be hard to make it work well
for other reasons.

--
Bill Sloman, Nijmegen

On Aug 26, 3:06=A0am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Wed, 24 Aug 2011 18:20:51 -0700 (PDT),BillSloman
>
>
>
> <bill.slo...@ieee.org> wrote:
> >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 approximatio=
n to a
> >> > >> > sine wave.
>
> >> > >> > You can do better by feeding a square wave through a shift regi=
ster
> >> > >> > 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 =A0it's still a three chip solution -
> >> > >> > basically a programmable logic device to provide the shift regi=
ster
> >> > >> > and the dividers to generate the square wave, the VCO to to gen=
erate
> >> > >> > 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 so=
lution
> >> > >> > - the more expensive chips include 14-bit DACs - but it isn't a=
n
> >> > >> > analog solution.
>
> >> > >> How about a CD4040 and a bunch of resistors? =A0(I think I mean t=
he
> >> > >> 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-Hidequotedtext -
>
> >> > >> - Show quoted text -
>
> >> > > Thanks but I'm sticking with the analogue method in this case. Fre=
quency
> >> > > 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 fil=
tered
> >> > 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 o=
n
> >> > 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 yo=
u feed
> >> > a sine wave in on one port or the other, and stay in the chips linea=
r
> >> > range, you'll get really nice clean sine waves out.
>
> >> > --www.wescottdesign.com-Hidequoted 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,
>
> Never heard of HP?

Sorry about that. But the OP was asking for a voltage-controlled
oscillator. I admit that if you stuck a DC motor on the front of an
HP200 you could make it act as a voltage-controller oscillator, but
this is a long way from the single-chip soluution that the OP was
asking for

http://www.ohio.edu/people/postr/bapix/HP200CD.htm

http://www.ohio.edu/people/postr/bapix/HP200CD.htm

From the pictures it looks as if the fine control of frequency
depended on a pair of rotating segment variable capacitors, which
isn't an approach that anybody seems to have duplicated inside a
single chip.

--
Bill Sloman, Nijmegen

On Aug 26, 5:26=A0am, Tim Wescott <t...@seemywebsite.com> wrote:
> On Wed, 24 Aug 2011 21:53:24 -0700,BillSlomanwrote:
> > On Aug 25, 3:24=A0am, 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 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, tyin=
g
> >> > 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 d=
o
> >> > better than the 8038, and =A0it'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 solutio=
n
> >> > - 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.
>
> > 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.
>
> At one point you could get 74HC4040 parts -- dunno if they're still out
> there.
>
> I was thinking of that part because of the built-in oscillator -- what
> programmable logic part has that?

http://www.datasheetcatalog.org/datasheet/philips/74HC4040.pdf

Some of the biggish CMOS counters RCA made at that time had built-in
oscillator drivers, but the 4040 wasn't one of them.

--
Bill Sloman, Nijmegen

On Fri, 26 Aug 2011 08:51:43 +1000, "Phil Allison" <phil_a@tpg.com.au>
wrote:

>
>"John Fields"
>>>
>>>"John Fields
>>> "Phil Allison"
>>>>
>>>>>"dave wanker"
>>>>>
>>>>>
>>>>>** FFS  -  define " low frequency "'
>>>>
>>>> Clue:
>>>>
>>>> "Best I've found so far might be the old 8038 function generator
>>>> chip."
>>>>
>>>
>>>**  WTF is your problem  -   shit head ???
>>>
>>>The 8083 operates from  0.001 Hz  to  300kHz.
>>>
>>>Which bit of that   FUCKING  ENORMOUS  range is automatically
>>>
>>> " low frequency "  ??????????    eh  ???
>>>
>>>You context blind,  ASD fucked, septic bloody moron.
>>
>> ---
>> Geez, Phil, when you pissue epithets like that it makes it difficult
>> for other than civilized players to reply to your feigned vitriol if
>> they have no emollient at hand.
>>
>> Is that what you want?
>
>
>**  Fuck off.
>
>> I have great respect for you and your point is taken.
>>
>> Mine was that, since the 8038 the OP considered as a baseline
>> candidate for his needs goes from wherever to wherever, another chip
>> sporting the same, or greater f(v) would work; the challenge being to
>> find that chip.
>
>
>** You posted nothing of the kind.
>
>    Piss off.
>
>
>....  Phil

R = R - 1

-- 
JF

On Aug 25, 2:43=A0pm, whit3rd <whit...@gmail.com> wrote:
> 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 do=
n't
> > > think that I've ever seen it used in any kind of programmable frequen=
cy
> > > generator.
> > =A0"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. =A0That's =A0how
> a Wein bridge works. =A0 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. =A0The 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. =A0

I'm waiting for someone to suggest using two ceramic Z5U caps as the
frequency tuning elements in a Wien bridge.
I'm not they would do the 50:1 frequency range.  Of course you'd have
to keep the AC amplitude relatively low.

George H.