On Tue, 27 Sep 2011 09:54:36 -0700, George Herold wrote:
> 30kHz to 100kHz VCO with sine wave output.
>
> I know this has been covered before in previous threads.
>
> The obvious way to do this is a digital signal generator (DSG) IC with
> maybe an A-D to measure the voltage. I've not done much digital stuff
> in a while, so this has a bit of a learning curve. But if anyone has
> some good chips to look at or app notes then please do share. I've been
> looking at IC's on Analogs web site, but there are a lot to choose from!
>
> I was also thinking I could do this with a ~20MHz varactor controlled
> VCO as a variable clock into a DSG chip. This looks easier to my
> unsophisticated digital mind.
>
> Finally I offer the following, a Wien bridge oscillator with varactor
> diodes as the capacitors. I was also thinking I could use crappy Z5U
> ceramic caps instead of the varactors.
>
> http://imageshack.us/photo/my-images/88/wien1.jpg/
>
> (Excuse my chicken scratching.)
> Comments welcome.
Back in the 70's we used reverse biased LEDs instead of varactor
diodes. They had substantial capacitance and worked reasonably
well. However this was one-off stuff in the research labs and not
anything designed for production.
Art
Reply by Tim Wescott●November 7, 20112011-11-07
On Tue, 27 Sep 2011 09:54:36 -0700, George Herold wrote:
> 30kHz to 100kHz VCO with sine wave output.
>
> I know this has been covered before in previous threads.
>
> The obvious way to do this is a digital signal generator (DSG) IC with
> maybe an A-D to measure the voltage. I’ve not done much digital stuff
> in a while, so this has a bit of a learning curve. But if anyone has
> some good chips to look at or app notes then please do share. I've been
> looking at IC's on Analogs web site, but there are a lot to choose from!
>
> I was also thinking I could do this with a ~20MHz varactor controlled
> VCO as a variable clock into a DSG chip. This looks easier to my
> unsophisticated digital mind.
>
> Finally I offer the following, a Wien bridge oscillator with varactor
> diodes as the capacitors. I was also thinking I could use crappy Z5U
> ceramic caps instead of the varactors.
>
> http://imageshack.us/photo/my-images/88/wien1.jpg/
>
> (Excuse my chicken scratching.)
> Comments welcome.
Last I heard you were doing well with your 300-1000kHz oscillator and
4017 sine generator.
But just for chuckles I thought I'd mention this: I just had occasion to
breadboard a tunable low-pass filter for a project (it's pretending to be
a $5000 device that, for some reason, my customer doesn't want to buy a
second version of just to ship to me).
I ended up building a Sallen-Key filter, using resistors that were
switched in and out of circuit with a 4066 at 1MHz and a variable duty
cycle. The overall effect of the thing (aside from some 1MHz scrud
'cause it's built on a godforsaken proto board) is to smoothly tune from
10kHz to 20kHz under control of a voltage from a DAC.
It occurs to me that you could do this with a Wien bridge oscillator: the
effective average resistance is R/rho, where rho is the duty cycle of the
switch. This means that you can vary your frequency from some maximum
down to zero, simply by varying the switch duty cycle. Moreover, you can
use one of the unused switches in the package for AGC.
Not that you should change anything: I'm just having fun dinking with
prototype circuits that never have to work outside the lab, and I thought
I'd share...
--
www.wescottdesign.com
Reply by John Larkin●October 7, 20112011-10-07
On Fri, 7 Oct 2011 05:34:25 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:
>On Oct 6, 7:12�pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
>Web-Site.com> wrote:
>> On Tue, 27 Sep 2011 09:54:36 -0700 (PDT), George Herold
>>
>>
>>
>>
>>
>> <gher...@teachspin.com> wrote:
>> >30kHz to 100kHz VCO with sine wave output.
>>
>> >I know this has been covered before in previous threads.
>>
>> >The obvious way to do this is a digital signal generator (DSG) IC with
>> >maybe an A-D to measure the voltage. �I ve not done much digital stuff
>> >in a while, so this has a bit of a learning curve. �But if anyone has
>> >some good chips to look at or app notes then please do share. �I've
>> >been looking at IC's on Analogs web site, but there are a lot to
>> >choose from!
>>
>> >I was also thinking I could do this with a ~20MHz varactor controlled
>> >VCO as a variable clock into a DSG chip. �This looks easier to my
>> >unsophisticated digital mind.
>>
>> >Finally I offer the following, �a Wien bridge oscillator �with
>> >varactor diodes as the capacitors. � �I was also thinking I could use
>> >crappy Z5U ceramic caps instead of the varactors.
>>
>> >http://imageshack.us/photo/my-images/88/wien1.jpg/
>>
>> >(Excuse my chicken scratching.)
>> >Comments welcome.
>>
>> >George H.
>>
>> 3.3:1 in frequency is ~11:1 in capacitance. �I'd go with one of the
>> cheapy A-to-D approaches, although a sawtooth integrated twice is nice
>> if you don't mind using some kind of leveling AGC.
>>
>> � � � � � � � � � � � � � � � � � � � � ...Jim Thompson
>> --
>> | James E.Thompson, CTO � � � � � � � � � � � � � �| � �mens � � |
>> | Analog Innovations, Inc. � � � � � � � � � � � � | � � et � � �|
>> | Analog/Mixed-Signal ASIC's and Discrete Systems �| � �manus � �|
>> | Phoenix, Arizona �85048 � �Skype: Contacts Only �| � � � � � � |
>> | Voice:(480)460-2350 �Fax: Available upon request | �Brass Rat �|
>> | E-mail Icon athttp://www.analog-innovations.com| � �1962 � � |
>>
>> I love to cook with wine. � � Sometimes I even put it in the food.- Hide quoted text -
>>
>> - Show quoted text -
>
>Thanks Jim, I've pretty much abandoned the above Wien-bridge thing.
>I'm pretty sure I could make it work... but I'd be disappointed with
>the distortion...I'd guess something like 1%.
>
>I did order some of the 4017 decade counters. (Phil H's suggestion.)
>That design has a little digital in it.
>I'm picturing Monty Python...paraphrasing, "The Spam, eggs, bacon and
>Spam, only has a little Spam in it."
>
>George H.
One cute sinewave source is a VCO that clocks a switched-capacitor
filter at 100*f, and a 100:1 divider to make square wave "f". Use the
filter to make the square wave into a sine. Lots of interesting
variants and gotchas.
http://www.national.com/mpf/LM/LMF100.html#Overview
John
Reply by George Herold●October 7, 20112011-10-07
On Oct 6, 7:12=A0pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
Web-Site.com> wrote:
> On Tue, 27 Sep 2011 09:54:36 -0700 (PDT), George Herold
>
>
>
>
>
> <gher...@teachspin.com> wrote:
> >30kHz to 100kHz VCO with sine wave output.
>
> >I know this has been covered before in previous threads.
>
> >The obvious way to do this is a digital signal generator (DSG) IC with
> >maybe an A-D to measure the voltage. =A0I ve not done much digital stuff
> >in a while, so this has a bit of a learning curve. =A0But if anyone has
> >some good chips to look at or app notes then please do share. =A0I've
> >been looking at IC's on Analogs web site, but there are a lot to
> >choose from!
>
> >I was also thinking I could do this with a ~20MHz varactor controlled
> >VCO as a variable clock into a DSG chip. =A0This looks easier to my
> >unsophisticated digital mind.
>
> >Finally I offer the following, =A0a Wien bridge oscillator =A0with
> >varactor diodes as the capacitors. =A0 =A0I was also thinking I could us=
e
> >crappy Z5U ceramic caps instead of the varactors.
>
> >http://imageshack.us/photo/my-images/88/wien1.jpg/
>
> >(Excuse my chicken scratching.)
> >Comments welcome.
>
> >George H.
>
> 3.3:1 in frequency is ~11:1 in capacitance. =A0I'd go with one of the
> cheapy A-to-D approaches, although a sawtooth integrated twice is nice
> if you don't mind using some kind of leveling AGC.
>
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
> | Voice:(480)460-2350 =A0Fax: Available upon request | =A0Brass Rat =A0|
> | E-mail Icon athttp://www.analog-innovations.com| =A0 =A01962 =A0 =A0 |
>
> I love to cook with wine. =A0 =A0 Sometimes I even put it in the food.- H=
ide quoted text -
>
> - Show quoted text -
Thanks Jim, I've pretty much abandoned the above Wien-bridge thing.
I'm pretty sure I could make it work... but I'd be disappointed with
the distortion...I'd guess something like 1%.
I did order some of the 4017 decade counters. (Phil H's suggestion.)
That design has a little digital in it.
I'm picturing Monty Python...paraphrasing, "The Spam, eggs, bacon and
Spam, only has a little Spam in it."
George H.
Reply by Tim Wescott●October 6, 20112011-10-06
On Thu, 06 Oct 2011 16:12:13 -0700, Jim Thompson wrote:
> On Tue, 27 Sep 2011 09:54:36 -0700 (PDT), George Herold
> <gherold@teachspin.com> wrote:
>
>>30kHz to 100kHz VCO with sine wave output.
>>
>>I know this has been covered before in previous threads.
>>
>>The obvious way to do this is a digital signal generator (DSG) IC with
>>maybe an A-D to measure the voltage. I’ve not done much digital stuff
>>in a while, so this has a bit of a learning curve. But if anyone has
>>some good chips to look at or app notes then please do share. I've been
>>looking at IC's on Analogs web site, but there are a lot to choose from!
>>
>>I was also thinking I could do this with a ~20MHz varactor controlled
>>VCO as a variable clock into a DSG chip. This looks easier to my
>>unsophisticated digital mind.
>>
>>Finally I offer the following, a Wien bridge oscillator with varactor
>>diodes as the capacitors. I was also thinking I could use crappy Z5U
>>ceramic caps instead of the varactors.
>>
>>http://imageshack.us/photo/my-images/88/wien1.jpg/
>>
>>(Excuse my chicken scratching.)
>>Comments welcome.
>>
>>George H.
>
> 3.3:1 in frequency is ~11:1 in capacitance. I'd go with one of the
> cheapy A-to-D approaches, although a sawtooth integrated twice is nice
> if you don't mind using some kind of leveling AGC.
It's 3.3:1 in capacitance if you gang-tune a pair of capacitors in a Wien
bridge. That's still impractically large, but that's what it is.
It's 11:1 if you're tuning against a fixed inductor.
--
www.wescottdesign.com
Reply by Jim Thompson●October 6, 20112011-10-06
On Tue, 27 Sep 2011 09:54:36 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:
>30kHz to 100kHz VCO with sine wave output.
>
>I know this has been covered before in previous threads.
>
>The obvious way to do this is a digital signal generator (DSG) IC with
>maybe an A-D to measure the voltage. I�ve not done much digital stuff
>in a while, so this has a bit of a learning curve. But if anyone has
>some good chips to look at or app notes then please do share. I've
>been looking at IC's on Analogs web site, but there are a lot to
>choose from!
>
>I was also thinking I could do this with a ~20MHz varactor controlled
>VCO as a variable clock into a DSG chip. This looks easier to my
>unsophisticated digital mind.
>
>Finally I offer the following, a Wien bridge oscillator with
>varactor diodes as the capacitors. I was also thinking I could use
>crappy Z5U ceramic caps instead of the varactors.
>
>http://imageshack.us/photo/my-images/88/wien1.jpg/
>
>(Excuse my chicken scratching.)
>Comments welcome.
>
>George H.
3.3:1 in frequency is ~11:1 in capacitance. I'd go with one of the
cheapy A-to-D approaches, although a sawtooth integrated twice is nice
if you don't mind using some kind of leveling AGC.
...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Reply by Rich Webb●October 4, 20112011-10-04
On Tue, 04 Oct 2011 11:01:11 -0500, John S <sophi.2@invalid.org> wrote:
>On 10/4/2011 8:58 AM, Rich Webb wrote:
>> On Tue, 4 Oct 2011 06:47:21 -0700 (PDT), George Herold
>> <gherold@teachspin.com> wrote:
>>
>>> On Sep 30, 2:01 pm, me0...@yahoo.com wrote:
>>>> Good luck George,
>>>>
>>>> I won't beat a dead horse, but the DDS really sounds like it was
>>>> designed for your app.
>>>>
>>>> Have a look at there app notes if you already haven't. Depending on
>>>> the part, great freq resolution, modulation capability and crystal
>>>> stability.
>>>>
>>>> Regards- Hide quoted text -
>>>>
>>>> - Show quoted text -
>>>
>>> No problem MeO, A DDS design ....someday...
>>
>> You really don't need a purpose-built DDS chip to do direct digital
>> synthesis. This project constructed around a (relatively) ancient
>> AT90S2313 chip<http://www.myplace.nu/avr/minidds/index.htm> is a good
>> example. It can be expanded to fractional-N and more bells and whistles
>> (literally, I'd imagine ;-) but the basic principal is pretty
>> straightforward.
>>
>
>Nice! I think I'd like to try it using a Cypress PSoC to make a tiny DDS
>for the range of about .1 Hz to 10 kHz or so.
>
>Thanks.
Happy to have provided the pointer -- it's not my project but I did play
around with it, back in the day. Fun stuff!
--
Rich Webb Norfolk, VA
Reply by Michael A. Terrell●October 4, 20112011-10-04
John S wrote:
>
> On 10/4/2011 8:58 AM, Rich Webb wrote:
> > On Tue, 4 Oct 2011 06:47:21 -0700 (PDT), George Herold
> > <gherold@teachspin.com> wrote:
> >
> >> On Sep 30, 2:01 pm, me0...@yahoo.com wrote:
> >>> Good luck George,
> >>>
> >>> I won't beat a dead horse, but the DDS really sounds like it was
> >>> designed for your app.
> >>>
> >>> Have a look at there app notes if you already haven't. Depending on
> >>> the part, great freq resolution, modulation capability and crystal
> >>> stability.
> >>>
> >>> Regards- Hide quoted text -
> >>>
> >>> - Show quoted text -
> >>
> >> No problem MeO, A DDS design ....someday...
> >
> > You really don't need a purpose-built DDS chip to do direct digital
> > synthesis. This project constructed around a (relatively) ancient
> > AT90S2313 chip<http://www.myplace.nu/avr/minidds/index.htm> is a good
> > example. It can be expanded to fractional-N and more bells and whistles
> > (literally, I'd imagine ;-) but the basic principal is pretty
> > straightforward.
> >
>
> Nice! I think I'd like to try it using a Cypress PSoC to make a tiny DDS
> for the range of about .1 Hz to 10 kHz or so.
Tiny? look at the Analog Devices AD9833. It's a 10 pin SOIC.
--
You can't have a sense of humor, if you have no sense.
Reply by John S●October 4, 20112011-10-04
On 10/4/2011 8:58 AM, Rich Webb wrote:
> On Tue, 4 Oct 2011 06:47:21 -0700 (PDT), George Herold
> <gherold@teachspin.com> wrote:
>
>> On Sep 30, 2:01 pm, me0...@yahoo.com wrote:
>>> Good luck George,
>>>
>>> I won't beat a dead horse, but the DDS really sounds like it was
>>> designed for your app.
>>>
>>> Have a look at there app notes if you already haven't. Depending on
>>> the part, great freq resolution, modulation capability and crystal
>>> stability.
>>>
>>> Regards- Hide quoted text -
>>>
>>> - Show quoted text -
>>
>> No problem MeO, A DDS design ....someday...
>
> You really don't need a purpose-built DDS chip to do direct digital
> synthesis. This project constructed around a (relatively) ancient
> AT90S2313 chip<http://www.myplace.nu/avr/minidds/index.htm> is a good
> example. It can be expanded to fractional-N and more bells and whistles
> (literally, I'd imagine ;-) but the basic principal is pretty
> straightforward.
>
Nice! I think I'd like to try it using a Cypress PSoC to make a tiny DDS
for the range of about .1 Hz to 10 kHz or so.
Thanks.
John S
Reply by George Herold●October 4, 20112011-10-04
On Oct 1, 12:24=A0pm, "cbarn24...@aol.com" <cbarn24...@aol.com> wrote:
> =A0>
>
> > > If you=92ve never done this before I would discourage you:
>
> > > I=92m just trying to be helpful and I wish you the best of luck.
>
> > Thanks again. =A0At the moment I'm just going to order some VCO's from
> > minicirciuts... (throw some money at the problem.) and see what the
> > output looks like. =A0I'll also push forward on the triangle wave/ sine
> > shaper idea.
>
> Download the tek FG02 to see how to do it.http://bama.edebris.com/manuals=
/tek/fg502/
>
>
>
>
>
> > This is a nice app note,http://www.national.com/an/AN/AN-263.pdf
>
> > George H.
>
> > > Btw, you do want to go with frequencies up over 10MHz. =A0Get far awa=
y
> > > from your baseband, just makes the IF filtering all that much
> > > easier.- Hide quoted text -
>
> > > - Show quoted text -- Hide quoted text -
>
> > - Show quoted text -- Hide quoted text -
>
> > - Show quoted text -- Hide quoted text -
>
> - Show quoted text -
Thanks, I don't quite get the diode bridges. I was going to try
Phil's tanh shaper idea. (logarthimic shaper in the AN263 app note.)
George H.