Forums

oscillator with constant amplitude

Started by Tom Del Rosso August 5, 2015
On Thu, 06 Aug 2015 15:28:56 -0400, Tom Del Rosso wrote:

> Tim Wescott wrote: >> On Wed, 05 Aug 2015 12:39:09 -0400, Tom Del Rosso wrote: >> >>> I don't want anybody to design it for me, but in general how would you >>> make an oscillator with a sine output of constant amplitude over a >>> range of supply voltage (let's say the operating range of the op-amp). >>> What I have in mind is a battery supply, but with no power wasted in >>> a regulator. Sure the oscillator would also waste power but not as >>> much. Would a square output be simpler? >> >> Can you get by with a squarer wave? If yes, then your easiest and most >> fuel-efficient way to do this would be to regulate with a switcher and >> then generate a square wave by any of the many acceptable ways. >> >> Just plain easiest, and not too bad on current consumption if you don't >> need any appreciable power on the output, would be a linear regulator >> powering your oscillator. >> >> Maybe tell us what this is for so we can ground our opinions in fact >> instead of spinning off into our own versions of theory-land? > > It's mainly for general knowledge, since my test signal doesn't have to > be that constant. I just got the idea that it must be possible, so, if > it was easy then I'd do it, or else just use a regulator. The Wein > Bridge is easy enough to be worth a try so I'll breadboard a few and try > it with a variable supply to see what happens. > > Thanks very much to all.
If you can find a suitable grain-o-wheat bulb it's fun to make a thermally stabilized oscillator. The bulbs aren't easy to find these days, though -- LEDs just don't work the same. -- www.wescottdesign.com
On Fri, 07 Aug 2015 06:07:39 +1000, Tim Wescott <tim@seemywebsite.com>  
wrote:

> On Thu, 06 Aug 2015 15:28:56 -0400, Tom Del Rosso wrote: > >> Tim Wescott wrote: >>> On Wed, 05 Aug 2015 12:39:09 -0400, Tom Del Rosso wrote: >>> >>>> I don't want anybody to design it for me, but in general how would you >>>> make an oscillator with a sine output of constant amplitude over a >>>> range of supply voltage (let's say the operating range of the op-amp). >>>> What I have in mind is a battery supply, but with no power wasted in >>>> a regulator. Sure the oscillator would also waste power but not as >>>> much. Would a square output be simpler? >>> >>> Can you get by with a squarer wave? If yes, then your easiest and most >>> fuel-efficient way to do this would be to regulate with a switcher and >>> then generate a square wave by any of the many acceptable ways. >>> >>> Just plain easiest, and not too bad on current consumption if you don't >>> need any appreciable power on the output, would be a linear regulator >>> powering your oscillator. >>> >>> Maybe tell us what this is for so we can ground our opinions in fact >>> instead of spinning off into our own versions of theory-land? >> >> It's mainly for general knowledge, since my test signal doesn't have to >> be that constant. I just got the idea that it must be possible, so, if >> it was easy then I'd do it, or else just use a regulator. The Wein >> Bridge is easy enough to be worth a try so I'll breadboard a few and try >> it with a variable supply to see what happens. >> >> Thanks very much to all. > > If you can find a suitable grain-o-wheat bulb it's fun to make a > thermally stabilized oscillator. > > The bulbs aren't easy to find these days, though -- LEDs just don't work > the same. >
J-fet
On Fri, 07 Aug 2015 06:31:16 +1000, David Eather wrote:

> On Fri, 07 Aug 2015 06:07:39 +1000, Tim Wescott <tim@seemywebsite.com> > wrote: > >> On Thu, 06 Aug 2015 15:28:56 -0400, Tom Del Rosso wrote: >> >>> Tim Wescott wrote: >>>> On Wed, 05 Aug 2015 12:39:09 -0400, Tom Del Rosso wrote: >>>> >>>>> I don't want anybody to design it for me, but in general how would >>>>> you make an oscillator with a sine output of constant amplitude over >>>>> a range of supply voltage (let's say the operating range of the >>>>> op-amp). >>>>> What I have in mind is a battery supply, but with no power wasted >>>>> in >>>>> a regulator. Sure the oscillator would also waste power but not as >>>>> much. Would a square output be simpler? >>>> >>>> Can you get by with a squarer wave? If yes, then your easiest and >>>> most fuel-efficient way to do this would be to regulate with a >>>> switcher and then generate a square wave by any of the many >>>> acceptable ways. >>>> >>>> Just plain easiest, and not too bad on current consumption if you >>>> don't need any appreciable power on the output, would be a linear >>>> regulator powering your oscillator. >>>> >>>> Maybe tell us what this is for so we can ground our opinions in fact >>>> instead of spinning off into our own versions of theory-land? >>> >>> It's mainly for general knowledge, since my test signal doesn't have >>> to be that constant. I just got the idea that it must be possible, >>> so, if it was easy then I'd do it, or else just use a regulator. The >>> Wein Bridge is easy enough to be worth a try so I'll breadboard a few >>> and try it with a variable supply to see what happens. >>> >>> Thanks very much to all. >> >> If you can find a suitable grain-o-wheat bulb it's fun to make a >> thermally stabilized oscillator. >> >> The bulbs aren't easy to find these days, though -- LEDs just don't >> work the same. >> >> > J-fet
I've done that. Distortion becomes more of an issue. Apparently there are (or at least were) some studio-quality mixers that were implemented by shining variable amounts of light onto CdS cells for low-noise, low-distortion variable resistance controlled by a DC voltage. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
On 8/6/2015 4:51 PM, Tim Wescott wrote:
> On Fri, 07 Aug 2015 06:31:16 +1000, David Eather wrote: > >> On Fri, 07 Aug 2015 06:07:39 +1000, Tim Wescott <tim@seemywebsite.com> >> wrote: >> >>> On Thu, 06 Aug 2015 15:28:56 -0400, Tom Del Rosso wrote: >>> >>>> Tim Wescott wrote: >>>>> On Wed, 05 Aug 2015 12:39:09 -0400, Tom Del Rosso wrote: >>>>> >>>>>> I don't want anybody to design it for me, but in general how would >>>>>> you make an oscillator with a sine output of constant amplitude over >>>>>> a range of supply voltage (let's say the operating range of the >>>>>> op-amp). >>>>>> What I have in mind is a battery supply, but with no power wasted >>>>>> in >>>>>> a regulator. Sure the oscillator would also waste power but not as >>>>>> much. Would a square output be simpler? >>>>> >>>>> Can you get by with a squarer wave? If yes, then your easiest and >>>>> most fuel-efficient way to do this would be to regulate with a >>>>> switcher and then generate a square wave by any of the many >>>>> acceptable ways. >>>>> >>>>> Just plain easiest, and not too bad on current consumption if you >>>>> don't need any appreciable power on the output, would be a linear >>>>> regulator powering your oscillator. >>>>> >>>>> Maybe tell us what this is for so we can ground our opinions in fact >>>>> instead of spinning off into our own versions of theory-land? >>>> >>>> It's mainly for general knowledge, since my test signal doesn't have >>>> to be that constant. I just got the idea that it must be possible, >>>> so, if it was easy then I'd do it, or else just use a regulator. The >>>> Wein Bridge is easy enough to be worth a try so I'll breadboard a few >>>> and try it with a variable supply to see what happens. >>>> >>>> Thanks very much to all. >>> >>> If you can find a suitable grain-o-wheat bulb it's fun to make a >>> thermally stabilized oscillator. >>> >>> The bulbs aren't easy to find these days, though -- LEDs just don't >>> work the same. >>> >>> >> J-fet > > I've done that. Distortion becomes more of an issue. > > Apparently there are (or at least were) some studio-quality mixers that > were implemented by shining variable amounts of light onto CdS cells for > low-noise, low-distortion variable resistance controlled by a DC voltage. >
Sure thing. I built circuits vaguely like that as a kid (audio companders for tape). Jim Williams went on a long digression about HP200A oscillators and JFETs and such, and came up with something pretty good, if a bit involved. http://tinyurl.com/nvyoqnh Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On Fri, 07 Aug 2015 06:51:32 +1000, Tim Wescott  
<seemywebsite@myfooter.really> wrote:

> On Fri, 07 Aug 2015 06:31:16 +1000, David Eather wrote: > >> On Fri, 07 Aug 2015 06:07:39 +1000, Tim Wescott <tim@seemywebsite.com> >> wrote: >> >>> On Thu, 06 Aug 2015 15:28:56 -0400, Tom Del Rosso wrote: >>> >>>> Tim Wescott wrote: >>>>> On Wed, 05 Aug 2015 12:39:09 -0400, Tom Del Rosso wrote: >>>>> >>>>>> I don't want anybody to design it for me, but in general how would >>>>>> you make an oscillator with a sine output of constant amplitude over >>>>>> a range of supply voltage (let's say the operating range of the >>>>>> op-amp). >>>>>> What I have in mind is a battery supply, but with no power wasted >>>>>> in >>>>>> a regulator. Sure the oscillator would also waste power but not as >>>>>> much. Would a square output be simpler? >>>>> >>>>> Can you get by with a squarer wave? If yes, then your easiest and >>>>> most fuel-efficient way to do this would be to regulate with a >>>>> switcher and then generate a square wave by any of the many >>>>> acceptable ways. >>>>> >>>>> Just plain easiest, and not too bad on current consumption if you >>>>> don't need any appreciable power on the output, would be a linear >>>>> regulator powering your oscillator. >>>>> >>>>> Maybe tell us what this is for so we can ground our opinions in fact >>>>> instead of spinning off into our own versions of theory-land? >>>> >>>> It's mainly for general knowledge, since my test signal doesn't have >>>> to be that constant. I just got the idea that it must be possible, >>>> so, if it was easy then I'd do it, or else just use a regulator. The >>>> Wein Bridge is easy enough to be worth a try so I'll breadboard a few >>>> and try it with a variable supply to see what happens. >>>> >>>> Thanks very much to all. >>> >>> If you can find a suitable grain-o-wheat bulb it's fun to make a >>> thermally stabilized oscillator. >>> >>> The bulbs aren't easy to find these days, though -- LEDs just don't >>> work the same. >>> >>> >> J-fet > > I've done that. Distortion becomes more of an issue. > > Apparently there are (or at least were) some studio-quality mixers that > were implemented by shining variable amounts of light onto CdS cells for > low-noise, low-distortion variable resistance controlled by a DC voltage. >
http://cds.linear.com/docs/en/application-note/an43f.pdf Has many ways to do it, including CDS cells or jfet (.002%) http://www.ti.com/lit/an/snoa665c/snoa665c.pdf uses a cap to block DC across the jfet for an improvement in THD they only claim .01% though. With a jfet with interchangeable D-S it does better
On Fri, 07 Aug 2015 07:29:32 +1000, David Eather <eather@tpg.com.au> wrote:

> On Fri, 07 Aug 2015 06:51:32 +1000, Tim Wescott > <seemywebsite@myfooter.really> wrote: > >> On Fri, 07 Aug 2015 06:31:16 +1000, David Eather wrote: >> >>> On Fri, 07 Aug 2015 06:07:39 +1000, Tim Wescott <tim@seemywebsite.com> >>> wrote: >>> >>>> On Thu, 06 Aug 2015 15:28:56 -0400, Tom Del Rosso wrote: >>>> >>>>> Tim Wescott wrote: >>>>>> On Wed, 05 Aug 2015 12:39:09 -0400, Tom Del Rosso wrote: >>>>>> >>>>>>> I don't want anybody to design it for me, but in general how would >>>>>>> you make an oscillator with a sine output of constant amplitude >>>>>>> over >>>>>>> a range of supply voltage (let's say the operating range of the >>>>>>> op-amp). >>>>>>> What I have in mind is a battery supply, but with no power wasted >>>>>>> in >>>>>>> a regulator. Sure the oscillator would also waste power but not as >>>>>>> much. Would a square output be simpler? >>>>>> >>>>>> Can you get by with a squarer wave? If yes, then your easiest and >>>>>> most fuel-efficient way to do this would be to regulate with a >>>>>> switcher and then generate a square wave by any of the many >>>>>> acceptable ways. >>>>>> >>>>>> Just plain easiest, and not too bad on current consumption if you >>>>>> don't need any appreciable power on the output, would be a linear >>>>>> regulator powering your oscillator. >>>>>> >>>>>> Maybe tell us what this is for so we can ground our opinions in fact >>>>>> instead of spinning off into our own versions of theory-land? >>>>> >>>>> It's mainly for general knowledge, since my test signal doesn't have >>>>> to be that constant. I just got the idea that it must be possible, >>>>> so, if it was easy then I'd do it, or else just use a regulator. The >>>>> Wein Bridge is easy enough to be worth a try so I'll breadboard a few >>>>> and try it with a variable supply to see what happens. >>>>> >>>>> Thanks very much to all. >>>> >>>> If you can find a suitable grain-o-wheat bulb it's fun to make a >>>> thermally stabilized oscillator. >>>> >>>> The bulbs aren't easy to find these days, though -- LEDs just don't >>>> work the same. >>>> >>>> >>> J-fet >> >> I've done that. Distortion becomes more of an issue. >> >> Apparently there are (or at least were) some studio-quality mixers that >> were implemented by shining variable amounts of light onto CdS cells for >> low-noise, low-distortion variable resistance controlled by a DC >> voltage. >> > > http://cds.linear.com/docs/en/application-note/an43f.pdf > > Has many ways to do it, including CDS cells or jfet (.002%) > > http://www.ti.com/lit/an/snoa665c/snoa665c.pdf > > uses a cap to block DC across the jfet for an improvement in THD they > only claim .01% though. With a jfet with interchangeable D-S it does > better
forgot - page 6
On Friday, 7 August 2015 07:29:11 UTC+10, David Eather  wrote:
> On Fri, 07 Aug 2015 06:51:32 +1000, Tim Wescott > <seemywebsite@myfooter.really> wrote: > > > On Fri, 07 Aug 2015 06:31:16 +1000, David Eather wrote: > > > >> On Fri, 07 Aug 2015 06:07:39 +1000, Tim Wescott <tim@seemywebsite.com> > >> wrote: > >> > >>> On Thu, 06 Aug 2015 15:28:56 -0400, Tom Del Rosso wrote: > >>> > >>>> Tim Wescott wrote: > >>>>> On Wed, 05 Aug 2015 12:39:09 -0400, Tom Del Rosso wrote: > >>>>> > >>>>>> I don't want anybody to design it for me, but in general how would > >>>>>> you make an oscillator with a sine output of constant amplitude over > >>>>>> a range of supply voltage (let's say the operating range of the > >>>>>> op-amp). > >>>>>> What I have in mind is a battery supply, but with no power wasted > >>>>>> in > >>>>>> a regulator. Sure the oscillator would also waste power but not as > >>>>>> much. Would a square output be simpler? > >>>>> > >>>>> Can you get by with a squarer wave? If yes, then your easiest and > >>>>> most fuel-efficient way to do this would be to regulate with a > >>>>> switcher and then generate a square wave by any of the many > >>>>> acceptable ways. > >>>>> > >>>>> Just plain easiest, and not too bad on current consumption if you > >>>>> don't need any appreciable power on the output, would be a linear > >>>>> regulator powering your oscillator. > >>>>> > >>>>> Maybe tell us what this is for so we can ground our opinions in fact > >>>>> instead of spinning off into our own versions of theory-land? > >>>> > >>>> It's mainly for general knowledge, since my test signal doesn't have > >>>> to be that constant. I just got the idea that it must be possible, > >>>> so, if it was easy then I'd do it, or else just use a regulator. The > >>>> Wein Bridge is easy enough to be worth a try so I'll breadboard a few > >>>> and try it with a variable supply to see what happens. > >>>> > >>>> Thanks very much to all. > >>> > >>> If you can find a suitable grain-o-wheat bulb it's fun to make a > >>> thermally stabilized oscillator. > >>> > >>> The bulbs aren't easy to find these days, though -- LEDs just don't > >>> work the same. > >>> > >>> > >> J-fet > > > > I've done that. Distortion becomes more of an issue. > > > > Apparently there are (or at least were) some studio-quality mixers that > > were implemented by shining variable amounts of light onto CdS cells for > > low-noise, low-distortion variable resistance controlled by a DC voltage. > > > > http://cds.linear.com/docs/en/application-note/an43f.pdf > > Has many ways to do it, including CDS cells or jfet (.002%) > > http://www.ti.com/lit/an/snoa665c/snoa665c.pdf > > uses a cap to block DC across the jfet for an improvement in THD they only > claim .01% though. With a jfet with interchangeable D-S it does better.
Few jfets don't have interchangeable drain and source connections. Winfield Hill's AOE 3 gives and example as figure 7.22 on page 438. He uses the drain-gate divider trick on the jfet to minimise distortion (which Jim Williams missed in AN-43 at Fig.43). The National Semiconductor LME49710 might have been a better choice of op amp. -- Bill Sloman, Sydney
On Friday, 7 August 2015 05:29:02 UTC+10, Tom Del Rosso  wrote:
> Tim Wescott wrote: > > On Wed, 05 Aug 2015 12:39:09 -0400, Tom Del Rosso wrote: > > > >> I don't want anybody to design it for me, but in general how would > >> you make an oscillator with a sine output of constant amplitude over > >> a range of supply voltage (let's say the operating range of the > >> op-amp). What I have in mind is a battery supply, but with no power > >> wasted in a regulator. Sure the oscillator would also waste power > >> but not as much. Would a square output be simpler? > > > > Can you get by with a squarer wave? If yes, then your easiest and > > most fuel-efficient way to do this would be to regulate with a > > switcher and then generate a square wave by any of the many > > acceptable ways. > > > > Just plain easiest, and not too bad on current consumption if you > > don't need any appreciable power on the output, would be a linear > > regulator powering your oscillator. > > > > Maybe tell us what this is for so we can ground our opinions in fact > > instead of spinning off into our own versions of theory-land? > > It's mainly for general knowledge, since my test signal doesn't have to > be that constant. I just got the idea that it must be possible, so, if > it was easy then I'd do it, or else just use a regulator. The Wein > Bridge is easy enough to be worth a try so I'll breadboard a few and try > it with a variable supply to see what happens.
Probably not the best approach if you want to minimise current consumption. E-mail me - at bill.sloman@ieee.org - for an alternative. Tell me your preferred frequency and I might be able to tailor my solution. -- Bill Sloman, Sydney
On Fri, 07 Aug 2015 12:50:46 +1000, Bill Sloman <bill.sloman@gmail.com>  
wrote:

> On Friday, 7 August 2015 07:29:11 UTC+10, David Eather wrote: >> On Fri, 07 Aug 2015 06:51:32 +1000, Tim Wescott >> <seemywebsite@myfooter.really> wrote: >> >> > On Fri, 07 Aug 2015 06:31:16 +1000, David Eather wrote: >> > >> >> On Fri, 07 Aug 2015 06:07:39 +1000, Tim Wescott >> <tim@seemywebsite.com> >> >> wrote: >> >> >> >>> On Thu, 06 Aug 2015 15:28:56 -0400, Tom Del Rosso wrote: >> >>> >> >>>> Tim Wescott wrote: >> >>>>> On Wed, 05 Aug 2015 12:39:09 -0400, Tom Del Rosso wrote: >> >>>>> >> >>>>>> I don't want anybody to design it for me, but in general how >> would >> >>>>>> you make an oscillator with a sine output of constant amplitude >> over >> >>>>>> a range of supply voltage (let's say the operating range of the >> >>>>>> op-amp). >> >>>>>> What I have in mind is a battery supply, but with no power >> wasted >> >>>>>> in >> >>>>>> a regulator. Sure the oscillator would also waste power but not >> as >> >>>>>> much. Would a square output be simpler? >> >>>>> >> >>>>> Can you get by with a squarer wave? If yes, then your easiest and >> >>>>> most fuel-efficient way to do this would be to regulate with a >> >>>>> switcher and then generate a square wave by any of the many >> >>>>> acceptable ways. >> >>>>> >> >>>>> Just plain easiest, and not too bad on current consumption if you >> >>>>> don't need any appreciable power on the output, would be a linear >> >>>>> regulator powering your oscillator. >> >>>>> >> >>>>> Maybe tell us what this is for so we can ground our opinions in >> fact >> >>>>> instead of spinning off into our own versions of theory-land? >> >>>> >> >>>> It's mainly for general knowledge, since my test signal doesn't >> have >> >>>> to be that constant. I just got the idea that it must be possible, >> >>>> so, if it was easy then I'd do it, or else just use a regulator. >> The >> >>>> Wein Bridge is easy enough to be worth a try so I'll breadboard a >> few >> >>>> and try it with a variable supply to see what happens. >> >>>> >> >>>> Thanks very much to all. >> >>> >> >>> If you can find a suitable grain-o-wheat bulb it's fun to make a >> >>> thermally stabilized oscillator. >> >>> >> >>> The bulbs aren't easy to find these days, though -- LEDs just don't >> >>> work the same. >> >>> >> >>> >> >> J-fet >> > >> > I've done that. Distortion becomes more of an issue. >> > >> > Apparently there are (or at least were) some studio-quality mixers >> that >> > were implemented by shining variable amounts of light onto CdS cells >> for >> > low-noise, low-distortion variable resistance controlled by a DC >> voltage. >> > >> >> http://cds.linear.com/docs/en/application-note/an43f.pdf >> >> Has many ways to do it, including CDS cells or jfet (.002%) >> >> http://www.ti.com/lit/an/snoa665c/snoa665c.pdf >> >> uses a cap to block DC across the jfet for an improvement in THD they >> only >> claim .01% though. With a jfet with interchangeable D-S it does better. > > Few jfets don't have interchangeable drain and source connections.
perhaps the word symmetrical would have been better
> > Winfield Hill's AOE 3 gives and example as figure 7.22 on page 438. He > uses the drain-gate divider trick on the jfet to minimise distortion > (which Jim Williams missed in AN-43 at Fig.43).
but is in the ap note no the less.
> > The National Semiconductor LME49710 might have been a better choice of > op amp.
On Thursday, August 6, 2015 at 3:29:02 PM UTC-4, Tom Del Rosso wrote:
> Tim Wescott wrote: > > On Wed, 05 Aug 2015 12:39:09 -0400, Tom Del Rosso wrote: > > > >> I don't want anybody to design it for me, but in general how would > >> you make an oscillator with a sine output of constant amplitude over > >> a range of supply voltage (let's say the operating range of the > >> op-amp). What I have in mind is a battery supply, but with no power > >> wasted in a regulator. Sure the oscillator would also waste power > >> but not as much. Would a square output be simpler? > > > > Can you get by with a squarer wave? If yes, then your easiest and > > most fuel-efficient way to do this would be to regulate with a > > switcher and then generate a square wave by any of the many > > acceptable ways. > > > > Just plain easiest, and not too bad on current consumption if you > > don't need any appreciable power on the output, would be a linear > > regulator powering your oscillator. > > > > Maybe tell us what this is for so we can ground our opinions in fact > > instead of spinning off into our own versions of theory-land? > > It's mainly for general knowledge, since my test signal doesn't have to > be that constant. I just got the idea that it must be possible, so, if > it was easy then I'd do it, or else just use a regulator. The Wein > Bridge is easy enough to be worth a try so I'll breadboard a few and try > it with a variable supply to see what happens. > > Thanks very much to all. > > --
If you don't care too much about distortion the Wein bridge w/ diode limiting can keep the 3rd harmonic down to the 0.1 to 1% level. You can make it a bit better by taking the output (with another opamp as buffer) from the non-inverting input. (You get a little RC filtering "for free".) (DDS has taken a lot of the fun out of oscillator circuits.) George H.