Forums

oscillator with constant amplitude

Started by Tom Del Rosso August 5, 2015
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?

-- 


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?
I would use AGC. If wasting power is an issue then you're going about it more or less backwards -- at best, a linear oscillator on an unregulated rail with a constant output is going to use just as much power as an oscillator being powered through a linear regulator -- and it'll probably be worse. If you can run at a constant amplitude, use a switching regulator. What frequency range are you looking at? -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
On Wednesday, August 5, 2015 at 12:39:19 PM UTC-4, 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? > > --
Audio frequencies? I've done Wein bridges with amplitude control from diodes and resistor ratio's.. not great temperature coef. George H.
On Wed, 5 Aug 2015 12:39:09 -0400, "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> 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?
Here's a simple-minded one... <http://www.analog-innovations.com/SED/GyratorFilter_A1A_Oscillator.pdf> ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | 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.
On Wed, 5 Aug 2015 12:39:09 -0400, "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> 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?
A square wave could be made extremely stable; generate it from CMOS logic powered by a voltage regulator. The supply current would be almost entirely the load current, so the regulator really doesn't waste power.
"Jim Thompson" <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote in 
message news:hbh4satpp249v8ie3612nn6h2uv26ss0of@4ax.com...
> On Wed, 5 Aug 2015 12:39:09 -0400, "Tom Del Rosso" > <fizzbintuesday@that-google-mail-domain.com> 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? > > Here's a simple-minded one... > > <http://www.analog-innovations.com/SED/GyratorFilter_A1A_Oscillator.pdf> > > ...Jim Thompson > -- > | James E.Thompson | mens | > | Analog Innovations | et | > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > | San Tan Valley, AZ 85142 Skype: skypeanalog | | > | 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.
What do D5 and D6 do? Are they supposed to be back to back? I can see if they were zeners but 4148s?
On Wednesday, August 5, 2015 at 9:39:19 AM UTC-7, 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 ... with no power wasted
Easiest is a '555. If you regulate the reference resistor string, the 'triangle' waveform has regulated amplitude. Second-easiest is any oscillator with an AGC component. Consider phase-shift oscillators based on LM13700. See <http://www.ti.com/lit/ds/symlink/lm13700.pdf> Figure 38 oscillator takes two chips ( four amplifiers), but note that A1 has its current-program resistor (30k) free; you can gain-control there.
On Wed, 5 Aug 2015 13:46:42 -0400, "Tom Miller"
<tmiller11147@verizon.net> wrote:

> >"Jim Thompson" <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote in >message news:hbh4satpp249v8ie3612nn6h2uv26ss0of@4ax.com... >> On Wed, 5 Aug 2015 12:39:09 -0400, "Tom Del Rosso" >> <fizzbintuesday@that-google-mail-domain.com> 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? >> >> Here's a simple-minded one... >> >> <http://www.analog-innovations.com/SED/GyratorFilter_A1A_Oscillator.pdf> >> >> ...Jim Thompson >> -- >> | James E.Thompson | mens | >> | Analog Innovations | et | >> | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | >> | San Tan Valley, AZ 85142 Skype: skypeanalog | | >> | 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. > >What do D5 and D6 do? Are they supposed to be back to back? I can see if >they were zeners but 4148s? > > >
Miniscule amount of capacitance... in other words... a hack quickly thrown together. In practice I'd probably use a diff-pair with controlled tail current derived from measuring the amplitude... something simple like... <http://www.analog-innovations.com/SED/VCOwithAGC.pdf> >:-} ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Age gets better with wine!
On Wed, 5 Aug 2015, Jim Thompson wrote:

> On Wed, 5 Aug 2015 12:39:09 -0400, "Tom Del Rosso" > <fizzbintuesday@that-google-mail-domain.com> 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? > > Here's a simple-minded one... > > <http://www.analog-innovations.com/SED/GyratorFilter_A1A_Oscillator.pdf> >
What about the 1648 ECL VCO, that had built in AGC? Michael
On Thursday, 6 August 2015 02:39:19 UTC+10, 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?
The Wien bridge is the classic example - the necessary amplitude control scheme usually sets an amplitude that's independent of control voltage. LC oscillators use less current, and there's nothing to stop you using Wien-bridge style amplitude regulation to get a constant amplitude output independent of control voltage. I've got a current mirror variant of the Baxandall class-D oscillator which is less efficient than the classic Baxandall - which typically hits 90% efficiency or a bit better - but gets around 50% efficiency in the configurations I've looked at. The distortion performance isn't as good as a good Wien bridge - hysteresis in even a heavily gapped inductor means that it's hard to get the harmonic content better than about 100dB below the fundamental, but it's pretty good for a low-power oscillator, and way better than you'd get with a Wien bridge. -- Bill Sloman, Sydney