# oscillator with constant amplitude

Started by 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"

>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/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"

>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
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"
>
>>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/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.

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"
>>
>>>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/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/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"
>
>> 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>
>

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

```