# 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 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
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"
>
>>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 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 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/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>
>
What about the 1648 ECL VCO, that had built in AGC?

Michael
```
```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?

ICL8038 or similar triangle wave generator with built in triangle to
sine converter ?

```
```More responses than I expected.  I appreciate it but can't respond to
all right now.

Tim Wescott wrote:
>
> 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.

I understand what you mean.  The idea came that it must be possible, but
I've never seen it done specifically, so I got curious about how complex
such an oscillator would be.  More complex than a regulator it turns
out.

> If you can run at a constant amplitude, use a switching regulator.
>
> What frequency range are you looking at?

Low KHz.

--

```
```On 06/08/15 17:03, Tom Del Rosso wrote:
> More responses than I expected.  I appreciate it but can't respond to
> all right now.
> Tim Wescott wrote:
>> 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.
> I understand what you mean.  The idea came that it must be possible, but
> I've never seen it done specifically, so I got curious about how complex
> such an oscillator would be.  More complex than a regulator it turns
> out.

Here's an example of an oscillator (for 3.6MHz) that uses AGC.
It's not very complicated, though it's unsuitable for "Low KHz"
because of the size of the inductor you need.

If you want to run it, you'll need to supply a transistor model,
as I didn't include my library part (and you might need to change
some resistor values for the AGC to work). But I suspect you'll be
able to see how it works without doing that (use LTSpice to view!)

Clifford Heath.

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```